A Quick Guide to Go's Assembler - The Go Programming Language (2022)

A Quick Guide to Go's Assembler

This document is a quick outline of the unusual form of assembly language used by the gc Go compiler.The document is not comprehensive.

The assembler is based on the input style of the Plan 9 assemblers, which is documented in detailelsewhere.If you plan to write assembly language, you should read that document although much of it is Plan 9-specific.The current document provides a summary of the syntax and the differences withwhat is explained in that document, anddescribes the peculiarities that apply when writing assembly code to interact with Go.

The most important thing to know about Go's assembler is that it is not a direct representation of the underlying machine.Some of the details map precisely to the machine, but some do not.This is because the compiler suite (seethis description)needs no assembler pass in the usual pipeline.Instead, the compiler operates on a kind of semi-abstract instruction set,and instruction selection occurs partly after code generation.The assembler works on the semi-abstract form, sowhen you see an instruction like MOVwhat the toolchain actually generates for that operation mightnot be a move instruction at all, perhaps a clear or load.Or it might correspond exactly to the machine instruction with that name.In general, machine-specific operations tend to appear as themselves, while more general concepts likememory move and subroutine call and return are more abstract.The details vary with architecture, and we apologize for the imprecision; the situation is not well-defined.

The assembler program is a way to parse a description of thatsemi-abstract instruction set and turn it into instructions to beinput to the linker.If you want to see what the instructions look like in assembly for a given architecture, say amd64, thereare many examples in the sources of the standard library, in packages such asruntime andmath/big.You can also examine what the compiler emits as assembly code(the actual output may differ from what you see here):

$ cat x.gopackage mainfunc main() {println(3)}$ GOOS=linux GOARCH=amd64 go tool compile -S x.go # or: go build -gcflags -S x.go"".main STEXT size=74 args=0x0 locals=0x100x0000 00000 (x.go:3)TEXT"".main(SB), $16-00x0000 00000 (x.go:3)MOVQ(TLS), CX0x0009 00009 (x.go:3)CMPQSP, 16(CX)0x000d 00013 (x.go:3)JLS670x000f 00015 (x.go:3)SUBQ$16, SP0x0013 00019 (x.go:3)MOVQBP, 8(SP)0x0018 00024 (x.go:3)LEAQ8(SP), BP0x001d 00029 (x.go:3)FUNCDATA$0, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)0x001d 00029 (x.go:3)FUNCDATA$1, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)0x001d 00029 (x.go:3)FUNCDATA$2, gclocals·33cdeccccebe80329f1fdbee7f5874cb(SB)0x001d 00029 (x.go:4)PCDATA$0, $00x001d 00029 (x.go:4)PCDATA$1, $00x001d 00029 (x.go:4)CALLruntime.printlock(SB)0x0022 00034 (x.go:4)MOVQ$3, (SP)0x002a 00042 (x.go:4)CALLruntime.printint(SB)0x002f 00047 (x.go:4)CALLruntime.printnl(SB)0x0034 00052 (x.go:4)CALLruntime.printunlock(SB)0x0039 00057 (x.go:5)MOVQ8(SP), BP0x003e 00062 (x.go:5)ADDQ$16, SP0x0042 00066 (x.go:5)RET0x0043 00067 (x.go:5)NOP0x0043 00067 (x.go:3)PCDATA$1, $-10x0043 00067 (x.go:3)PCDATA$0, $-10x0043 00067 (x.go:3)CALLruntime.morestack_noctxt(SB)0x0048 00072 (x.go:3)JMP0...

The FUNCDATA and PCDATA directives contain informationfor use by the garbage collector; they are introduced by the compiler.

To see what gets put in the binary after linking, use go tool objdump:

$ go build -o x.exe x.go$ go tool objdump -s main.main x.exeTEXT main.main(SB) /tmp/x.go x.go:30x10501c065488b0c2530000000MOVQ GS:0x30, CX x.go:30x10501c9483b6110CMPQ 0x10(CX), SP x.go:30x10501cd7634JBE 0x1050203 x.go:30x10501cf4883ec10SUBQ $0x10, SP x.go:30x10501d348896c2408MOVQ BP, 0x8(SP) x.go:30x10501d8488d6c2408LEAQ 0x8(SP), BP x.go:40x10501dde86e45fdffCALL runtime.printlock(SB) x.go:40x10501e248c7042403000000MOVQ $0x3, 0(SP) x.go:40x10501eae8e14cfdffCALL runtime.printint(SB) x.go:40x10501efe8ec47fdffCALL runtime.printnl(SB) x.go:40x10501f4e8d745fdffCALL runtime.printunlock(SB) x.go:50x10501f9488b6c2408MOVQ 0x8(SP), BP x.go:50x10501fe4883c410ADDQ $0x10, SP x.go:50x1050202c3RET x.go:30x1050203e83882ffffCALL runtime.morestack_noctxt(SB) x.go:30x1050208ebb6JMP main.main(SB)

Constants

Although the assembler takes its guidance from the Plan 9 assemblers,it is a distinct program, so there are some differences.One is in constant evaluation.Constant expressions in the assembler are parsed using Go's operatorprecedence, not the C-like precedence of the original.Thus 3&1<<2 is 4, not 0—it parses as (3&1)<<2not 3&(1<<2).Also, constants are always evaluated as 64-bit unsigned integers.Thus -2 is not the integer value minus two,but the unsigned 64-bit integer with the same bit pattern.The distinction rarely matters butto avoid ambiguity, division or right shift where the right operand'shigh bit is set is rejected.

