Design problem with min sym relocation?
Elena Zannoni
ezannoni@redhat.com
Fri Nov 8 14:58:00 GMT 2002
Joel Brobecker writes:
> This is something I found out a while ago, and forgot to mention it
> here. It happens on alpha-osf, but this is probably a general issue.
>
> The current version of GDB used at ACT is based on GDB 5.1.1. We get
> an internal error when doing the following on Tru64 4.0f:
>
> (gdb) file /usr/shlib/libm.so
> Reading symbols from /usr/shlib/libm.so...mdebugread.c:2445:
> gdb-internal-error: sect_index_data not initialized
>
> An internal GDB error was detected. This may make further
> debugging unreliable. Quit this debugging session? (y or n)
>
> This is caused by a symbol called "signgam" which is located in the
> .sdata section. The problem is that GDB seems to be insisting on
> coalescing all .*data sections in the same lot, if I understand
> parse_partial_symbols in mdebugread.c correctly:
>
> else if (SC_IS_DATA (ext_in->asym.sc))
> {
> ms_type = mst_data;
> svalue += ANOFFSET (objfile->section_offsets,
> SECT_OFF_DATA (objfile));
> }
>
> (SC_IS_DATA matches data, sdata, pdata, etc sections)
>
> I think this code snipet shows 2 problems:
> 1. We relocated based on the .data section. In our case, 2e should
> relocate relative to the .sdata section. That would be quite
> easy to fix.
> 2. ms_type is set to mst_data. This seems to be later used by
> prim_record_minimal_symbol vis:
>
> case mst_data:
> case mst_file_data:
> section = SECT_OFF_DATA (objfile);
>
> This would be a bit more difficult to fix without adding new
> enum values for each data section kind.
>
> I tried reproducing this problem on Tru64 5.1a, but this time with no
> luck. I checked this symbol, and it is still there, and still in the
> .sdata section. But this time, the shared object has a .data section.
> So my bet is that GDB computes temporarily gets away with the problem
> this time, but computes an incorrect address for this symbol.
>
> I tried with a more recent version of the code, and the internal error
> is gone. I don't know if I should rejoyce or not, as I still see the
> piece of code that I pasted above.
>
> This is all based on code inspection (cruelly lacking the time to look
> more into the problem), but I think there is still a latent problem
> where we compute incorrect addresses for certain symbols located in non
> mainstream sections (like in the .sdata instead of the .data section).
>
> I would greatly appreciate your thoughs on the issue. My view is that
> we should get rid of these SC_IS_* and SECT_OFF_* macros, add new
> mst_* enums (one for each section kind), and add services that
> compute the ms_type from the section kind, and compute the section
> index of a given ms_type. This would give us something like:
Yes. I remember looking at another similar problem in mdebugread.c for
which the solution was to split SC_IS_BSS and add a new, more
precise SC_IS_SBSS.
[goes look....hey it was you! :)]
http://sources.redhat.com/ml/gdb-patches/2001-06/msg00244.html
Would a similar approach help in this case?
Definitely the SECT_OFF should eventually go. I guess I can call that a
pipe-dream.
Elena
>
> ms_type = get_ms_type_from_storage_class (ext_in->asym.sc);
> svalue += ANOFFSET (objfile->section_offsets, section_index (ms_type));
>
> in mdebugread.c (should move the big ifs list out of parse_partial_symbols),
> and then something like this in prim_record_minimal_symbol():
>
> section = section_index (ms_type);
>
> At the time when I looked at this, I did not start this conversion
> because I thought it might touch a large number of file, which I am always
> reluctant to do before getting any feedback, especially when it touches
> the current design.
> --
> Joel
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