From: Martin Liska <mliska@suse.cz>
Date: Mon, 5 Oct 2020 16:03:08 +0000 (+0200)
Subject: lto: fix LTO debug sections copying.
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=190c04ba36d9c6c3dce41f12012aa97c6d7f22f5;p=gcc.git

lto: fix LTO debug sections copying.

readelf -S prints:

There are 81999 section headers, starting at offset 0x1f488060:

Section Headers:
  [Nr] Name              Type            Address          Off    Size   ES Flg Lk Inf Al
  [ 0]                   NULL            0000000000000000 000000 01404f 00     81998   0  0
  [ 1] .group            GROUP           0000000000000000 000040 000008 04     81995 105027  4
...
  [81995] .symtab           SYMTAB          0000000000000000 d5d9298 2db310 18     81997 105026  8
  [81996] .symtab_shndx     SYMTAB SECTION INDICES 0000000000000000 d8b45a8 079dd8 04     81995   0  4
  [81997] .strtab           STRTAB          0000000000000000 d92e380 80460c 00      0   0  1
...

Looking at the documentation:
Table 7–15 ELF sh_link and sh_info Interpretation

sh_type - sh_link
SHT_SYMTAB - The section header index of the associated string table.
SHT_SYMTAB_SHNDX - The section header index of the associated symbol table.

As seen, sh_link of a SHT_SYMTAB always points to a .strtab and readelf
confirms that.

So we need to use reverse mapping taken from
  [81996] .symtab_shndx     SYMTAB SECTION INDICES 0000000000000000 d8b45a8 079dd8 04     81995   0  4

where sh_link points to 81995.

libiberty/ChangeLog:

	PR lto/97290
	* simple-object-elf.c (simple_object_elf_copy_lto_debug_sections):
	Use sh_link of a .symtab_shndx section.
---

diff --git a/libiberty/simple-object-elf.c b/libiberty/simple-object-elf.c
index 7c9d492f6a4..37e73348cb7 100644
--- a/libiberty/simple-object-elf.c
+++ b/libiberty/simple-object-elf.c
@@ -1191,7 +1191,7 @@ simple_object_elf_copy_lto_debug_sections (simple_object_read *sobj,
 	  unsigned int sh_link;
 	  sh_link = ELF_FETCH_FIELD (type_functions, ei_class, Shdr,
 				     shdr, sh_link, Elf_Word);
-	  symtab_indices_shndx[sh_link - 1] = i;
+	  symtab_indices_shndx[sh_link - 1] = i - 1;
 	  /* Always discard the extended index sections, after
 	     copying it will not be needed.  This way we don't need to
 	     update it and deal with the ordering constraints of
@@ -1372,19 +1372,22 @@ simple_object_elf_copy_lto_debug_sections (simple_object_read *sobj,
 	{
 	  unsigned entsize = ELF_FETCH_FIELD (type_functions, ei_class, Shdr,
 					      shdr, sh_entsize, Elf_Addr);
-	  unsigned strtab = ELF_FETCH_FIELD (type_functions, ei_class, Shdr,
-					     shdr, sh_link, Elf_Word);
 	  size_t prevailing_name_idx = 0;
 	  unsigned char *ent;
 	  unsigned *shndx_table = NULL;
 	  /* Read the section index table if present.  */
 	  if (symtab_indices_shndx[i - 1] != 0)
 	    {
-	      unsigned char *sidxhdr = shdrs + (strtab - 1) * shdr_size;
+	      unsigned char *sidxhdr = shdrs + symtab_indices_shndx[i - 1] * shdr_size;
 	      off_t sidxoff = ELF_FETCH_FIELD (type_functions, ei_class, Shdr,
 					       sidxhdr, sh_offset, Elf_Addr);
 	      size_t sidxsz = ELF_FETCH_FIELD (type_functions, ei_class, Shdr,
 					       sidxhdr, sh_size, Elf_Addr);
+	      unsigned int shndx_type
+		= ELF_FETCH_FIELD (type_functions, ei_class, Shdr,
+				   sidxhdr, sh_type, Elf_Word);
+	      if (shndx_type != SHT_SYMTAB_SHNDX)
+		return "Wrong section type of a SYMTAB SECTION INDICES section";
 	      shndx_table = (unsigned *)XNEWVEC (char, sidxsz);
 	      simple_object_internal_read (sobj->descriptor,
 					   sobj->offset + sidxoff,