Symbols

Some symbols, such as R1 or LR,are predefined and refer to registers.The exact set depends on the architecture.

There are four predeclared symbols that refer to pseudo-registers.These are not real registers, but rather virtual registers maintained bythe toolchain, such as a frame pointer.The set of pseudo-registers is the same for all architectures:

  • FP: Frame pointer: arguments and locals.
  • PC: Program counter:jumps and branches.
  • SB: Static base pointer: global symbols.
  • SP: Stack pointer: the highest address within the local stack frame.

All user-defined symbols are written as offsets to the pseudo-registersFP (arguments and locals) and SB (globals).

The SB pseudo-register can be thought of as the origin of memory, so the symbol foo(SB)is the name foo as an address in memory.This form is used to name global functions and data.Adding <> to the name, as in foo<>(SB), makes the namevisible only in the current source file, like a top-level static declaration in a C file.Adding an offset to the name refers to that offset from the symbol's address, sofoo+4(SB) is four bytes past the start of foo.

The FP pseudo-register is a virtual frame pointerused to refer to function arguments.The compilers maintain a virtual frame pointer and refer to the arguments on the stack as offsets from that pseudo-register.Thus 0(FP) is the first argument to the function,8(FP) is the second (on a 64-bit machine), and so on.However, when referring to a function argument this way, it is necessary to place a nameat the beginning, as in first_arg+0(FP) and second_arg+8(FP).(The meaning of the offset—offset from the frame pointer—distinctfrom its use with SB, where it is an offset from the symbol.)The assembler enforces this convention, rejecting plain 0(FP) and 8(FP).The actual name is semantically irrelevant but should be used to documentthe argument's name.It is worth stressing that FP is always apseudo-register, not a hardwareregister, even on architectures with a hardware frame pointer.

For assembly functions with Go prototypes, go vet will check that the argument namesand offsets match.On 32-bit systems, the low and high 32 bits of a 64-bit value are distinguished by addinga _lo or _hi suffix to the name, as in arg_lo+0(FP) or arg_hi+4(FP).If a Go prototype does not name its result, the expected assembly name is ret.

The SP pseudo-register is a virtual stack pointerused to refer to frame-local variables and the arguments beingprepared for function calls.It points to the highest address within the local stack frame, so references should use negative offsetsin the range [−framesize, 0):x-8(SP), y-4(SP), and so on.

On architectures with a hardware register named SP,the name prefix distinguishesreferences to the virtual stack pointer from references to the architecturalSP register.That is, x-8(SP) and -8(SP)are different memory locations:the first refers to the virtual stack pointer pseudo-register,while the second refers to thehardware's SP register.

On machines where SP and PC aretraditionally aliases for a physical, numbered register,in the Go assembler the names SP and PCare still treated specially;for instance, references to SP require a symbol,much like FP.To access the actual hardware register use the true R name.For example, on the ARM architecture the hardwareSP and PC are accessible asR13 and R15.

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Branches and direct jumps are always written as offsets to the PC, or asjumps to labels:

label:MOVW $0, R1JMP label

Each label is visible only within the function in which it is defined.It is therefore permitted for multiple functions in a file to defineand use the same label names.Direct jumps and call instructions can target text symbols,such as name(SB), but not offsets from symbols,such as name+4(SB).

Instructions, registers, and assembler directives are always in UPPER CASE to remind youthat assembly programming is a fraught endeavor.(Exception: the g register renaming on ARM.)

In Go object files and binaries, the full name of a symbol is thepackage path followed by a period and the symbol name:fmt.Printf or math/rand.Int.Because the assembler's parser treats period and slash as punctuation,those strings cannot be used directly as identifier names.Instead, the assembler allows the middle dot character U+00B7and the division slash U+2215 in identifiers and rewrites them toplain period and slash.Within an assembler source file, the symbols above are written asfmt·Printf and math∕rand·Int.The assembly listings generated by the compilers when using the -S flagshow the period and slash directly instead of the Unicode replacementsrequired by the assemblers.

Most hand-written assembly files do not include the full package pathin symbol names, because the linker inserts the package path of the currentobject file at the beginning of any name starting with a period:in an assembly source file within the math/rand package implementation,the package's Int function can be referred to as ·Int.This convention avoids the need to hard-code a package's import path in itsown source code, making it easier to move the code from one location to another.

