Re: RFC: Supporting multiple relocs per section

[Nick Clifton <nickc at redhat dot com>]

Hi Alan,

> On Fri, Feb 14, 2020 at 10:30:47AM +0000, Nick Clifton wrote:
>>   As part of this process I also discovered that the BFD library would
>>   unconditionally convert OS-specific and PROC-specific section indices
>>   into SHN_ABS indices when writing out symbol tables,

> That sounds like a bug that should be fixed for all ELF targets and
> not via a target hook.  
I have checked in this patch to resolve this particular problem.  I do not 
think that the code has to worry about the sign extension of the special
values as this has been handled by the definitions in elf/internal.h.

Cheers
  Nick

bfd/ChangeLog
2020-02-20  Nick Clifton  <nickc@redhat.com>

	* elf-bfd.h (struct elf_backend_data): Add symbol_section_index
	callback.
	* elfxx-target.h (elf_backend_symbol_section_index): Provide
	default definition.
	(elfNN_bed): Initialise the symbol_section_index field.
	* elf.c (swap_out_syms): Call symbol_section_index, if defined, on
	OS and PROC specific section indicies.  Warn if converting other
	reserved incidies to SHN_ABS.

diff --git a/bfd/elf-bfd.h b/bfd/elf-bfd.h
index cbbba153f4..7d36e23ea1 100644
--- a/bfd/elf-bfd.h
+++ b/bfd/elf-bfd.h
@@ -1503,6 +1503,12 @@ struct elf_backend_data
   /* Opcode representing no unwind.  */
   int (*cant_unwind_opcode) (struct bfd_link_info *);
 
+  /* Called when emitting an ELF symbol whoes input version had an
+     ST_SHNDX field set to a value in the range SHN_LOPROC..SHN_HIOS.
+     Returns the value to be installed in the ST_SHNDX field of the
+     emitted symbol.  If not defined, the value is left unchanged.  */
+  unsigned int (*symbol_section_index) (bfd *, elf_symbol_type *);
+  
   /* This is non-zero if static TLS segments require a special alignment.  */
   unsigned static_tls_alignment;
 
diff --git a/bfd/elf.c b/bfd/elf.c
index deb93b0a5a..4342e84752 100644
--- a/bfd/elf.c
+++ b/bfd/elf.c
@@ -8194,9 +8194,26 @@ swap_out_syms (bfd *abfd,
 		  if (elf_symtab_shndx_list (abfd))
 		    shndx = elf_symtab_shndx_list (abfd)->ndx;
 		  break;
-		default:
+		case SHN_COMMON:
+		case SHN_ABS:
 		  shndx = SHN_ABS;
 		  break;
+		default:
+		  if (shndx >= SHN_LOPROC && shndx <= SHN_HIOS)
+		    {
+		      if (bed->symbol_section_index)
+			shndx = bed->symbol_section_index (abfd, type_ptr);
+		      /* Otherwise just leave the index alone.  */
+		    }
+		  else
+		    {
+		      if (shndx > SHN_HIOS && shndx < SHN_HIRESERVE)
+			_bfd_error_handler (_("%pB: \
+Unable to handle section index %x in ELF symbol.  Using ABS instead."),
+					  abfd, shndx);
+		      shndx = SHN_ABS;
+		    }
+		  break;
 		}
 	    }
 	  else
diff --git a/bfd/elfxx-target.h b/bfd/elfxx-target.h
index caca83f5c9..e9cac0a535 100644
--- a/bfd/elfxx-target.h
+++ b/bfd/elfxx-target.h
@@ -769,6 +769,10 @@
 #define elf_backend_cant_unwind_opcode 0
 #endif
 
+#ifndef elf_backend_symbol_section_index
+#define elf_backend_symbol_section_index NULL
+#endif
+ 
 #ifndef elf_match_priority
 #define elf_match_priority \
   (ELF_ARCH == bfd_arch_unknown ? 2 : ELF_OSABI == ELFOSABI_NONE ? 1 : 0)
@@ -895,6 +899,7 @@ static struct elf_backend_data elfNN_bed =
   elf_backend_fixup_gnu_properties,
   elf_backend_compact_eh_encoding,
   elf_backend_cant_unwind_opcode,
+  elf_backend_symbol_section_index,
   elf_backend_static_tls_alignment,
   elf_backend_stack_align,
   elf_backend_strtab_flags,