Re: Solution sought to GCC 4.1.1 backtrace problem

[Andrew Haley <aph-gcc at littlepinkcloud dot COM>]

Blair Barnett writes:
 > Hi Andrew,
 > 
 > So our experiment with the 4.1.1 EABI compiler along with your patch provided no new results.
 > 
 > I applied your patch and recompiled arm-linux-gcc and recompiled our little test program. I copied the program to our arm device and ran it, obtaining the following output:
 > 
 > arm-linux-gcc -o fault-unwind fault.c
 > 
 >  ./fault-unwind
 > in routine1 at 0x00008874
 > in routine2 at 0x0000882c
 > in routine3 at 0x000087e4
 > in routine4 at 0x00008794
 > in catch_segfault
 > Obtained 1 stack frames.
 > /lib/ld-linux.so.2 [0x40012f84]
 > Segmentation fault

That's what I predicted, right?

 > 
 > 
 > If we run the 4.1.2 compiler included with ubuntu on our little test program, we get the following results:
 > 
 > bbarnett@kitt:~$ gcc -v
 > Using built-in specs.
 > Target: i486-linux-gnu
 > Configured with: ../src/configure -v --enable-languages=c,c++,fortran,objc,obj-c++,treelang --prefix=/usr --enable-shared --with-system-zlib --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --enable-nls --program-suffix=-4.1 --enable-__cxa_atexit --enable-clocale=gnu --enable-libstdcxx-debug --enable-mpfr --enable-checking=release i486-linux-gnu
 > Thread model: posix
 > gcc version 4.1.2 (Ubuntu 4.1.2-0ubuntu4)
 > bbarnett@kitt:~$ gcc -o fault fault.c
 > bbarnett@kitt:~$ ./fault
 > in routine1 at 0x080486de
 > in routine2 at 0x080486ae
 > in routine3 at 0x0804867e
 > in routine4 at 0x0804864a
 > in catch_segfault
 > Obtained 8 stack frames.
 > ./fault [0x8048547]
 > [0xffffe420]
 > ./fault [0x80486ac]
 > ./fault [0x80486dc]
 > ./fault [0x804870c]
 > ./fault [0x8048730]
 > /lib/tls/i686/cmov/libc.so.6(__libc_start_main+0xdc) [0xb7e5febc]
 > ./fault [0x8048491]
 > Segmentation fault (core dumped)
 > 
 > So glibc backtrace() appears to work in an EABI environment, just not an ARM EABI environment.

Sure, because ARM doesn't have fallback_frame_state_for, like I said.
x86 does.

Remember what I advised you to do:

--------------------------------------------------------------------
The SIGCONTEXT ctx that's passed to your segfault handler contains the
registers at the point the segfault occurred, and you can unwind
starting from there.

Don't do this:

   void *fp = __builtin_frame_address (0);

Instead, pull fp and sp out of the SIGCONTEXT ctx.

--------------------------------------------------------------------


Andrew.