Directives

The assembler uses various directives to bind text and data to symbol names.For example, here is a simple complete function definition. The TEXTdirective declares the symbol runtime·profileloop and the instructionsthat follow form the body of the function.The last instruction in a TEXT block must be some sort of jump, usually a RET (pseudo-)instruction.(If it's not, the linker will append a jump-to-itself instruction; there is no fallthrough in TEXTs.)After the symbol, the arguments are flags (see below)and the frame size, a constant (but see below):

TEXT runtime·profileloop(SB),NOSPLIT,$8MOVQ$runtime·profileloop1(SB), CXMOVQCX, 0(SP)CALLruntime·externalthreadhandler(SB)RET

In the general case, the frame size is followed by an argument size, separated by a minus sign.(It's not a subtraction, just idiosyncratic syntax.)The frame size $24-8 states that the function has a 24-byte frameand is called with 8 bytes of argument, which live on the caller's frame.If NOSPLIT is not specified for the TEXT,the argument size must be provided.For assembly functions with Go prototypes, go vet will check that theargument size is correct.

Note that the symbol name uses a middle dot to separate the components and is specified as an offset from thestatic base pseudo-register SB.This function would be called from Go source for package runtime using thesimple name profileloop.

Global data symbols are defined by a sequence of initializingDATA directives followed by a GLOBL directive.Each DATA directive initializes a section of thecorresponding memory.The memory not explicitly initialized is zeroed.The general form of the DATA directive is

DATAsymbol+offset(SB)/width, value

which initializes the symbol memory at the given offset and width with the given value.The DATA directives for a given symbol must be written with increasing offsets.

The GLOBL directive declares a symbol to be global.The arguments are optional flags and the size of the data being declared as a global,which will have initial value all zeros unless a DATA directivehas initialized it.The GLOBL directive must follow any corresponding DATA directives.

For example,

DATA divtab<>+0x00(SB)/4, $0xf4f8fcffDATA divtab<>+0x04(SB)/4, $0xe6eaedf0...DATA divtab<>+0x3c(SB)/4, $0x81828384GLOBL divtab<>(SB), RODATA, $64GLOBL runtime·tlsoffset(SB), NOPTR, $4

declares and initializes divtab<>, a read-only 64-byte table of 4-byte integer values,and declares runtime·tlsoffset, a 4-byte, implicitly zeroed variable thatcontains no pointers.

There may be one or two arguments to the directives.If there are two, the first is a bit mask of flags,which can be written as numeric expressions, added or or-ed together,or can be set symbolically for easier absorption by a human.Their values, defined in the standard #include file textflag.h, are:

  • NOPROF = 1
    (For TEXT items.)Don't profile the marked function. This flag is deprecated.
  • DUPOK = 2
    It is legal to have multiple instances of this symbol in a single binary.The linker will choose one of the duplicates to use.
  • NOSPLIT = 4
    (For TEXT items.)Don't insert the preamble to check if the stack must be split.The frame for the routine, plus anything it calls, must fit in thespare space remaining in the current stack segment.Used to protect routines such as the stack splitting code itself.
  • RODATA = 8
    (For DATA and GLOBL items.)Put this data in a read-only section.
  • NOPTR = 16
    (For DATA and GLOBL items.)This data contains no pointers and therefore does not need to bescanned by the garbage collector.
  • WRAPPER = 32
    (For TEXT items.)This is a wrapper function and should not count as disabling recover.
  • NEEDCTXT = 64
    (For TEXT items.)This function is a closure so it uses its incoming context register.
  • LOCAL = 128
    This symbol is local to the dynamic shared object.
  • TLSBSS = 256
    (For DATA and GLOBL items.)Put this data in thread local storage.
  • NOFRAME = 512
    (For TEXT items.)Do not insert instructions to allocate a stack frame and save/restore the returnaddress, even if this is not a leaf function.Only valid on functions that declare a frame size of 0.
  • TOPFRAME = 2048
    (For TEXT items.)Function is the outermost frame of the call stack. Traceback should stop at this function.

Interacting with Go types and constants

If a package has any .s files, then go build will directthe compiler to emit a special header called go_asm.h,which the .s files can then #include.The file contains symbolic #define constants for theoffsets of Go struct fields, the sizes of Go struct types, and mostGo const declarations defined in the current package.Go assembly should avoid making assumptions about the layout of Gotypes and instead use these constants.This improves the readability of assembly code, and keeps it robust tochanges in data layout either in the Go type definitions or in thelayout rules used by the Go compiler.

Constants are of the form const_name.For example, given the Go declaration const bufSize =1024, assembly code can refer to the value of this constantas const_bufSize.

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Field offsets are of the form type_field.Struct sizes are of the form type__size.For example, consider the following Go definition:

type reader struct {buf [bufSize]byter int}

Assembly can refer to the size of this structas reader__size and the offsets of the two fieldsas reader_buf and reader_r.Hence, if register R1 contains a pointer toa reader, assembly can reference the r fieldas reader_r(R1).

If any of these #define names are ambiguous (for example,a struct with a _size field), #include"go_asm.h" will fail with a "redefinition of macro" error.

Runtime Coordination

For garbage collection to run correctly, the runtime must know thelocation of pointers in all global data and in most stack frames.The Go compiler emits this information when compiling Go source files,but assembly programs must define it explicitly.

