| Summary: | fake symbols to aid debugging | ||
|---|---|---|---|
| Product: | gdb | Reporter: | Alan Modra <amodra> |
| Component: | symtab | Assignee: | Not yet assigned to anyone <unassigned> |
| Status: | RESOLVED WONTFIX | ||
| Severity: | enhancement | CC: | gdb-prs |
| Priority: | P3 | ||
| Version: | unknown | ||
| Target Milestone: | --- | ||
| Host: | Target: | ||
| Build: | Last reconfirmed: | ||
Into the too hard basket for this one. |
[Converted from Gnats 1327] PowerPC64 (and other architechures) use linker stubs for various things, most notably to make calls to functions in shared objects. Typical disassembly looks like: the stub 7ea138: 3d 82 00 01 addis r12,r2,1 7ea13c: f8 41 00 28 std r2,40(r1) 7ea140: e9 6c 11 88 ld r11,4488(r12) 7ea144: e8 4c 11 90 ld r2,4496(r12) 7ea148: 7d 69 03 a6 mtctr r11 7ea14c: e9 6c 11 98 ld r11,4504(r12) 7ea150: 4e 80 04 20 bctr call to stub 87d6f0: e8 7e 80 90 ld r3,-32624(r30) 87d6f4: 4b f6 ca 45 bl 7ea138 <._init+0xe9b8> 87d6f8: e8 41 00 28 ld r2,40(r1) Note the meaningless symbol given as target for the "bl". Now, if you know enough about the ABI, it's possible to figure out which function is being called, but that's a pain. In the case of PowerPC64 you need to a) Find the value of r2 by looking at the calling function's opd entry. (with multiple GOT/TOC r2 is not fixed). b) Perform the calculation done by the stub to find the plt entry address. c) Search the relocs to find the one for this particular plt entry. The symbol on the reloc gives the function name. I waste enough time doing this that I figure it's worth doing something about it. My first idea, already implemented, was to have the linker emit extra symbols to identify the stubs. This works well but bloats the symbol table and isn't on by default. A better idea would be to create the stub symbols on the fly. With that in mind, I propose to add two new bfd functions long bfd_get_fake_symtab_upper_bound (bfd *abfd); long bfd_canonicalize_fake_symtab (bfd *abfd, asymbol **buf); analogous to bfd_get_symtab_upper_bound and bfd_canonicalize_symtab. Comments? -- Alan Modra IBM OzLabs - Linux Technology Centre Release: unknown