https://sourceware.org/bugzilla/show_bug.cgi?id=21900
Bug ID: 21900
Summary: [MIPS] linking shared library with -z defs
--warn-unresolved-symbols emits null relocation
Product: binutils
Version: 2.29
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: ld
Assignee: unassigned at sourceware dot org
Reporter: james410 at cowgill dot org.uk
Target Milestone: ---
Hi,
On MIPS, using "-z defs" and "--warn-unresolved-symbols" while building a
shared library with undefined symbols seems to cause all the relocations which
use those symbols to be filled with null values. The executables then crash
when executed because they load a garbage address into t9 and jump to it. Here
is an example:
> $ cat undef.c
> int parent(void);
>
> int child(void)
> {
> return parent();
> }
>
> $ mips-linux-gnu-gcc -c -fPIC -O2 undef.c
> $ ../build-mips/ld/ld-new -EB -shared -z defs --warn-unresolved-symbols
> undef.o -o libundef.so
> undef.o: In function `child':
> undef.c:(.text+0xc): warning: undefined reference to `parent'
> undef.c:(.text+0x10): warning: undefined reference to `parent'
> $ mips-linux-gnu-objdump -dr libundef.so
>
> libundef.so: file format elf32-tradbigmips
>
> Disassembly of section .text:
>
> 00000300 <child>:
> 300: 3c1c0002 lui gp,0x2
> 304: 279c8030 addiu gp,gp,-32720
> 308: 0399e021 addu gp,gp,t9
> 30c: 8f990000 lw t9,0(gp)
> 310: 03200008 jr t9
> 314: 00000000 nop
> ...
Note the line:
> lw t9,0(gp)
I would have expected a different offset than 0. If you remove the "-z defs"
option to ld, a valid library is generated.
This was observed while trying to debug a long standing issue where
gnome-settings-daemon would immediately SIGBUS on startup. I have not
personally tested old versions of binutils, but this bug suggests that it was
broken on 2011 and a similar bug affects (or affected) ia64 as well:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=620874#40
Thanks,
James
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