A data symbol marked with the NOPTR flag (see above)is treated as containing no pointers to runtime-allocated data.A data symbol with the RODATA flagis allocated in read-only memory and is therefore treatedas implicitly marked NOPTR.A data symbol with a total size smaller than a pointeris also treated as implicitly marked NOPTR.It is not possible to define a symbol containing pointers in an assembly source file;such a symbol must be defined in a Go source file instead.Assembly source can still refer to the symbol by nameeven without DATA and GLOBL directives.A good general rule of thumb is to define all non-RODATAsymbols in Go instead of in assembly.

Each function also needs annotations giving the location oflive pointers in its arguments, results, and local stack frame.For an assembly function with no pointer results andeither no local stack frame or no function calls,the only requirement is to define a Go prototype for the functionin a Go source file in the same package. The name of the assemblyfunction must not contain the package name component (for example,function Syscall in package syscall shoulduse the name ·Syscall instead of the equivalent namesyscall·Syscall in its TEXT directive).For more complex situations, explicit annotation is needed.These annotations use pseudo-instructions defined in the standard#include file funcdata.h.

If a function has no arguments and no results,the pointer information can be omitted.This is indicated by an argument size annotation of $n-0on the TEXT instruction.Otherwise, pointer information must be provided bya Go prototype for the function in a Go source file,even for assembly functions not called directly from Go.(The prototype will also let go vet check the argument references.)At the start of the function, the arguments are assumedto be initialized but the results are assumed uninitialized.If the results will hold live pointers during a call instruction,the function should start by zeroing the results and thenexecuting the pseudo-instruction GO_RESULTS_INITIALIZED.This instruction records that the results are now initializedand should be scanned during stack movement and garbage collection.It is typically easier to arrange that assembly functions do notreturn pointers or do not contain call instructions;no assembly functions in the standard library useGO_RESULTS_INITIALIZED.

If a function has no local stack frame,the pointer information can be omitted.This is indicated by a local frame size annotation of $0-non the TEXT instruction.The pointer information can also be omitted if thefunction contains no call instructions.Otherwise, the local stack frame must not contain pointers,and the assembly must confirm this fact by executing thepseudo-instruction NO_LOCAL_POINTERS.Because stack resizing is implemented by moving the stack,the stack pointer may change during any function call:even pointers to stack data must not be kept in local variables.

Assembly functions should always be given Go prototypes,both to provide pointer information for the arguments and resultsand to let go vet check thatthe offsets being used to access them are correct.

Architecture-specific details

It is impractical to list all the instructions and other details for each machine.To see what instructions are defined for a given machine, say ARM,look in the source for the obj support library forthat architecture, located in the directory src/cmd/internal/obj/arm.In that directory is a file a.out.go; it containsa long list of constants starting with A, like this:

const (AAND = obj.ABaseARM + obj.A_ARCHSPECIFIC + iotaAEORASUBARSBAADD...

This is the list of instructions and their spellings as known to the assembler and linker for that architecture.Each instruction begins with an initial capital A in this list, so AANDrepresents the bitwise and instruction,AND (without the leading A),and is written in assembly source as AND.The enumeration is mostly in alphabetical order.(The architecture-independent AXXX, defined in thecmd/internal/obj package,represents an invalid instruction).The sequence of the A names has nothing to do with the actualencoding of the machine instructions.The cmd/internal/obj package takes care of that detail.

The instructions for both the 386 and AMD64 architectures are listed incmd/internal/obj/x86/a.out.go.

The architectures share syntax for common addressing modes such as(R1) (register indirect),4(R1) (register indirect with offset), and$foo(SB) (absolute address).The assembler also supports some (not necessarily all) addressing modesspecific to each architecture.The sections below list these.

One detail evident in the examples from the previous sections is that data in the instructions flows from left to right:MOVQ $0, CX clears CX.This rule applies even on architectures where the conventional notation uses the opposite direction.

Here follow some descriptions of key Go-specific details for the supported architectures.

32-bit Intel 386

The runtime pointer to the g structure is maintainedthrough the value of an otherwise unused (as far as Go is concerned) register in the MMU.In the runtime package, assembly code can include go_tls.h, which definesan OS- and architecture-dependent macro get_tls for accessing this register.The get_tls macro takes one argument, which is the register to load theg pointer into.

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For example, the sequence to load g and musing CX looks like this:

#include "go_tls.h"#include "go_asm.h"...get_tls(CX)MOVLg(CX), AX // Move g into AX.MOVLg_m(AX), BX // Move g.m into BX.

The get_tls macro is also defined on amd64.

Addressing modes:

  • (DI)(BX*2): The location at address DI plus BX*2.
  • 64(DI)(BX*2): The location at address DI plus BX*2 plus 64.These modes accept only 1, 2, 4, and 8 as scale factors.

When using the compiler and assembler's-dynlink or -shared modes,any load or store of a fixed memory location such as a global variablemust be assumed to overwrite CX.Therefore, to be safe for use with these modes,assembly sources should typically avoid CX except between memory references.

64-bit Intel 386 (a.k.a. amd64)

The two architectures behave largely the same at the assembler level.Assembly code to access the m and gpointers on the 64-bit version is the same as on the 32-bit 386,except it uses MOVQ rather than MOVL:

get_tls(CX)MOVQg(CX), AX // Move g into AX.MOVQg_m(AX), BX // Move g.m into BX.

