[Bug libdw/31447] New: Provide a public debug section relocation function

[mark at klomp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31447

Bug ID: 31447
   Summary: Provide a public debug section relocation function
   Product: elfutils
   Version: unspecified
Status: NEW
  Severity: normal
  Priority: P2
 Component: libdw
  Assignee: unassigned at sourceware dot org
  Reporter: mark at klomp dot org
CC: elfutils-devel at sourceware dot org
  Target Milestone: ---

When opening an ET_REL file with dwarf_begin no relocations are resolved and no
error checking is done if that is necessary. Causing some functions to produce
errors or wrong results (because an index is wrongly assumed to be zero).

When opening such a file through libdwfl we do resolve all cross-debug-section
relocations using __libdwfl_relocate.

It would be good to make this a public function. Maybe through libdwelf
dwelf_relocation_debug_sections (Elf *elf). So users can make sure ET_REL files
can be handled by libdw.

And maybe add a check/flag in dwarf_begin so an error can be produced if a
relocation value is needed for a correct result.

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[Bug libdw/31447] Provide a public debug section relocation function

[mark at klomp dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=31447

--- Comment #1 from Mark Wielaard  ---
This is the current "workaround" I use when working with individual ET_REL
DWARF files (also works for any other ELF type):

 static char *debuginfo_path = NULL;
 static const Dwfl_Callbacks dwfl_callbacks =
{
  .find_elf = dwfl_build_id_find_elf,
  .find_debuginfo = dwfl_standard_find_debuginfo,
  .section_address = dwfl_offline_section_address,
  .debuginfo_path = &debuginfo_path,
};

 int main (int argc, char **argv)
 {
Dwfl *dwfl = dwfl_begin (&dwfl_callbacks);
Dwfl_Module *module = dwfl_report_elf (dwfl, argv[1], argv[1], -1, 0,
false);
if (module == NULL)
  printf ("%s\n", dwfl_errmsg (-1));
dwfl_report_end (dwfl, NULL, NULL);

Dwarf_Addr bias;
Dwarf *dwarf = dwfl_module_getdwarf (module, &bias);
if (dwarf == NULL)
  printf ("%s\n", dwfl_errmsg (-1));

/* ... do something with dwarf ... */

dwfl_end (dwfl); // Also cleans up dwarf.
 }

But this is obviously a little cumbersome if not really using any other libdwfl
features.

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