Re: [Qemu-devel] Problems with QEMU sdcard while using glib 2.33.8

[Stefan Hajnoczi <stefanha@gmail.com>]

On Thu, Sep 19, 2013 at 8:36 AM, Taimoor Mirza <taimoor.mrza@gmail.com> wrote:

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> O1 disassembly is at http://pastebin.com/yxWAmmmf
>
> O2 disassembly is at http://pastebin.com/v0uqHuYY

I diffed them.  The differences look reasonable, nothing obviously broken:
 * The broken -O2 version inlines qemu_coroutine_switch() into
coroutine_trampoline().
 * The broken -O2 version changes the ordering of basic blocks and
switches a few instructions for shorter/cheaper equivalents.

Taimoor: Can you try "make check" with the -O2 version?  In
particular, the test-coroutine tests may fail and that could help us
figure out which operation is broken.

Paolo: CCed you in case you want to diff the working -O1 against the
broken -O2 disassembly.  Perhaps Taimoor's gcc 4.6.2 -O2 subtly breaks
around the Windows Fiber API calls.

> On Wed, Sep 18, 2013 at 7:10 PM, Stefan Hajnoczi <stefanha@gmail.com> wrote:
>> On Thu, Sep 05, 2013 at 04:02:43PM +0500, Taimoor Mirza wrote:
>>> I am using released 1.5.0 version from http://wiki.qemu.org/Download.
>>> I think it should be same as commit ID
>>> "295d81c62414a63c625fa2e78175573d4b3f5ba4"
>>>
>>> I have observed some interesting behavior. This problem does not come
>>> if I use MinGW with GCC version 4.7.2. I was originally using 4.6.2. I
>>> spent some time looking at what can cause this problem and found out
>>> an interesting thing. If I change optimization flag from O2 to O1
>>> while building coroutine-win32 then it works fine even with 4.6.2.
>>> For this I first built QEMU binary with default O2 flag, remove
>>> coroutine-win32.o, changed CFLAG in makefile to O1 and rerun make.
>>> Generated binary works fine without any problem.
>>
>> Can you pastebin the output of "objdump -dr coroutine-win32.o" for both
>> -O2 and -O1?
>>
>> Let's diff them and figure out why it breaks with -O2.
>>
>> Stefan