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cmd/objdump: use symbolic names for globals #20650

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randall77 opened this issue Jun 12, 2017 · 5 comments
Closed

cmd/objdump: use symbolic names for globals #20650

randall77 opened this issue Jun 12, 2017 · 5 comments
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@randall77
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randall77 commented Jun 12, 2017 •
edited 

package main

var g int

func main() {
	println(g)
}

> go build tmp.go
> go tool objdump -s main.main tmp

TEXT main.main(SB) /usr/local/google/home/khr/go/tmp.go
	tmp.go:5	0x44e590	64488b0c25f8ffffff	FS MOVQ FS:0xfffffff8, CX		
	tmp.go:5	0x44e599	483b6110		CMPQ 0x10(CX), SP			
	tmp.go:5	0x44e59d	7637			JBE 0x44e5d6				
	tmp.go:5	0x44e59f	4883ec10		SUBQ $0x10, SP				
	tmp.go:5	0x44e5a3	48896c2408		MOVQ BP, 0x8(SP)			
	tmp.go:5	0x44e5a8	488d6c2408		LEAQ 0x8(SP), BP			
	tmp.go:6	0x44e5ad	e86e55fdff		CALL runtime.printlock(SB)		
	tmp.go:6	0x44e5b2	488b056f9a0600		MOVQ 0x69a6f(IP), AX			
	tmp.go:6	0x44e5b9	48890424		MOVQ AX, 0(SP)				
	tmp.go:6	0x44e5bd	e81e5dfdff		CALL runtime.printint(SB)		
	tmp.go:6	0x44e5c2	e84958fdff		CALL runtime.printnl(SB)		
	tmp.go:6	0x44e5c7	e8e455fdff		CALL runtime.printunlock(SB)		
	tmp.go:7	0x44e5cc	488b6c2408		MOVQ 0x8(SP), BP			
	tmp.go:7	0x44e5d1	4883c410		ADDQ $0x10, SP				
	tmp.go:7	0x44e5d5	c3			RET					
	tmp.go:5	0x44e5d6	e81584ffff		CALL runtime.morestack_noctxt(SB)	
	tmp.go:5	0x44e5db	ebb3			JMP main.main(SB)

Note the MOVQ 0x69a6f(IP), AX instruction. It would be nice if this instead read MOVQ main.g(IP), AX or something.
We do the address->symbol mapping for CALLs, so I suspect we just need to enable that for IP-relative addressing also.
@randall77 randall77 added this to the Go1.10 milestone Jun 12, 2017
@robbert229
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I can take a look at this. @randall77

So far from my understanding of objdump the changes for this feature would need to occur in each of the assembly packages used by disasm.go in the cmd/internal/objfile package

"golang.org/x/arch/arm/armasm"
"golang.org/x/arch/ppc64/ppc64asm"
"golang.org/x/arch/x86/x86asm"

I think the changes would be to the decode function in each of the previously stated packages, is this correct?

@randall77
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Those are the right packages. I think the code might need to be added to plan9x.go:plan9Arg (at least on x86).

@ccbrown
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ccbrown commented Sep 11, 2017

So this is pretty easy to do. In fact, I have a patch that I believe does the job. And I've tested it and it works just fine as far as I can tell:

package main

var g = "foo"

