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2 .Go toolchain overview
A toolchain is a package composed of the compiler and ancillary
tools, libraries and runtime for a language which together allow you
to build and run code written in that language.
• gc: evolved from the Plan 9 toolchain and includes its own compiler, assembler, linker
and tools, as well as the Go runtime and standard library.
• gccgo: extends the gcc project to support Go.
• llgo: built on top of the LLVM compiler infrastructure.
2 © 2018 Arm Limited
3 .Go toolchain example
$go build -x helloworld.go
……
/golang/pkg/tool/linux_arm64/compile -o $WORK/b001/_pkg_.a -trimpath $WORK/b001 -p main -complete -buildid
Lz0Z4IaaV-BMteKblcuy/Lz0Z4IaaV-BMteKblcuy -D _/golang/test -importcfg $WORK/b001/importcfg -pack -c=4
./helloworld.go
/golang/pkg/tool/linux_arm64/buildid -w $WORK/b001/_pkg_.a # internal
……
/golang/pkg/tool/linux_arm64/link -o $WORK/b001/exe/a.out -importcfg $WORK/b001/importcfg.link -
buildmode=exe -buildid=C4PaIvbSKZNsCh5tSi2r/Lz0Z4IaaV-BMteKblcuy/fOp-
Rk_DpGJ5cJq23wER/C4PaIvbSKZNsCh5tSi2r -extld=gcc $WORK/b001/_pkg_.a
/golang/pkg/tool/linux_arm64/buildid -w $WORK/b001/exe/a.out # internal
mv $WORK/b001/exe/a.out helloworld
3 © 2018 Arm Limited
4 .Go toolchain workflow
$ go tool *.go compile $WORK/b001/_pkg_.a
addr2line
api
asm
buildid
cgo
compile *.s asm *.o pack runtime=$WORK/b002/_pkg_.a
cover
dist link helloworld
doc
fix
link internal/bytealg=$WORK/b003/_pkg_.a
nm
objdump
pack
pprof ……
test2json
trace
vet
4 © 2018 Arm Limited
5 .Compile
© 2018 Arm Limited
6 .Go compiler overview
GCC LLVM
6 © 2018 Arm Limited
7 .Front end
• Syntax check
• Type check
• Dead code elimination
• Inline
• Escape analysis
• Declared and not used check
• Rewrite
• Instrument
7 © 2018 Arm Limited
8 .Middle end
Machine-independent Passes
Options providing insight into compiler decisions:
• -d=ssa/<phase>/stats
• -m
8 © 2018 Arm Limited
9 .Machine-independent optimization example
Div64 Sub64
Rsh64x64 Rsh64x64
Arg {a} Const64 [7]
Hmul64 Const64 [1]
Const64 Arg {a} Const64 [63]
[5270498306774157605]
a/7 (((a* 5270498306774157605)>>64)>>1)-(a>>63)
9 © 2018 Arm Limited
10 .Back end
Machine-dependent Passes
10 © 2018 Arm Limited
11 .Convert to machine-dependent ops
Example for arm64
Before After
410 Div <T> 428 Div <T>
411 b1: 429 b1:
412 v1 = InitMem <mem> 430 v1 = InitMem <mem>
413 v2 = SP <uintptr> 431 v2 = SP <uintptr>
414 v5 = Addr <*int64> {~r1} v2 433 v6 = Arg <int64> {a}
415 v6 = Arg <int64> {a} 434 v10 = VarDef <mem> {~r1} v1
416 v10 = VarDef <mem> {~r1} v1 435 v3 = MOVDconst <uint64> [5270498306774157605]
417 v3 = Const64 <uint64> [5270498306774157605] 443 v4 = MULH <int64> v3 v6
418 v12 = Const64 <uint64> [1] 444 v7 = SRAconst <int64> [1] v4
419 v14 = Const64 <uint64> [63] 445 v9 = SUBshiftRA <int64> [63] v7 v6
420 v4 = Hmul64 <int64> v3 v6 446 v11 = MOVDstore <mem> {~r1} v2 v9 v10
421 v13 = Rsh64x64 <int64> v6 v14 447 Ret v11
422 v7 = Rsh64x64 <int64> v4 v12
423 v9 = Sub64 <int64> v7 v13
424 v11 = Store <mem> {int64} v5 v9 v10
425 Ret v11
11 © 2018 Arm Limited
12 .Generate Prog
Prog describes a single “machine” instruction
722 00000 (3) TEXT "".Div(SB)
……
725 v19 00003 (4) MOVD $5270498306774157605, R0
726 v18 00004 (4) MOVD "".a(RSP), R1
727 v4 00005 (4) SMULH R1, R0, R0
728 v7 00006 (4) ASR $1, R0, R0
729 v9 00007 (4) SUB R1->63, R0, R0
730 v11 00008 (4) MOVD R0, "".~r1+8(RSP)
731 b1 00009 (4) RET
732 00010 (?) END
12 © 2018 Arm Limited
13 .Asm
© 2018 Arm Limited
14 .Go assembler overview
compile
Flushplist WriteObjFile goobj
Magic header
asm Parse linkpatch Version
Arch.Progedit Autolib
lex Arch.Preprocess Symbol references
operand Arch.Assemble Lengths
linkpcln Data block
pseudo
populateDWARF Symbols
instruction Magic footer
14 © 2018 Arm Limited
15 .Go arm64 assembly example
1 // func Add(a, b int) int
2 TEXT ·Add(SB),$0-24 Semi-abstract instruction set
3 MOVD arg1+0(FP), R0
4 MOVD arg2+8(FP), R1
5 ADD R1, R0, R0
6 MOVD R0, ret+16(FP)
7 RET
15 © 2018 Arm Limited
16 .Goobj
ELF
16 © 2018 Arm Limited
17 .Link
© 2018 Arm Limited
18 .Go link overview
_/golang/test (testmain)=$WORK/b001/_pkg_.a
runtime=$WORK/b002/_pkg_.a
runtime/cgo=$WORK/b008/_pkg_.a
compile
internal
internal/bytealg=$WORK/b003/_pkg_.a
Go
link a.out
runtime/internal/atomic=$WORK/b006/_pkg_.a
external
runtime/internal/sys=$WORK/b007/_pkg_.a
cgo $CC a.out
internal/cpu=$WORK/b004/_pkg_.a
……
C _x001.o
$CC _x002.o _/golang/test =$WORK/b048/_pkg_.a
_x003.o
18 © 2018 Arm Limited
19 .Go link workflow
1. Load package libraries and objects (including host objects)
2. Determine link mode
3. Mark all reachable symbols
4. Prepare ELF symbols (e.g set up PLT)
5. Assign addresses to text
6. Reorganize Go meta data (pcln, functab, type and …)
7. Handle relocations of host objects (if internal link)
8. Assign addresses to data
9. Generate DWARF (set up the per-compilation unit part of the DIE tree)
10. Resolve relocations (target dependent)
11. Write out ELF (code, data, table, header and …)
12. Emit relocations for host link (if external link)
13. Check undefined symbols
14. Invoke host link to generate output (if external link)
15. Invoke host ar to generate output (if C Archive)
19 © 2018 Arm Limited
20 .Others
© 2018 Arm Limited
21 .Some interesting topics
• VGo: Go += Package Versioning
• WebAssembly architecture
• Safe-points everywhere
• Register-based calling convention
• Mid-stack inlining
• ……
21 © 2018 Arm Limited
22 . Thank You!
Danke!
Merci!
!
!
Gracias!
Kiitos!
감사합니다
ध"यवाद
22 © 2018 Arm Limited
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