On Tue, Jan 22, 2013 at 08:53:46PM +0100, Jan Kratochvil wrote:
> On Tue, 22 Jan 2013 19:19:04 +0100, Mark Wielaard wrote:
> > On Tue, Jan 22, 2013 at 06:28:03PM +0100, Jan Kratochvil wrote:
> > > This is OK as long as there cannot happen:
> > > mod->first_global == 0 && mod->aux_symdata != NULL
> > > and therefore also: mod->aux_first_global > 0
> >
> > If that happens then first_global = 0. Which means we just don't know
> > where the first global is in the table. And so we will just search the
> > whole table (1, syments). That means we just don't do the optimization
>
> It has functionality impact, that means we will ignore the first global symbol
> of minidebuginfo as search_table will be called with (1, syments) as you say
> but in such case symbol #0 is a valid one - from minidebuginfo (shifted to
> number #1 there).
That could only happen if also mod->syments = 0, aka there is no dynsym at
all. But then we will not get here, because...
> Yes, and this is a bug. In the testcase below are perfectly valid shdrs.
>
> 1003 case DWFL_E_NO_SYMTAB:
> 1004 if (symscn != NULL)
> 1005 {
> 1006 /* We still have the dynamic symbol table. */
> 1007 mod->symerr = DWFL_E_NOERROR;
> 1008
> 1009 /* The dynsym table might be extended by an auxiliary
> table. */
> 1010 find_aux_sym (mod, &aux_symscn, &aux_xndxscn,
> &aux_strshndx);
> 1011 break;
> 1012 }
>
> minidebuginfo may exist even if there is no .symtab/.dynsym and therefore
> SYMSCN == NULL.
>
> Attached such example.
>
> echo 'int main (void) { return 0; }' >3.c
> gcc -o 3 3.c -Wall -static -s
> objcopy --add-section
> .gnu_debugdata=/path/to/gdb/testsuite/gdb.base/gnu-debugdata.mini_debuginfo.xz
> 3
>
> GDB in such cas displays symbols from minidebuginfo correctly (it complains
> a bit as this testcase is unclean but the purpose works).
>
> But dwfl_module_getsymtab() returns 0.
Right. The code indeed assumes that the auxiliary table is always in addition
to a
minimal dynsym table. Thanks for the testcase, I can see if it is easy to
support it with
aux table == full table.
I do wonder how realistic it is that we will ever encounter such a case though.
Is
this very contrived or do you think people will actually use .gnu_debugdata
this way?
Thanks,
Mark
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