Squash readelf warning on zero sh_link reloc section

[Alan Modra]

On readelf examining a static executable built with current glibc,
we get a silly warning.

Section Headers:
[Nr] Name Type Address Off Size ES Flg Lk Inf Al
[ 0] NULL 0000000000000000 000000 000000 00 0 0 0
[ 1] .note.ABI-tag NOTE 0000000000400190 000190 000020 00 A 0 0 4
[ 2] .note.gnu.build-id NOTE 00000000004001b0 0001b0 000024 00 A 0 0 4
readelf: Warning: [ 3]: Link field (0) should index a symtab section.
[ 3] .rela.plt RELA 00000000004001d8 0001d8 000228 18 AI 0 20 8

This .rela.plt section contains only IRELATIVE relocations (which have
symbol index zero), so it isn't appropriate to warn. A zero sh_link
section is deliberately chosen for such a section (see PR10337 and
PR23850).

So this patch disables the SHT_REL* sh_link warning. I've also
removed the .rel.dyn/.rela.dyn section name test to disable the
sh_info warning for SHT_REL* sections. While relocation sections in
an executable need not specify the section they relocate (the
relocation sh_offset field is an address, not a section offset), that
isn't true in a relocatable file where sh_offset is relative to a
section. If .rela.dyn happens to exist in an ET_REL object it must
specify a valid section.

* readelf.c (process_section_headers): Don't warn on a zero
sh_info or sh_link for any reloc section in an executable or
shared library. Do warn for .rel.dyn/.rela.dyn in ET_REL.

diff --git a/binutils/readelf.c b/binutils/readelf.c
index d8d0d6e954..39744009ab 100644
--- a/binutils/readelf.c
+++ b/binutils/readelf.c
@@ -6299,14 +6299,21 @@ process_section_headers (Filedata * filedata)
/* Check the sh_link field. */
switch (section->sh_type)
{
+ case SHT_REL:
+ case SHT_RELA:
+ if (section->sh_link == 0
+ && (filedata->file_header.e_type == ET_EXEC
+ || filedata->file_header.e_type == ET_DYN))
+ /* A dynamic relocation section where all entries use a
+ zero symbol index need not specify a symtab section. */
+ break;
+ /* Fall through. */
case SHT_SYMTAB_SHNDX:
case SHT_GROUP:
case SHT_HASH:
case SHT_GNU_HASH:
case SHT_GNU_versym:
- case SHT_REL:
- case SHT_RELA:
- if (section->sh_link < 1
+ if (section->sh_link == 0
|| section->sh_link >= filedata->file_header.e_shnum
|| (filedata->section_headers[section->sh_link].sh_type != SHT_SYMTAB
&& filedata->section_headers[section->sh_link].sh_type != SHT_DYNSYM))
@@ -6320,7 +6327,7 @@ process_section_headers (Filedata * filedata)
case SHT_GNU_verneed:
case SHT_GNU_verdef:
case SHT_GNU_LIBLIST:
- if (section->sh_link < 1
+ if (section->sh_link == 0
|| section->sh_link >= filedata->file_header.e_shnum
|| filedata->section_headers[section->sh_link].sh_type != SHT_STRTAB)
warn (_("[%2u]: Link field (%u) should index a string section.\n"),
@@ -6353,7 +6360,13 @@ process_section_headers (Filedata * filedata)
{
case SHT_REL:
case SHT_RELA:
- if (section->sh_info < 1
+ if (section->sh_info == 0
+ && (filedata->file_header.e_type == ET_EXEC
+ || filedata->file_header.e_type == ET_DYN))
+ /* Dynamic relocations apply to segments, so they do not
+ need to specify the section they relocate. */
+ break;
+ if (section->sh_info == 0
|| section->sh_info >= filedata->file_header.e_shnum
|| (filedata->section_headers[section->sh_info].sh_type != SHT_PROGBITS
&& filedata->section_headers[section->sh_info].sh_type != SHT_NOBITS
@@ -6363,21 +6376,8 @@ process_section_headers (Filedata * filedata)
&& filedata->section_headers[section->sh_info].sh_type != SHT_PREINIT_ARRAY
/* FIXME: Are other section types valid ? */
&& filedata->section_headers[section->sh_info].sh_type < SHT_LOOS))
- {
- if (section->sh_info == 0
- && (filedata->file_header.e_type == ET_EXEC
- || filedata->file_header.e_type == ET_DYN
- /* These next two tests may be redundant, but
- they have been left in for paranoia's sake. */
- || streq (SECTION_NAME (section), ".rel.dyn")
- || streq (SECTION_NAME (section), ".rela.dyn")))
- /* Dynamic relocations apply to segments, not sections, so
- they do not need an sh_info value. */
- ;
- else
- warn (_("[%2u]: Info field (%u) should index a relocatable section.\n"),
- i, section->sh_info);
- }
+ warn (_("[%2u]: Info field (%u) should index a relocatable section.\n"),
+ i, section->sh_info);
break;

case SHT_DYNAMIC: