[maemo-developers] Help debugging segfaults

[From: Simon Pickering]

Hello everyone,

I don't have much experience debugging segfaults and would appreciate 
any pointers. I've compiled giac/xcas for the N800, but get a segfault 
when I try to run it (icas is the command line version).

The gdb output is as follows:

-------------------------------------------------------------------------------
Nokia-N800-51:/home/user# gdb ./icas
GNU gdb 6.4
Copyright 2005 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "arm-linux-gnueabi"...Using host 
libthread_db library "/lib/libthread_db.so.1".

(gdb) r
Starting program: /home/user/icas

Program received signal SIGSEGV, Segmentation fault.
0x41851380 in std::string::compare () from /usr/lib/libstdc++.so.6
(gdb) bt
#0  0x41851380 in std::string::compare () from /usr/lib/libstdc++.so.6
#1  0x0005fa28 in std::operator< <char, std::char_traits<char>, 
std::allocator<char> > (__lhs=@0x10, __rhs=@0xbe9d5538) at 
basic_string.h:2149
#2  0x401e1260 in std::less<std::string>::operator() () from 
/usr/lib/libgiac.so.0
#3  0x401e17fc in std::_Rb_tree<std::string, std::pair<std::string 
const, giac::gen>, std::_Select1st<std::pair<std::string const, 
giac::gen> >, std::less<std::string>, 
std::allocator<std::pair<std::string const, giac::gen> > 
 >::insert_unique () from /usr/lib/libgiac.so.0
#4  0x401e1378 in std::map<std::string, giac::gen, 
std::less<std::string>, std::allocator<std::pair<std::string const, 
giac::gen> > >::insert ()
    from /usr/lib/libgiac.so.0
#5  0x401e0cc4 in std::map<std::string, giac::gen, 
std::less<std::string>, std::allocator<std::pair<std::string const, 
giac::gen> > >::operator[] ()
    from /usr/lib/libgiac.so.0
#6  0x4053a6f4 in giac::lexer_functions_register () from /usr/lib/libgiac.so.0
#7  0x404b1354 in giac::unary_function_ptr::unary_function_ptr () from 
/usr/lib/libgiac.so.0
#8  0x40135a7c in giac::_resultant () from /usr/lib/libgiac.so.0
#9  0x40136e88 in giac::_resultant () from /usr/lib/libgiac.so.0
#10 0x4100b28c in _dl_rtld_di_serinfo () from /lib/ld-linux.so.3
#11 0x00026980 in ?? ()
#12 0x00026980 in ?? ()
Previous frame identical to this frame (corrupt stack?)
(gdb) q
The program is running.  Exit anyway? (y or n) y
-------------------------------------------------------------------------------

The tail end of the strace output is as follows:

-------------------------------------------------------------------------------
open("/usr/lib/libXdmcp.so.6", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0\344\216"..., 
512) = 512
fstat64(3, {st_mode=S_IFREG|0644, st_size=17592186044416, ...}) = 0
mmap2(0x413e8000, 47256, PROT_READ|PROT_EXEC, 
MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x413e8000
mprotect(0x413eb000, 34968, PROT_NONE)  = 0
mmap2(0x413f2000, 8192, PROT_READ|PROT_WRITE, 
MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x2) = 0x413f2000
close(3)                                = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 
0) = 0x4071b000
mprotect(0x4112b000, 8192, PROT_READ)   = 0
mprotect(0x4132c000, 4096, PROT_READ)   = 0
mprotect(0x411f9000, 4096, PROT_READ)   = 0
mprotect(0x41215000, 4096, PROT_READ)   = 0
mprotect(0x40008000, 6991872, PROT_READ|PROT_WRITE) = 0
mprotect(0x40008000, 6991872, PROT_READ|PROT_EXEC) = 0
mprotect(0x4101e000, 4096, PROT_READ)   = 0
munmap(0x40000000, 24576)               = 0
getrlimit(RLIMIT_STACK, {rlim_cur=8192*1024, rlim_max=RLIM_INFINITY}) = 0
setrlimit(RLIMIT_STACK, {rlim_cur=8192*1024, rlim_max=RLIM_INFINITY}) = 0
getpid()                                = 3049
rt_sigaction(SIGRTMIN, {0x41207d08, [RT_6 RT_9 RT_10 RT_11 RT_12 RT_13 
RT_16 RT_17 RT_21 RT_22 RT_23 RT_31], 0x4000000 /* SA_??? */}, NULL, 8) 
= 0
rt_sigaction(SIGRT_1, {0x41207dd4, [RTMIN RT_6 RT_9 RT_10 RT_11 RT_12 
RT_13 RT_16 RT_17 RT_21 RT_22 RT_23 RT_31], 0x4000000 /* SA_??? */}, 
NULL, 8) = 0
rt_sigaction(SIGRT_2, {0x41207dd4, [RTMIN RT_6 RT_9 RT_10 RT_11 RT_12 
RT_13 RT_16 RT_17 RT_21 RT_22 RT_23 RT_31], 0x4000000 /* SA_??? */}, 
NULL, 8) = 0
rt_sigprocmask(SIG_BLOCK, [RTMIN], NULL, 8) = 0
rt_sigprocmask(SIG_UNBLOCK, [], NULL, 8) = 0
_sysctl({(nil), -1098230264, 0x41216240, 0xbe8a560c, 0x4121623c, 
1092706304}0xbe8a5388, 512, (nil), 0}) = 0
brk(0)                                  = 0x18a000
brk(0x1ab000)                           = 0x1ab000
--- SIGSEGV (Segmentation fault) @ 0 (0) ---
+++ killed by SIGSEGV +++
Process 3049 detached
-------------------------------------------------------------------------------

If anyone has any bright ideas (As to what's wrong, or how to find out) 
I'd be glad to hear them.

Many thanks,


Simon