Register BP is callee-save.The assembler automatically inserts BP save/restore when frame size is larger than zero.Using BP as a general purpose register is allowed,however it can interfere with sampling-based profiling.

ARM

The registers R10 and R11are reserved by the compiler and linker.

R10 points to the g (goroutine) structure.Within assembler source code, this pointer must be referred to as g;the name R10 is not recognized.

To make it easier for people and compilers to write assembly, the ARM linkerallows general addressing forms and pseudo-operations like DIV or MODthat may not be expressible using a single hardware instruction.It implements these forms as multiple instructions, often using the R11 registerto hold temporary values.Hand-written assembly can use R11, but doing so requiresbeing sure that the linker is not also using it to implement any of the otherinstructions in the function.

When defining a TEXT, specifying frame size $-4tells the linker that this is a leaf function that does not need to save LR on entry.

The name SP always refers to the virtual stack pointer described earlier.For the hardware register, use R13.

Condition code syntax is to append a period and the one- or two-letter code to the instruction,as in MOVW.EQ.Multiple codes may be appended: MOVM.IA.W.The order of the code modifiers is irrelevant.

Addressing modes:

  • R0->16
    R0>>16
    R0<<16
    R0@>16:For <<, left shift R0 by 16 bits.The other codes are -> (arithmetic right shift),>> (logical right shift), and@> (rotate right).
  • R0->R1
    R0>>R1
    R0<<R1
    R0@>R1:For <<, left shift R0 by the count in R1.The other codes are -> (arithmetic right shift),>> (logical right shift), and@> (rotate right).
  • [R0,g,R12-R15]: For multi-register instructions, the set comprisingR0, g, and R12 through R15 inclusive.
  • (R5, R6): Destination register pair.

ARM64

R18 is the "platform register", reserved on the Apple platform.To prevent accidental misuse, the register is named R18_PLATFORM.R27 and R28 are reserved by the compiler and linker.R29 is the frame pointer.R30 is the link register.

Instruction modifiers are appended to the instruction following a period.The only modifiers are P (postincrement) and W(preincrement):MOVW.P, MOVW.W

Addressing modes:

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  • R0->16
    R0>>16
    R0<<16
    R0@>16:These are the same as on the 32-bit ARM.
  • $(8<<12):Left shift the immediate value 8 by 12 bits.
  • 8(R0):Add the value of R0 and 8.
  • (R2)(R0):The location at R0 plus R2.
  • R0.UXTB
    R0.UXTB<<imm:UXTB: extract an 8-bit value from the low-order bits of R0 and zero-extend it to the size of R0.R0.UXTB<<imm: left shift the result of R0.UXTB by imm bits.The imm value can be 0, 1, 2, 3, or 4.The other extensions include UXTH (16-bit), UXTW (32-bit), and UXTX (64-bit).
  • R0.SXTB
    R0.SXTB<<imm:SXTB: extract an 8-bit value from the low-order bits of R0 and sign-extend it to the size of R0.R0.SXTB<<imm: left shift the result of R0.SXTB by imm bits.The imm value can be 0, 1, 2, 3, or 4.The other extensions include SXTH (16-bit), SXTW (32-bit), and SXTX (64-bit).
  • (R5, R6): Register pair for LDAXP/LDP/LDXP/STLXP/STP/STP.

Reference: Go ARM64 Assembly Instructions Reference Manual

PPC64

This assembler is used by GOARCH values ppc64 and ppc64le.

Reference: Go PPC64 Assembly Instructions Reference Manual

IBM z/Architecture, a.k.a. s390x

The registers R10 and R11 are reserved.The assembler uses them to hold temporary values when assembling some instructions.

R13 points to the g (goroutine) structure.This register must be referred to as g; the name R13 is not recognized.

R15 points to the stack frame and should typically only be accessed using thevirtual registers SP and FP.

Load- and store-multiple instructions operate on a range of registers.The range of registers is specified by a start register and an end register.For example, LMG (R9), R5, R7 would loadR5, R6 and R7 with the 64-bit values at0(R9), 8(R9) and 16(R9) respectively.

Storage-and-storage instructions such as MVC and XC are writtenwith the length as the first argument.For example, XC $8, (R9), (R9) would cleareight bytes at the address specified in R9.

If a vector instruction takes a length or an index as an argument then it will be thefirst argument.For example, VLEIF $1, $16, V2 will loadthe value sixteen into index one of V2.Care should be taken when using vector instructions to ensure that they are available atruntime.To use vector instructions a machine must have both the vector facility (bit 129 in thefacility list) and kernel support.Without kernel support a vector instruction will have no effect (it will be equivalentto a NOP instruction).

Addressing modes:

  • (R5)(R6*1): The location at R5 plus R6.It is a scaled mode as on the x86, but the only scale allowed is 1.

MIPS, MIPS64

General purpose registers are named R0 through R31,floating point registers are F0 through F31.

R30 is reserved to point to g.R23 is used as a temporary register.

In a TEXT directive, the frame size $-4 for MIPS or$-8 for MIPS64 instructs the linker not to save LR.

SP refers to the virtual stack pointer.For the hardware register, use R29.

