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CarlRBauer / sawbuck

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Only first function in an assembly file was shown in the profiling result #66

Closed GoogleCodeExporter closed 9 years ago

GoogleCodeExporter commented 9 years ago 
What steps will reproduce the problem?
1.Build chrome on Windows (visual studio 2010);
2.Instrument chrome.dll, and then run chrome
3.Open chrome.callgrind using qcachegrind.exe.

What is the expected output? What do you see instead?
Expected output: show all functions in assembly file.
We use assembler YASM, and only the first function in an assembly file is 
shown. For example,  in 
C:\cygwin\home\yunqingwang\src\third_party\libvpx\source\libvpx\vp8\encoder\x86\
dct_sse2.asm
vp8_short_fdct4x4_sse2 was shown, but vp8_short_fdct8x4_sse2 wasn't shown.

What version of the product are you using? On what operating system?
SyzyProf 0.2.10.0 on Windows 7.

Please provide any additional information below.
For easy reproducing the issue, I attached a small test project. Please refer 
to the Readme.txt for more information.

Original issue reported on code.google.com by yunqingw...@google.com on 15 Dec 2012 at 12:48

Attachments:

GoogleCodeExporter commented 9 years ago 
What's going on here is that yasm generates a single "COMDAT" for the contents 
of each .ASM file. The instrumenter is conservative in what it will instrument, 
in that it'll only instrument pointers to the start of a "COMDAT" (which 
appears to the instrumenter as a "section contribution" in symbol information).
By adding a unique section/segment directive before each function declaration, 
e.g. 

section .text$2

;void vp8_short_fdct4x4_sse2(short *input, short *output, int pitch)
global sym(vp8_short_fdct4x4_sse2) PRIVATE
sym(vp8_short_fdct4x4_sse2):

Yasm will implicitly generate separate "COMDATs", as each function is assigned 
a separate segment.
Maybe this could be folded into a new macro, "function(x)" which could 
concatenate e.g. __LINE__ into a SECTION directive?

I see there's a feature request filed against yasm to add comdats 
[http://tortall.lighthouseapp.com/projects/78676/tickets/210-support-comdat-sect
ionsymbol-for-windowscoff], but it's been deferred several times.

It's not a bad idea to deposit each function in a separate COMDAT in any case, 
as otherwise the linker will bring in all the functions in a given .OBJ file 
(and the transitive closure of their dependencies) if even only one of them is 
referenced.

Alternatively we could make the instrumenter less conservative, although we 
know there are compiler support functions in the CRT that fall into the same 
general category of trouble, and so we'd have to find a way to back off on 
those functions somehow.

Original comment by siggi@chromium.org on 9 Jan 2013 at 8:54

GoogleCodeExporter commented 9 years ago 
Adding "SEGMENT .text$<unique_identifier>" in asm file did solve the problem. 
Thanks!

Original comment by yunqingw...@google.com on 10 Jan 2013 at 2:35

GoogleCodeExporter commented 9 years ago 
This issue is either invalid or it concern Chrome, if so please fill a bug at 
crbug.com

Original comment by sebmarch...@google.com on 26 Mar 2014 at 2:43