[Bug libc/17176] New: backtrace() not working on ARMv7a

[Bug libc/17176] New: backtrace() not working on ARMv7a

[prafulla.fin at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=17176

            Bug ID: 17176
           Summary: backtrace() not working on ARMv7a
           Product: glibc
           Version: 2.18
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: prafulla.fin at gmail dot com
                CC: drepper.fsp at gmail dot com

Created attachment 7716
  --> https://sourceware.org/bugzilla/attachment.cgi?id=7716&action=edit
c file to simulate the error.

Hi,

I am trying to generate a call stack trace using backtrace() API which is part
of libbacktrace. The idea is to catch a SIGSEGV signal and call backtrace() to
print all the address values and compare the obtained addresses from objdump -D
of executable. Attached is a simplified version of the application. Following
is the output seen on ARMv7a platform with buildroot cross-toolchain (gcc-
4.8.2, binutis-2.18.1).

To compile the application:
${CROSS_COMPILE}gcc -o crash_test -O0 -funwind-tables -rdynamic crash_test.c

ARMv7a# ./crash_test
Trying to access NULL pointer!
SIGSEGV Handler!
Got Backtrace Size=2
0x00008724
0x000087c4
ARMv7a#

The above function call trace is only that of the signal hander
(print_back_trace, sigsegv_handler) and does not show the entire call stack for
the function where program crashed (print_back_trace, sigsegv_handler, func2,
main).

On x86 host same program shows a deeper function call trace right up to the
main function and even beyond:
x86-RHEL5-host$./crash_test
Trying to access NULL pointer!
SIGSEGV Handler!
Got Backtrace Size=7
0x00400939
0x004009ab
0x30930302f0
0x004009d3
0x00400a7b
0x309301d994
0x00400889
x86-RHEL5-host$

Can someone please comment on what is going wrong. Any special flags that need
to be used while compiling/linking the program.

http://lists.uclibc.org/pipermail/uclibc/2013-September/047932.html

Similar issue in uclibc was solved by creating a patch to uclibc files, can
some one let me know if there is any existing patch is available for glibc
similar to this?, if not can anyone help me in providing the similar patch for
glibc.

Please let me know if i can provide any info.

/Thanks
Prafulla

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[Bug libc/17176] backtrace() not working on ARMv7a

[joseph at codesourcery dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=17176

--- Comment #1 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
First, you should make sure that the debug/tst-backtrace* tests pass when 
you run the glibc testsuite.  Then, investigate how your test differs from 
those tests.

Note that ARM EABI unwind info (as generated by GCC) does not fully 
support asynchronous unwinding even if you use 
-fasynchronous-unwind-tables.

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[Bug libc/17176] backtrace() not working on ARMv7a

[prafulla.fin at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=17176

--- Comment #2 from prafulla chandra kota <prafulla.fin at gmail dot com> ---
Hi Joseph/All,

Thanks for your inputs, I will verify the tests you suggested.

Below links shows that patch is added for same issue in ulibc. I was wondering
if there is a similar patch available for glibc as well.

http://lists.uclibc.org/pipermail/uclibc/2013-September/047932.html

We observed that stack trace is working fine after the patch in ulibc, We
needed the same for glibc as well.

Thanks,
Prafulla

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[Bug libc/17176] backtrace() not working on ARMv7a

[prafulla.fin at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=17176

--- Comment #3 from prafulla chandra kota <prafulla.fin at gmail dot com> ---
Hi All,

Appreciate if somebody could provide the fix for backtrace for below issue as
an example

void func1() {
  int    val;
  char buf[256];
  val = 100;
  printf("\nTrying to construct invalid buffer!\n");
  snprintf(buf, sizeof (buf), "%s", val);
  printf("The content of buf: %s\n", buf);

}

For other issues like NULL pointer access or invalid memory access, backtrace
is working fine in glibc but not for above type of issues.

For above issue uclibc forum has given fix in below link
http://lists.uclibc.org/pipermail/uclibc/2013-September/047932.html

I am looking for similar fix info or patch, so that i can make changes if
someone points out relevant changes.

Thanks,
Prafulla Kota.

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[Bug libc/17176] backtrace() not working on ARMv7a

[joseph at codesourcery dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=17176

--- Comment #4 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
You are free to configure your compiler to default to 
-fasynchronous-unwind-tables if you want, or to build glibc with that 
option, but I don't think it's an appropriate default for glibc; it should 
be used in glibc only for specific files where asynchronous cancellation 
may occur.

When you make invalid use of glibc - passing arguments to functions that 
result in undefined behavior - there is no guarantee that the stack is in 
an unwindable state when the segfault occurs (return addresses may have 
been overwritten as a result of the invalid arguments, for example).

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