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mkevac opened this issue Dec 8, 2016 · 6 comments
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cmd/objdump: print Go code alongside assembly #18245

mkevac opened this issue Dec 8, 2016 · 6 comments
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FrozenDueToAge help wanted Proposal-Accepted Suggested Issues that may be good for new contributors looking for work to do.
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@mkevac
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mkevac commented Dec 8, 2016

I would like a way to get disassembly with corresponding Go code. Similar to what objdump -S does, but with Go assembly.

$ objdump -S testif.test
[...]
	if m == hash[h] {
  40c41c:	89 da                	mov    %ebx,%edx
  40c41e:	48 81 fa f1 03 00 00 	cmp    $0x3f1,%rdx
  40c425:	0f 83 55 01 00 00    	jae    40c580 <runtime.additab+0x3f0>
  40c42b:	48 8d 05 ae 80 1e 00 	lea    0x1e80ae(%rip),%rax        # 5f44e0 <runtime.hash>
  40c432:	48 8b 1c d0          	mov    (%rax,%rdx,8),%rbx
  40c436:	48 8d 04 d0          	lea    (%rax,%rdx,8),%rax
  40c43a:	48 89 84 24 b8 00 00 	mov    %rax,0xb8(%rsp)
  40c441:	00 
  40c442:	48 39 d9             	cmp    %rbx,%rcx
  40c445:	74 50                	je     40c497 <runtime.additab+0x307>
		println("duplicate itab for", typ.string(), "and", inter.typ.string())
		throw("duplicate itabs")
	}
	m.link = hash[h]
  40c447:	8b 15 13 14 20 00    	mov    0x201413(%rip),%edx        # 60d860 <runtime.writeBarrier>
  40c44d:	48 8d 71 10          	lea    0x10(%rcx),%rsi
  40c451:	85 d2                	test   %edx,%edx
  40c453:	75 22                	jne    40c477 <runtime.additab+0x2e7>
  40c455:	48 89 59 10          	mov    %rbx,0x10(%rcx)
	atomicstorep(unsafe.Pointer(&hash[h]), unsafe.Pointer(m))
  40c459:	48 89 04 24          	mov    %rax,(%rsp)
  40c45d:	48 89 4c 24 08       	mov    %rcx,0x8(%rsp)
  40c462:	e8 29 5b ff ff       	callq  401f90 <runtime.atomicstorep>
[...]

I propose that we add -S to go tool objdump.

The only way I know to get similar thing is to use weblist command in go tool pprof. But you need profile data for that.

$ go version
go version devel +d4b46aa Thu Dec 8 01:36:44 2016 +0000 linux/amd64
@bradfitz bradfitz added this to the Proposal milestone Dec 8, 2016
@bradfitz bradfitz changed the title Print Go assembly with corresponding Go code in between proposal: cmd/objdump: print Go code alongside assembly Dec 8, 2016
@rsc rsc modified the milestones: Unplanned, Proposal Dec 12, 2016
@rsc
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rsc commented Dec 12, 2016

This seems like a reasonable addition. If you (or anyone else) would like to send a CL, please do.

@bradfitz bradfitz added help wanted Suggested Issues that may be good for new contributors looking for work to do. labels Dec 12, 2016
@ALTree
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ALTree commented Dec 15, 2016 •
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I've poked around in cmd/internal/objfile (which objdump uses to disassemble) and it looks like it shouldn't be too hard to add some support for -S in objdump. May look into this for 1.9.

@rsc rsc changed the title proposal: cmd/objdump: print Go code alongside assembly cmd/objdump: print Go code alongside assembly Jan 5, 2017
@gopherbot
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CL https://golang.org/cl/37953 mentions this issue.

@rugginoso
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@ALTree I've added you for the code review since you looked at this issue.

@dr2chase
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dr2chase commented Mar 9, 2017

You might want to see how the output looks in combination with https://go-review.googlesource.com/c/36207/ . This is designed to reduce the amount of churn in line numbers from optimization (mostly from value movement in/out of registers) and might lead to somewhat more sensible output. Longer-term we ought to make use of Dwarf's support for "not a line number" but for now the unimportant instructions inherit line numbers from their predecessor.

@rugginoso
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@dr2chase for the binary I tested (the one generated from src/cmd/objdump/testdata/fmthello.go), the output is the same as without CL 36207 (pasting here both outputs in the case I miss something):

Without 36207:

TEXT main.main(SB) /home/rugginoso/Documents/src/go/src/cmd/objdump/testdata/fmthello.go
func main() {
			0x47c2a0	64488b0c25f8ffffff	FS MOVQ FS:0xfffffff8, CX
			0x47c2a9	483b6110		CMPQ 0x10(CX), SP
			0x47c2ad	7631			JBE 0x47c2e0
			0x47c2af	4883ec18		SUBQ $0x18, SP
			0x47c2b3	48896c2410		MOVQ BP, 0x10(SP)
			0x47c2b8	488d6c2410		LEAQ 0x10(SP), BP
	Println("hello, world")
			0x47c2bd	488d0513b20200		LEAQ 0x2b213(IP), AX
			0x47c2c4	48890424		MOVQ AX, 0(SP)
			0x47c2c8	48c74424080c000000	MOVQ $0xc, 0x8(SP)
			0x47c2d1	e81a000000		CALL main.Println(SB)
}
			0x47c2d6	488b6c2410	MOVQ 0x10(SP), BP
			0x47c2db	4883c418	ADDQ $0x18, SP
			0x47c2df	c3		RET
func main() {
			0x47c2e0	e8cbf3fcff	CALL runtime.morestack_noctxt(SB)
			0x47c2e5	ebb9		JMP main.main(SB)

With 36207:

TEXT main.main(SB) /home/rugginoso/Documenti/src/go/src/cmd/objdump/testdata/fmthello.go
func main() {
			0x47c850	64488b0c25f8ffffff	FS MOVQ FS:0xfffffff8, CX	
			0x47c859	483b6110		CMPQ 0x10(CX), SP		
			0x47c85d	7631			JBE 0x47c890			
			0x47c85f	4883ec18		SUBQ $0x18, SP			
			0x47c863	48896c2410		MOVQ BP, 0x10(SP)		
			0x47c868	488d6c2410		LEAQ 0x10(SP), BP		
	Println("hello, world")
			0x47c86d	488d0563ac0200		LEAQ 0x2ac63(IP), AX	
			0x47c874	48890424		MOVQ AX, 0(SP)		
			0x47c878	48c74424080c000000	MOVQ $0xc, 0x8(SP)	
			0x47c881	e81a000000		CALL main.Println(SB)	
}
			0x47c886	488b6c2410	MOVQ 0x10(SP), BP	
			0x47c88b	4883c418	ADDQ $0x18, SP		
			0x47c88f	c3		RET			
func main() {
			0x47c890	e82bf1fcff	CALL runtime.morestack_noctxt(SB)	
			0x47c895	ebb9		JMP main.main(SB)

This example is probably too simplistic.

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