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x/arch/x86/x86asm: Mem.Disp is positive for negative displacements #8000

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josharian opened this issue May 15, 2014 · 4 comments
Open

x/arch/x86/x86asm: Mem.Disp is positive for negative displacements #8000

josharian opened this issue May 15, 2014 · 4 comments
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@josharian
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@josharian josharian commented May 15, 2014

The instruction 48 8b 0c 25 c0 5c 07 80 is disassembled as MOVQ 0x80075cc0, CX. It
should be disassembled as MOVQ 0xffffffff80075cc0, CX. Addresses are signed, and should
be sign-extended. See the discussion in issue #7980 for details.

To reproduce, run 'go tool objdump addr31 0x2000 0x2012'. addr31 is attached. It was
created by stripping a binary built from the code in issue #7980.

Attachments:

  1. addr31.gz (153196 bytes)
@rsc rsc added this to the Unplanned milestone Apr 10, 2015
@minux minux changed the title cmd/objdump: incorrect disassembly of MOV instruction with address > 2^31-1 x/arch/x86/x86asm: Mem.Disp is positive for negative displacements Jan 15, 2017
@josharian
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@josharian josharian commented Jan 15, 2017

(Migrating comment from #18666)

I worked on a CL for this ages ago: https://codereview.appspot.com/100480046/. It may serve as a useful starting point for anyone fixing this.

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@minux
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@minux minux commented Jan 16, 2017

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@josharian
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@josharian josharian commented Jan 16, 2017

My understanding is far more limited than yours. But I think you are correct.

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@josharian
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@josharian josharian commented Jan 16, 2017

...that is, that the changes in those cases should be reverted.

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3 participants