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Re: Shared library call problems on PowerPC with current binutils/gdb
- From: Daniel Jacobowitz <drow at false dot org>
- To: Ulrich Weigand <uweigand at de dot ibm dot com>, gdb-patches at sourceware dot org, bauerman at br dot ibm dot com, amodra at bigpond dot net dot au
- Date: Fri, 2 May 2008 17:51:32 -0400
- Subject: Re: Shared library call problems on PowerPC with current binutils/gdb
- References: <200804282253.m3SMrwQF005602@d12av02.megacenter.de.ibm.com> <20080429003951.GA30324@caradoc.them.org>
On Mon, Apr 28, 2008 at 08:39:51PM -0400, Daniel Jacobowitz wrote:
> On Tue, Apr 29, 2008 at 12:53:58AM +0200, Ulrich Weigand wrote:
> > - Extend elf_symtab_read to treat a synthetic symbol XXX@plt as a
> > mst_solib_trampoline symbol for XXX.
>
> Sounds reasonable. I suggested this to Aleksandar for another
> problem, even :-) Though it was kind of nice to have it show up in
> disassembly with @plt; will it still do that? It's nice to know
> immediately when I'm looking at the PLT stub instead of the
> definition.
This appears to work consistently, where by work I mean disassembly
shows the @plt sym but breakpoints on the undecorated version work
fine. I'm not sure exactly why; it may be luck. If it's luck
and someone cares later, we could make it work reliably by making
sure the @plt version has an accurate size and the non-@plt version
has size 0, or by making lookup_minimal_symbol_by_pc_section
explicitly prefer text to non-text symbols.
Hmm, thinking about this more, it probably won't work for your
case after all. lookup_solib_trampoline_symbol_by_pc will return
NULL if the first symbol we find is the text version.
What do you think? I wrote this because I need it to get some symbol
for malloc on Symbian, where I do not have a symbol file corresponding
to libc. The PLT entry works nicely for that purpose.
--
Daniel Jacobowitz
CodeSourcery
2008-05-02 Daniel Jacobowitz <dan@codesourcery.com>
* elfread.c (elf_symtab_read): Create trampolines for @plt symbols.
Index: symbian-fsf/gdb/elfread.c
===================================================================
--- symbian-fsf.orig/gdb/elfread.c 2008-05-02 16:56:20.000000000 -0400
+++ symbian-fsf/gdb/elfread.c 2008-05-02 17:34:42.000000000 -0400
@@ -521,6 +521,33 @@ elf_symtab_read (struct objfile *objfile
if (msym != NULL)
msym->filename = filesymname;
gdbarch_elf_make_msymbol_special (gdbarch, sym, msym);
+
+ /* For @plt symbols, also record a trampoline to the
+ destination symbol. The @plt symbol will be used in
+ disassembly, and the trampoline will be used when we are
+ trying to find the target. */
+ if (msym && ms_type == mst_text && type == ST_SYNTHETIC)
+ {
+ int len = strlen (sym->name);
+
+ if (len > 4 && strcmp (sym->name + len - 4, "@plt") == 0)
+ {
+ char *base_name = alloca (len - 4 + 1);
+ struct minimal_symbol *mtramp;
+
+ memcpy (base_name, sym->name, len - 4);
+ base_name[len - 4] = '\0';
+ mtramp = record_minimal_symbol (base_name, symaddr,
+ mst_solib_trampoline,
+ sym->section, objfile);
+ if (mtramp)
+ {
+ MSYMBOL_SIZE (mtramp) = MSYMBOL_SIZE (msym);
+ mtramp->filename = filesymname;
+ gdbarch_elf_make_msymbol_special (gdbarch, sym, mtramp);
+ }
+ }
+ }
}
}
}