func main() {
	println(g)
}
chris@mbp:~/repos/golang/go% ./bin/go tool objdump -s main.main tmp
TEXT main.main(SB) /Users/chris/repos/golang/go/tmp.go
  tmp.go:5		0x104f2c0		65488b0c25a0080000	MOVQ GS:0x8a0, CX			
  tmp.go:5		0x104f2c9		483b6110		CMPQ 0x10(CX), SP			
  tmp.go:5		0x104f2cd		7643			JBE 0x104f312				
  tmp.go:5		0x104f2cf		4883ec18		SUBQ $0x18, SP				
  tmp.go:5		0x104f2d3		48896c2410		MOVQ BP, 0x10(SP)			
  tmp.go:5		0x104f2d8		488d6c2410		LEAQ 0x10(SP), BP			
  tmp.go:6		0x104f2dd		e87e3ffdff		CALL runtime.printlock(SB)		
  tmp.go:6		0x104f2e2		488b0547770500		MOVQ main.g(SB), AX			
  tmp.go:6		0x104f2e9		488b0d48770500		MOVQ main.g+8(SB), CX			
  tmp.go:6		0x104f2f0		48890424		MOVQ AX, 0(SP)				
  tmp.go:6		0x104f2f4		48894c2408		MOVQ CX, 0x8(SP)			
  tmp.go:6		0x104f2f9		e80249fdff		CALL runtime.printstring(SB)		
  tmp.go:6		0x104f2fe		e80d42fdff		CALL runtime.printnl(SB)		
  tmp.go:6		0x104f303		e8e83ffdff		CALL runtime.printunlock(SB)		
  tmp.go:7		0x104f308		488b6c2410		MOVQ 0x10(SP), BP			
  tmp.go:7		0x104f30d		4883c418		ADDQ $0x18, SP				
  tmp.go:7		0x104f311		c3			RET

chris@mbp:~/repos/golang/go% ./bin/go tool objdump -s main.main tmparm
TEXT main.main(SB) /Users/chris/repos/golang/go/tmp.go
  tmp.go:5		0x5ba00			e59a1008		MOVW 0x8(R10), R1		
  tmp.go:5		0x5ba04			e15d0001		CMP R1, R13			
  tmp.go:5		0x5ba08			9a00000b		B.LS 0x5ba3c			
  tmp.go:5		0x5ba0c			e52de00c		MOVW.W R14, -0xc(R13)		
  tmp.go:6		0x5ba10			ebff6154		BL runtime.printlock(SB)	
  tmp.go:6		0x5ba14			e59fb030		MOVW $main.g(SB), R11		
  tmp.go:6		0x5ba18			e59b0000		MOVW (R11), R0			
  tmp.go:6		0x5ba1c			e59fb02c		MOVW $main.g+4(SB), R11		
  tmp.go:6		0x5ba20			e59b1000		MOVW (R11), R1			
  tmp.go:6		0x5ba24			e58d0004		MOVW R0, 0x4(R13)		
  tmp.go:6		0x5ba28			e58d1008		MOVW R1, 0x8(R13)		
  tmp.go:6		0x5ba2c			ebff63a6		BL runtime.printstring(SB)	
  tmp.go:6		0x5ba30			ebff61ce		BL runtime.printnl(SB)		
  tmp.go:6		0x5ba34			ebff6168		BL runtime.printunlock(SB)	
  tmp.go:7		0x5ba38			e49df00c		RET #12

But what I just can't figure out is how the x/arch tests are supposed to be run. A lot of them are skipped because my environment isn't what's expected (e.g. "/Users/rsc/bin/objdump2" doesn't exist), and a lot of them fail with errors such as this:

ext_test.go:171: decode(0511223344556677885f5f5f5f5f5f5f) = "ADDL $0x44332211, AX", 5, want "ADDL $0x44332211,AX", 5

Of course, this is with a clean working directory. No source changes or anything.

Does anyone (@rsc?) know if there's an easy way I can actually get all of these running and passing?
I haven't been able to find any useful documentation here and I'd love to actually get my changes submitted. Thanks!

@rsc rsc modified the milestones: Go1.10, Go1.11 Nov 22, 2017
@gopherbot
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Change https://golang.org/cl/80843 mentions this issue: cmd/vendor/golang.org/x/arch: revendor at commit dda8112

gopherbot pushed a commit that referenced this issue Nov 29, 2017
@cherrymui
cmd/vendor/golang.org/x/arch: revendor at commit dda8112
905b1c9 
Updates #20650 (CL 45099 introduced the feature to x86).

Change-Id: If40cc9d87417a05281d8633f05cd91f6f434b136
Reviewed-on: https://go-review.googlesource.com/80843
Run-TryBot: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
@ianlancetaylor ianlancetaylor modified the milestones: Go1.11, Unplanned Jun 14, 2018
@randall77
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This looks like it has been fixed.

@golang golang locked and limited conversation to collaborators Dec 2, 2020
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