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Date: Tue, 7 Jul 2015 18:40:18 +0200
From: Alex <alexinbeijing@...il.com>
To: musl@...ts.openwall.com
Subject: Re: [PATCH v9] Build process uses script to add CFI directives
to x86 asm
On Tue, Jul 7, 2015 at 3:21 PM, Rich Felker <dalias@...c.org> wrote:
> On Tue, Jul 07, 2015 at 07:45:34AM +0200, Alex wrote:
>> On Tue, Jul 7, 2015 at 5:39 AM, Rich Felker <dalias@...c.org> wrote:
>> > On Tue, Jun 23, 2015 at 09:18:08PM +0200, Alex Dowad wrote:
>> >> Dear musl devs,
>> >>
>> >> ../configure now checks CFLAGS as well as CFLAGS_AUTO to see if generation of debug
>> >> info was requested.
>> >>
>> >> The idea of removing duplication from the Makefile using a new AS_CMD variable has
>> >> come up several times, but this will not work because the arguments need to be
>> >> inserted in different places. I have tried using a Makefile 'define' instead.
>> >> Please see whether you like the way this code reads or not.
>> >>
>> >> Subarch asm files are treated the same as other asm files. Please note that
>> >> since I don't own the hardware, I can't test whether these Makefile rules work or not.
>> >
>> > I'm trying to test this and get it merged, but I'm not having any luck
>> > getting gdb to backtrace when I interrupt a syscall with ^C. I've
>> > tried pause() and syscall(SYS_pause) (cancellable and non-cancellable)
>> > and the patch doesn't seem to help at all for the former, and only
>> > helps mildly for the latter. Have you had better results than I did?
>>
>> I tested a different set of library calls, with my own test programs.
>> Can you please send a copy of the test program you are using, and I
>> will debug? Thanks, AD
>
> Here it is. Compile with -g -O0 to make a more interesting backtrace
> (if it works).
Thanks for the test program. I compiled it with:
./tools/musl-gcc -Xlinker -melf_i386 -m32 -o canbt canbt.c
(That -Xlinker junk is because I am compiling to 32-bit code on a
64-bit machine.)
And then:
gdb ./canbt
Set a breakpoint on pause(), single-stepped all the way into the
innards of musl, and I was able to get a nice stack trace at each
stop. Sample of what it looks like at one randomly chosen point:
https://dl.dropboxusercontent.com/u/106217735/musl-debugging-pause.png
Could you please 1) tell me the command-line invocation you are using
to compile the test program and 2) send me a binary, so I can extract
the DWARF data from it and see what it looks like?
Thanks, AD
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