[Bug gdb/29295] [gdb] out of bounds access in objfile::section_offset

["vries at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=29295

--- Comment #7 from Tom de Vries <vries at gcc dot gnu.org> ---
Created attachment 14203
  --> https://sourceware.org/bugzilla/attachment.cgi?id=14203&action=edit
WIP patch

I'm now trying a less ambitious approach.

Rather than trying to completely accommodate the newly created section, just
try to get the indexing right for the old sections.

So, if we start out with 6 bfd sections, meaning 10 gdb sections, then the ind
section is at 9.

Then a new bfd section is added, and now it's ambiguous: does 9 refer to the
ind section (6+3), or the abs section (7+2)?

We try to resolve this ambiguity by making gdb_bfd_section_index independent
from bfd_count_sections:
...
   else if (section == bfd_com_section_ptr)
-    return bfd_count_sections (abfd);
+    return INT_MAX - 3;
   else if (section == bfd_und_section_ptr)
-    return bfd_count_sections (abfd) + 1;
+    return INT_MAX - 2;
   else if (section == bfd_abs_section_ptr)
-    return bfd_count_sections (abfd) + 2;
+    return INT_MAX - 1;
   else if (section == bfd_ind_section_ptr)
-    return bfd_count_sections (abfd) + 3;
+    return INT_MAX;
...

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