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cmd/cgo: structure used when calling Go function from C is not properly packed on 32-bit Windows with recent GCC #6833

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gopherbot opened this issue Nov 25, 2013 · 12 comments
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cmd/cgo: structure used when calling Go function from C is not properly packed on 32-bit Windows with recent GCC #6833

gopherbot opened this issue Nov 25, 2013 · 12 comments
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@gopherbot
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by 0x6a67:

What steps will reproduce the problem?
Run simple test program  https://gist.github.com/anonymous/7644960

What is the expected output?
expected : 4000300020001007
got      : 4000300020001007

What do you see instead?
expected : 4000300020001007
got      :   12feec20001000

Which compiler are you using (5g, 6g, 8g, gccgo)?
8g

Which operating system are you using?
Windows XP 32-bit

Which version are you using?  (run 'go version')
go version go1.2rc5 windows/386
gcc (rev0, Built by MinGW-W64 project) 4.8.2

Please provide any additional information below.
Revision ae83f4b0aa29 fixed packing of structure used when calling C function from Go
@alexbrainman
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Comment 1:

I don't see your problem here on windows/386:
C:\go\path\src\issue6833>go build && issue6833.exe
expected : 4000300020001007
got      : 4000300020001007
C:\go\path\src\issue6833>gcc --version
gcc (tdm-1) 4.5.2
Copyright (C) 2010 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Alex

@gopherbot
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Comment 2 by 0x6a67:

Sorry for too concise report.
Problem shows up starting from gcc 4.7, see issue #5603.

@gopherbot
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Comment 3 by salvor.public:

I can reproduce this bug using the following:
OS:  Windows 8 64-bit on Intel Core i7
Go:  go1.2rc5 windows/386
gcc: gcc (tdm-2) 4.8.1
The output I get on windows/386 is:
expected : 4000300020001007
got      :    a000920001000
I installed TDM-GCC (32-bit) from the individual .lzma files at
http://tdm-gcc.tdragon.net/download
I'll help test patches if they become available.

@rsc
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rsc commented Nov 27, 2013

Comment 4:

Labels changed: added go1.3maybe.

@alexbrainman
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Comment 5:

Yes it is broken with gcc-4.8.1:
C:\go\path\src\issue6833>go build && issue6833.exe
expected : 4000300020001007
got      :   12feec20001000
C:\go\path\src\issue6833>gcc --version
gcc (tdm-2) 4.8.1
Copyright (C) 2013 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
But I have no idea how to fix it.
Alex

@gopherbot
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Comment 6 by 0x6a67:

Applying fix from revision ae83f4b0aa29 to function writeExports in src/cmd/cgo/out.go
fixes issue for me (Windows 32-bit, gcc 4.8.2).
Note that in code and comments in fuction writeExports __attribute__((packed)) is used.

@alexbrainman
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Comment 7:

0x6a67, like https://golang.org/cl/35790045 ?
Alex

Status changed to Started.

@gopherbot
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Comment 8 by 0x6a67:

Patch looks good.
On 32-bit Windows XP with gcc 4.8.2 :
- ALL TESTS PASSED when building from patched source
- expected : 4000300020001007
  got      : 4000300020001007
  from original test case
Thank you.

@alexbrainman
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Comment 9:

Thank you. I will submit once source tree is opened for changes.
Alex

@rsc
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rsc commented Dec 4, 2013

Comment 10:

Labels changed: added release-none, removed go1.3maybe.

@rsc
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rsc commented Dec 4, 2013

Comment 11:

Labels changed: added repo-main.

@alexbrainman
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Comment 12:

This issue was closed by revision 6795687.

Status changed to Fixed.

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@rsc @gopherbot @alexbrainman