Addressing modes:

  • 16(R1): The location at R1 plus 16.
  • (R1): Alias for 0(R1).

The value of GOMIPS environment variable (hardfloat orsoftfloat) is made available to assembly code by predefining eitherGOMIPS_hardfloat or GOMIPS_softfloat.

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The value of GOMIPS64 environment variable (hardfloat orsoftfloat) is made available to assembly code by predefining eitherGOMIPS64_hardfloat or GOMIPS64_softfloat.

Unsupported opcodes

The assemblers are designed to support the compiler so not all hardware instructionsare defined for all architectures: if the compiler doesn't generate it, it might not be there.If you need to use a missing instruction, there are two ways to proceed.One is to update the assembler to support that instruction, which is straightforwardbut only worthwhile if it's likely the instruction will be used again.Instead, for simple one-off cases, it's possible to use the BYTEand WORD directivesto lay down explicit data into the instruction stream within a TEXT.Here's how the 386 runtime defines the 64-bit atomic load function.

// uint64 atomicload64(uint64 volatile* addr);// so actually// void atomicload64(uint64 *res, uint64 volatile *addr);TEXT runtime·atomicload64(SB), NOSPLIT, $0-12MOVLptr+0(FP), AXTESTL$7, AXJZ2(PC)MOVL0, AX // crash with nil ptr derefLEALret_lo+4(FP), BX// MOVQ (%EAX), %MM0BYTE $0x0f; BYTE $0x6f; BYTE $0x00// MOVQ %MM0, 0(%EBX)BYTE $0x0f; BYTE $0x7f; BYTE $0x03// EMMSBYTE $0x0F; BYTE $0x77RET

FAQs

What language is the Go compiler in? ›

It's written in C. The libraries are written in Go itself.

Is Go compiled to assembly? ›

The problem is that the Go compiler does not generate actual assembly. It generates something that looks a lot like assembly but contains a lot of pseudo-instructions that will be expanded by the linker. Only after linking is done, actual assembly is produced (and immediately assembled).

How does the Go compiler work? ›

Go is a compiled language

compiled language
A compiled language is a programming language whose implementations are typically compilers (translators that generate machine code from source code), and not interpreters (step-by-step executors of source code, where no pre-runtime translation takes place).
https://en.wikipedia.org › wiki › Compiled_language
. This means we must run our source code files through a compiler, which reads source code and generates a binary, or executable, file that is used to run the program. Examples of other popular compiled languages include C, C++, and Swift.

Does Go need a runtime? ›

Does Go have a runtime? Go does have an extensive library, called the runtime, that is part of every Go program. The runtime library implements garbage collection, concurrency, stack management, and other critical features of the Go language.

Is Go worth learning? ›

Is Golang Worth Learning in 2022? Yes, Golang is still worth learning in 2022 as it has experienced an increase in popularity among developers. According to Stack Overflow's 2020 Developer Survey , Golang moved up to fifth place from ninth place in 2019 on the most loved languages list.

Is Golang hard to learn? ›

Easy to Learn

Since the syntax of Golang is somewhat similar to the C-language, it is easy to pick up, especially for C-style or Java programmers. The syntax of Go is smaller as compared to a lot of other programming languages and has an only minimalistic set of features to get the task done.

Is rust better than Go? ›

For all of the tested algorithms, the most optimized Rust code was at least 30 percent faster than the most optimized Go code, and in many cases it was significantly more; for the binary-trees benchmark, the most optimized Rust code was 12 times faster than the most optimized Go code!

Is Go like C++? ›

While Go and C++ both compile directly to binary code, it's easy to make the case that Go is “higher-level” than C++ because it contains a runtime in each executable program that manages memory and performs basic administrative tasks “under the hood”.

Is Go faster than C++? ›

Go was created with the user in mind. Go syntax is easy to understand, and it compiles faster than C++. C++ shows excellent performance due to its closeness to machine code and OOP support. Go beats most high-level languages in performance.

How long will it take to learn Golang? ›

Time taken to learn a language depends from person to person. But if you are an expert of one back-end programming language like Java, Python, Php, C then it is going to be very easy for you. So if you want to cover the basics of Golang then will take around 10-15 days for you to become familiar with the Golang.

Why is Golang so fast? ›

Go is Fast

Because Go is compiled

compiled
A compiled language is a programming language whose implementations are typically compilers (translators that generate machine code from source code), and not interpreters (step-by-step executors of source code, where no pre-runtime translation takes place).
https://en.wikipedia.org › wiki › Compiled_language
to machine code, it will naturally outperform languages that are interpreted or have virtual runtimes. Go programs also compile extremely fast, and the resulting binary is very small. Our API compiles in seconds and produces an executable file that is 11.5 MB.

Is Go functional or OOP? ›

Go (or “Golang”) is a post-OOP programming language that borrows its structure (packages, types, functions) from the Algol/Pascal/Modula language family. Nevertheless, in Go, object-oriented patterns are still useful for structuring a program in a clear and understandable way.

Is Golang worth learning 2022? ›

So, yes, definitely Golang is worth learning in 2022 and beyond. Learning Golang or Gol Programming language can boost your career and also help you to get a job at Google, which is the dream of many software developers.

