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[Bug libc/2683] dladdr() returns wrong symbol names in rare cases
- From: "satoru at 0xcc dot net" <sourceware-bugzilla at sourceware dot org>
- To: glibc-bugs at sources dot redhat dot com
- Date: 28 May 2006 05:04:12 -0000
- Subject: [Bug libc/2683] dladdr() returns wrong symbol names in rare cases
- References: <20060522145631.2683.satoru@0xcc.net>
- Reply-to: sourceware-bugzilla at sourceware dot org
------- Additional Comments From satoru at 0xcc dot net 2006-05-28 05:04 -------
(In reply to comment #1)
> Correct patch, I applied it to CVS.
Thank you for fixing the bug.
I just realized that completly skipping undefined references
could be a problem. Consider the following code.
#include <stdio.h>
int main() {
printf("%p\n", &printf);
return 0;
}
If I compile it without -fPIC on my machine (Debian GNU/Linux sarge on a x86_32
machine),
&printf points to a memory address in PLT.
% gcc test.c
% ./a.out
0x8048288
% readelf -S a.out |grep " \.plt"
[11] .plt PROGBITS 08048270 000270 000030 04 AX 0 0 4
The binary contains the undefined symbols for printf both in
.dysym and .symtab sections and the values of the undefined symbols
correspond to the memory address in PLT (0x8048288).
% readelf --symbols a.out |grep printf
2: 08048288 57 FUNC GLOBAL DEFAULT UND printf@GLIBC_2.0 (2)
99: 08048288 57 FUNC GLOBAL DEFAULT UND printf@@GLIBC_2.0
Hence, to support dladdr(&printf, info) for non-pic binaries,
probably we need to allow the condition something like this as well.
(ELFW(ST_TYPE) (symtab->st_info) == STT_FUNC
&& symtab->st_shndx == SHN_UNDEF
&& match->l_addr + symtab->st_value == addr)
On the other hand, if I compile the same code with -fPIC,
&printf points to the printf definition in the map of glibc.
There is no problem in this case for doing dladdr(&printf, info).
% gcc -fPIC test.c
% ./a.out
0x4006e8e0
% ldd a.out
libc.so.6 => /lib/libc.so.6 (0x4001f000)
/lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000)
% readelf --symbols /lib/libc.so.6|grep " printf"
157: 0004f8e0 57 FUNC GLOBAL DEFAULT 11 printf@@GLIBC_2.0
% python
>>> "%x" % (0x4001f000 + 0x0004f8e0)
'4006e8e0'
--
What |Removed |Added
----------------------------------------------------------------------------
Status|RESOLVED |REOPENED
Resolution|FIXED |
http://sourceware.org/bugzilla/show_bug.cgi?id=2683
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