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Date: Tue, 7 Jul 2015 20:27:46 +0200
From: Alex <>
Subject: Re: [PATCH v9] Build process uses script to add CFI directives
 to x86 asm

On Tue, Jul 7, 2015 at 8:15 PM, Rich Felker <> wrote:
> On Tue, Jul 07, 2015 at 06:40:18PM +0200, Alex wrote:
>> On Tue, Jul 7, 2015 at 3:21 PM, Rich Felker <> wrote:
>> > On Tue, Jul 07, 2015 at 07:45:34AM +0200, Alex wrote:
>> >> On Tue, Jul 7, 2015 at 5:39 AM, Rich Felker <> 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:
>> 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?
> 1. Command line is "gcc -g canbt.c". With -static, syscall_cp gets
> optimized out to a normal syscall unless there's a reference to
> pthread_cancel, and the backtrace fully works. It did not work prior
> to your patch. But with dynamic linking, or with pthread_cancel.o
> pulled in when static linking, the backtrace produces (dynamic):

OK, I presume you are testing on a 32-bit OS. Is it Alpine Linux?

> 2. I suspect a dynamic-linked binary without the corresponding
> is not useful. Do you want the static-linked binary with a reference
> to pthread_cancel added?

I want to see the DWARF data, and in this case it should be in, not in canbt. But let me test under conditions more similar
to yours first.

Thanks, AD

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