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Re: RFC: Turn on -fomit-frame-pointer and -fasynchronous-unwind-tables for Linux/i386


On Thu, Jul 15, 2010 at 11:16 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Thu, Jul 15, 2010 at 11:08 AM, Chris Lattner <clattner@apple.com> wrote:
>>
>> On Jul 15, 2010, at 10:42 AM, H.J. Lu wrote:
>>
>>> Hi,
>>>
>>> This patch turns on -fomit-frame-pointer and -fasynchronous-unwind-tables
>>> for Linux/i386. ?Tested on Linux/ia32 and Linux/x86-64. ?I am also
>>> enclosing a spreadsheet of comparison of shared library segment sizes
>>> in gcc. ?Segment size differences range from -1% to 30%. The smaller
>>> the DSO size is, the bigger its size increases. Overall, the size
>>> difference is close to 0%. This comparison may not be typical since
>>> C++ and Java libraries have .eh_frame sections anyway. ?Any comments?
>>
>> Does glibc backtrace() look at eh_frame on i386? ?I suspect that most unwinders don't. ?This is a borderline ABI change.
>>
>
> It does:
>
> http://sourceware.org/git/?p=glibc.git;a=blob_plain;f=sysdeps/i386/backtrace.c;hb=HEAD
>

I updated the spread sheet with glibc 12.0 DSO sizes
I think -fomit-frame-pointer and -fasynchronous-unwind-tables
will increase size of DSO written in C by about 10%.


-- 
H.J.

Attachment: gcc frame pointer.xlsx
Description: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet


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