x86: Cache the symbol table when packing relative relocations

When packing relative relocations, x86 linker may load the same symbol
table repeatedly, which can take a long time.  On Intel Core i7-1195G7
with 32GB RAM, it takes more than 45 minutes to create an output with
-pie -z pack-relative-relocs from an input with 208025 code sections.
Cache the symbol table to reduce the link time to less than 2 seconds.

On the same machine, creating 3.1GB clang executable in LLVM 21.1.3 debug
build:

user            55.39 seconds
system          6.71 seconds
total           65.80 seconds
maximum set(GB) 10.43
page faults     2406941

	PR ld/33765
	* elfxx-x86.c (elf_x86_relative_reloc_record_add): Remove
	keep_symbuf_p.
	(_bfd_x86_elf_link_relax_section): Updated.  Cache the symbol
	table to avoid loading it again.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>

diff --git a/bfd/elfxx-x86.c b/bfd/elfxx-x86.c
index 36ba7919f47ea53a8ef51363c4b46f193214e847..fc51bf262a510aa97482ff8c9c586915baa7cfa0 100644 (file)
--- a/bfd/elfxx-x86.c
+++ b/bfd/elfxx-x86.c
@@ -1011,7 +1011,7 @@ elf_x86_relative_reloc_record_add
    struct elf_x86_relative_reloc_data *relative_reloc,
    Elf_Internal_Rela *rel, asection *sec,
    asection *sym_sec, struct elf_link_hash_entry *h,
-   Elf_Internal_Sym *sym, bfd_vma offset, bool *keep_symbuf_p)
+   Elf_Internal_Sym *sym, bfd_vma offset)
 {
   bfd_size_type newidx;
 
@@ -1055,8 +1055,6 @@ elf_x86_relative_reloc_record_add
     {
       relative_reloc->data[newidx].sym = sym;
       relative_reloc->data[newidx].u.sym_sec = sym_sec;
-      /* We must keep the symbol buffer since SYM will be used later.  */
-      *keep_symbuf_p = true;
     }
   relative_reloc->data[newidx].offset = offset;
   relative_reloc->data[newidx].address = 0;
@@ -1079,7 +1077,7 @@ _bfd_x86_elf_link_relax_section (bfd *abfd ATTRIBUTE_UNUSED,
   Elf_Internal_Shdr *symtab_hdr;
   Elf_Internal_Rela *internal_relocs;
   Elf_Internal_Rela *irel, *irelend;
-  Elf_Internal_Sym *isymbuf = NULL;
+  Elf_Internal_Sym *isymbuf;
   struct elf_link_hash_entry **sym_hashes;
   elf_backend_data *bed;
   struct elf_x86_link_hash_table *htab;
@@ -1087,7 +1085,6 @@ _bfd_x86_elf_link_relax_section (bfd *abfd ATTRIBUTE_UNUSED,
   bool is_x86_64;
   bool unaligned_section;
   bool return_status = false;
-  bool keep_symbuf = false;
 
   /* Assume we're not going to change any sizes, and we'll only need
      one pass.  */
@@ -1131,6 +1128,23 @@ _bfd_x86_elf_link_relax_section (bfd *abfd ATTRIBUTE_UNUSED,
   if (internal_relocs == NULL)
     return false;
 
+  isymbuf = (Elf_Internal_Sym *) symtab_hdr->contents;
+  if (isymbuf == NULL && symtab_hdr->sh_info > 1)
+    {
+      /* symtab_hdr->sh_info == the number of local symbols + 1.  Load
+        the symbol table if there are local symbols.  */
+      isymbuf = bfd_elf_get_elf_syms (abfd, symtab_hdr,
+                                     symtab_hdr->sh_info,
+                                     0, NULL, NULL, NULL);
+      if (isymbuf == NULL)
+       return false;
+
+      /* Cache the symbol table to avoid loading the same symbol table
+        repeatedly which can take a long time if the input has many
+        code sections.  */
+      symtab_hdr->contents = (unsigned char *) isymbuf;
+    }
+
   irelend = internal_relocs + input_section->reloc_count;
   for (irel = internal_relocs; irel < irelend; irel++)
     {
@@ -1163,20 +1177,6 @@ _bfd_x86_elf_link_relax_section (bfd *abfd ATTRIBUTE_UNUSED,
 
       if (r_symndx < symtab_hdr->sh_info)
        {
-         /* Read this BFD's local symbols.  */
-         if (isymbuf == NULL)
-           {
-             isymbuf = (Elf_Internal_Sym *) symtab_hdr->contents;
-             if (isymbuf == NULL)
-               {
-                 isymbuf = bfd_elf_get_elf_syms (abfd, symtab_hdr,
-                                                 symtab_hdr->sh_info,
-                                                 0, NULL, NULL, NULL);
-                 if (isymbuf == NULL)
-                   goto error_return;
-               }
-           }
-
          isym = isymbuf + r_symndx;
          switch (isym->st_shndx)
            {
@@ -1278,8 +1278,7 @@ _bfd_x86_elf_link_relax_section (bfd *abfd ATTRIBUTE_UNUSED,
          if (!elf_x86_relative_reloc_record_add (info,
                                                  &htab->relative_reloc,
                                                  irel, htab->elf.sgot,
-                                                 sec, h, isym, offset,
-                                                 &keep_symbuf))
+                                                 sec, h, isym, offset))
            goto error_return;
 
          continue;
@@ -1348,8 +1347,7 @@ _bfd_x86_elf_link_relax_section (bfd *abfd ATTRIBUTE_UNUSED,
                 ((unaligned_section || unaligned_offset)
                  ? &htab->unaligned_relative_reloc
                  : &htab->relative_reloc),
-                irel, input_section, sec, h, isym, offset,
-                &keep_symbuf))
+                irel, input_section, sec, h, isym, offset))
            goto error_return;
        }
     }
@@ -1359,14 +1357,6 @@ _bfd_x86_elf_link_relax_section (bfd *abfd ATTRIBUTE_UNUSED,
   return_status = true;
 
 error_return:
-  if ((unsigned char *) isymbuf != symtab_hdr->contents)
-    {
-      /* Cache the symbol buffer if it must be kept.  */
-      if (keep_symbuf)
-       symtab_hdr->contents = (unsigned char *) isymbuf;
-      else
-       free (isymbuf);
-    }
   if (elf_section_data (input_section)->relocs != internal_relocs)
     free (internal_relocs);
   return return_status;