linker relocation of debug information

Daniel Jacobowitz drow@mvista.com
Fri Jan 23 19:08:00 GMT 2004


On Fri, Jan 23, 2004 at 02:06:00PM -0500, Kris Warkentin wrote:
> I've noticed with ld 2.12.1 that sometimes debug information isn't 
> relocated in shared libs.  Particularily, I'm seeing that the old 
> relocations still happen with i386 and mips but not with sh, arm or powerpc.
> 
> The problem that I'm having is that we're shipping gdb 5.2.1 which 
> doesn't seem to be able to deal with the unrelocated debug info when 
> stepping into shared libs although newer gdbs can.  Can anyone give me 
> any information about this?  Is debug info relocation deprecated?  Am I 
> completely misunderstanding what's going on here?

You could take a look at the other differences between the libraries,
namely, that relocation sections are emitted from the debug
information.  GDB 6.0 explicitly processes this information.

Personally, I think this is a dumb policy, and that relocating
.stab/.debug_info at link time is always appropriate for shared
libraries.  This has come up at least three times in the list archives
for the past two years.

For instance, this will have severe performance implications for GDB,
in that a current bottleneck that I plan to fix won't be fixable for
such libraries.

Note that GDB has to process the relocation data anyway in order to
load unlinked objects using add-symbol-file.

> 
> cheers,
> 
> Kris
> 
> ***OLD***
> int blah /* 0x17d8 */;
> unsigned int some_global /* 0x17dc */;
> int dllfunc ()
> { /* 0x5f4 */
> /* file /home/kewarken/61/test/libdll.c line 7 addr 0x5f4 */
> /* file /home/kewarken/61/test/libdll.c line 8 addr 0x608 */
> /* file /home/kewarken/61/test/libdll.c line 9 addr 0x60c */
> /* file /home/kewarken/61/test/libdll.c line 10 addr 0x614 */
> } /* 0x62c */
> 
> ***NEW***
> int blah /* 0x17e8 */;
> unsigned int some_global /* 0x17ec */;
> int dllfunc ()
> { /* 0x0 */
> /* file /61/home/kewarken/test/ppc-630/blah/../../libdll.c line 7 addr 
> 0x0 */
> /* file /61/home/kewarken/test/ppc-630/blah/../../libdll.c line 8 addr 
> 0x14 */
> /* file /61/home/kewarken/test/ppc-630/blah/../../libdll.c line 9 addr 
> 0x18 */
> /* file /61/home/kewarken/test/ppc-630/blah/../../libdll.c line 10 addr 
> 0x20 */
> } /* 0x38 */
> 
> 
> 

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer



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