Will Golang replace Java? ›

No, it is not likely that Golang will replace Java. Golang is a newer language that has gained popularity in recent years, while Java is a more established language that is still widely used today. They both have their strengths and weaknesses just like any programming language.

Why Golang is not popular? ›

It makes language learning very easy and fast. However, on the other hand, sometimes developers lack some features that they have in other languages and, therefore, they need to code workarounds or write more code in the long run. Unfortunately, Go lacks a lot of features by design, and sometimes it's really annoying.

Should I learn Python or Golang 2022? ›

When it comes to microservices, APIs, and other fast-load features, Golang is absolutely better than Python. But when it comes to natural language processing or machine learning, the robustness and readability of Python (as well as the extensiveness of its libraries) come into play.

Should I learn Golang or Java 2022? ›

The decision between both should rely on the needs of the website. Java is an ancient but widely used programming language. But, GO is a young but technically advanced programming language. Both are ideal for constructing result-oriented applications.

Can Golang replace Python? ›

That's a hell YES! Golang can replace python as the server-side language for building concurrent services. Developers need to choose a programming language considering their nature and size of the development project.

Can you get a job with Golang? ›

Golang (also called Go) is an in-demand programming language, especially for people working with Google products. Go is used by many big companies, like Uber Medium, Dropbox, Salesforce, Netflix, IBM, and Twitter. Go is a great option for job seekers of all levels.

Is Python or Go easier? ›

Answer: Python is easy. Though Python does not manage to be both quick and simple, but it is not slow and challenging either. It is a comparatively simple language, only less accessible than Go is. The free libraries of Python and commonly used tutorials make it effortless to learn.

Which is better Go or Python? ›

Multiple tests show that Go runs up to 30 times faster than Python. Thanks to Go's support for concurrency, it executes calculations significantly faster compared to Python. Go vs Python performance: Golang wins.

What is Golang best for? ›

What is Golang Useful for? Golang is useful for carrying out programming for scalable servers and large software systems. The Golang programming language was built to fill in the gaps of C++ and Java that Google came across while working with its servers and distributed systems.

What is fastest programming language? ›

C++ C++ is one of the most efficient and fastest languages. It is widely used by competitive programmers for its execution speed and Standard Template Libraries(STL).

Why is Go so good? ›

Go is a really flexible language, able to solve a lot of problems. You can use it for system and network programming, big data, machine learning, audio and video editing, and more.

Is Golang good for backend? ›

Where Golang Fits. Go makes an ideal choice for backend web development, particularly for high-performing concurrent services on the server side. It can be used for building the server side of your mobile app too. For instance, the GUI part of an Android app can be written in Java while the app backend can use Golang.

Is Java faster than Golang? ›

Even though Java is quick, Golang outperforms Java in most metrics. Java's lack of performance is partly due to its virtual machine for Java compilation. Though it allows Java to run on any platform, this virtual machine reduces its speed. Golang has the upper hand.

Why is Golang popular? ›

Go or Golang attempts to reclaim the memory occupied by other objects that are no longer needed which makes Go a highly garbage collected language. It is also a very lightweight language which comes with good support for concurrency. While this is not a direct technical advantage, Go is supported by Google.

Who uses Golang? ›

List of Go Companies: Overview
Companies That Use GoWho Uses Go at This Company?
Capital OneAutomation engineer, database developer, cloud engineer
DropboxAutomation engineer, infrastructure engineer, machine learning engineer
Riot GamesDevOps engineer, infrastructure engineer, platform engineer
7 more rows
9 Feb 2022

Is Go like Python? ›

Go is a Procedural, functional and concurrent language while Python is an object-oriented, imperative, functional, and procedural language. Go supports concurrency, on the other hand Python, doesn't have any in-built concurrency mechanism.

Is Golang better than C? ›

Go is fast

Go binaries run more slowly than their C counterparts, but the difference in speed is negligible for most applications. Go performance is as good as C for the vast majority of work, and generally much faster than other languages known for speed of development (e.g., JavaScript, Python, and Ruby).

Is Golang good for beginners? ›

Go is a simple language to learn, especially for beginners

Go is a great language for beginners, and just in general, because the syntax is small - you won't have to spend ages paging through reference documentation. It's clean and easy to read, meaning you'll be able to understand what you and others are writing.

What's the best way to learn Go? ›

10 Best online training Courses to learn Golang in 2022
  1. Go: The Complete Developer's Guide (Golang) — Udemy. ...
  2. Go Programming (Golang): The Complete Developer's Guide. ...
  3. Programming with Google Go Specialization (Coursera) ...
  4. Go Fundamentals By Nigel Poulton (Pluralsight) ...
  5. Learn Go on Codecademy.

Where can I learn Golang for free? ›

10 Free Resources To Learn Go Programming Language
  • 1| Golang Documentation.
  • 2| An Introduction To Programming In Go.
  • 3| Go By Example.
  • 4| The Little Go Book.
  • 5| 50 Shades Of Go.
  • 6| Golangbot Tutorial.
  • 7| Go Tutorial.
  • 8| Learning Go.
8 Aug 2019

Is Golang popular in 2022? ›

In 2022, Golang will continue to be a popular choice for web development and will be a great option for building fast, reliable, and efficient software. If you're looking for a language that is efficient, easy to learn, and reliable, then Golang is a great choice for your web development projects in 2022.

What can I build with Golang? ›

Golang's Versatility

Built for speed and born in the cloud, Go is a programming language that developers can leverage to create everything from web applications and microservices to cloud-native apps and machine learning solutions.

Is Golang front end or back end? ›

Go, also called Golang, is an open source, statically typed, compiled, cross-platform, and lightning fast programming language first introduced by Google in 2009. Go is multi-purpose, it is a good language for backend development.

What type of language is Go? ›

Go (also called Golang or Go language) is an open source programming language used for general purpose. Go was developed by Google engineers to create dependable and efficient software. Most similarly modeled after C, Go is statically typed and explicit.

What language is Golang similar to? ›

Java. The next alternative to the Golang language is known as Java. Again, this alternative to Go is object-centered and has a quite simple structure.

Why did Google create Golang? ›

History. Go was designed at Google in 2007 to improve programming productivity in an era of multicore, networked machines and large codebases. The designers wanted to address criticism of other languages in use at Google, but keep their useful characteristics: Static typing and run-time efficiency (like C)

Is Go based on C? ›

Go is influenced by C (especially the Plan 9 dialect), but with an emphasis on greater simplicity and safety.

Is Go implemented in C? ›

Golang was formerly written in C but is now written in Go itself. As of December 2013, the Go team announced their transitioning of the compiler to Go. Since February 2015 the implementation of C has been deleted and the compiler is now self-hosting, with the new compiler first introduced in Go 1.5.

What type of language is Go? ›

Go (also called Golang or Go language) is an open source programming language used for general purpose. Go was developed by Google engineers to create dependable and efficient software. Most similarly modeled after C, Go is statically typed and explicit.

Is Go faster than C++? ›

Compile time is dependent on what you're coding, however, C++ is famous for its slow compile time. Go's compact style makes compiling quicker than C++'s long drawn-out form. Overall, Golang beats C++ hands down when it comes to coding speed.

Is Golang like Python? ›

Python is a language that is typed dynamically, and Golang is the one that is typed statically. While Python uses an interpreter, Golang uses a compiler for the execution.

Does Google use Golang? ›

Google uses Go (in conjunction with the Google Cloud offerings) to develop clusters, this includes using Kubernetes, Docker, and other containerized solutions.

Does Facebook use Golang? ›

Here are some notable companies that have shifted to using Golang: Google. Apple. Facebook.

Is Golang OOP or functional? ›

Go (or “Golang”) is a post-OOP programming language that borrows its structure (packages, types, functions) from the Algol/Pascal/Modula language family. Nevertheless, in Go, object-oriented patterns are still useful for structuring a program in a clear and understandable way.

Will Golang replace Java? ›

No, it is not likely that Golang will replace Java. Golang is a newer language that has gained popularity in recent years, while Java is a more established language that is still widely used today. They both have their strengths and weaknesses just like any programming language.

Is Golang the future? ›

So, yes, definitely Golang is worth learning in 2022 and beyond. Learning Golang or Gol Programming language can boost your career and also help you to get a job at Google, which is the dream of many software developers.

Is Go good for beginners? ›

Of the options covered so far, Go is by far the best starting point for beginners. Assembly requires too much patience.

Is Go front end or backend? ›

Go, also called Golang, is an open source, statically typed, compiled, cross-platform, and lightning fast programming language first introduced by Google in 2009. Go is multi-purpose, it is a good language for backend development.

Does Netflix use Golang? ›

Netflix Uses Golang For Rend Proxy.

Why is Golang so fast? ›

Go is Fast

Because Go is compiled

compiled
A compiled language is a programming language whose implementations are typically compilers (translators that generate machine code from source code), and not interpreters (step-by-step executors of source code, where no pre-runtime translation takes place).
https://en.wikipedia.org › wiki › Compiled_language
to machine code, it will naturally outperform languages that are interpreted or have virtual runtimes. Go programs also compile extremely fast, and the resulting binary is very small. Our API compiles in seconds and produces an executable file that is 11.5 MB.

How long does it take to learn Golang? ›

How Long Does It Take to Learn Golang? If you already know C or Java, Golang is easy to learn, and you can start writing programs in just a few days. If you do not know C or Java, it will take you two to three months to learn to use Golang professionally.

Is Golang good for backend? ›

Where Golang Fits. Go makes an ideal choice for backend web development, particularly for high-performing concurrent services on the server side. It can be used for building the server side of your mobile app too. For instance, the GUI part of an Android app can be written in Java while the app backend can use Golang.

Videos

1. GO assembler
(Gheorghe Curelet-Balan)
2. #227 Running GoLang on an STM32 MCU. Why and how. // Tutorial
(MickMake)
3. Introduction to Golang. Why Golang?
(Steve Hook)
4. The Go Programming Language
(Google TechTalks)
5. Google I/O 2012 - Meet the Go Team
(Google Developers)
6. Let's Golang by Pallat Anchaleechamaikorn
(ODDS team)

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