The following commit has been merged into the x86/core branch of tip: Commit-ID: 19526717f768bf2f89ca01bd2a595728ebe57540 Gitweb: https://git.kernel.org/tip/19526717f768bf2f89ca01bd2a595728ebe57540 Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx> AuthorDate: Wed, 02 Nov 2022 22:31:19 +01:00 Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx> CommitterDate: Sat, 05 Nov 2022 11:28:02 +01:00 objtool: Optimize elf_dirty_reloc_sym() When moving a symbol in the symtab its index changes and any reloc referring that symtol-table-index will need to be rewritten too. In order to facilitate this, objtool simply marks the whole reloc section 'changed' which will cause the whole section to be re-generated. However, finding the relocs that use any given symbol is implemented rather crudely -- a fully iteration of all sections and their relocs. Given that some builds have over 20k sections (kallsyms etc..) iterating all that for *each* symbol moved takes a bit of time. Instead have each symbol keep a list of relocs that reference it. This *vastly* improves build times for certain configs. Reported-by: Borislav Petkov <bp@xxxxxxxxx> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> Link: https://lkml.kernel.org/r/Y2LlRA7x+8UsE1xf@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx --- tools/objtool/elf.c | 27 ++++++++++----------------- tools/objtool/include/objtool/elf.h | 2 ++ 2 files changed, 12 insertions(+), 17 deletions(-) diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c index 3d636d1..8cd7f01 100644 --- a/tools/objtool/elf.c +++ b/tools/objtool/elf.c @@ -356,6 +356,7 @@ static void elf_add_symbol(struct elf *elf, struct symbol *sym) struct rb_node *pnode; struct symbol *iter; + INIT_LIST_HEAD(&sym->reloc_list); INIT_LIST_HEAD(&sym->pv_target); sym->alias = sym; @@ -557,6 +558,7 @@ int elf_add_reloc(struct elf *elf, struct section *sec, unsigned long offset, reloc->sym = sym; reloc->addend = addend; + list_add_tail(&reloc->sym_reloc_entry, &sym->reloc_list); list_add_tail(&reloc->list, &sec->reloc->reloc_list); elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc)); @@ -573,21 +575,10 @@ int elf_add_reloc(struct elf *elf, struct section *sec, unsigned long offset, */ static void elf_dirty_reloc_sym(struct elf *elf, struct symbol *sym) { - struct section *sec; - - list_for_each_entry(sec, &elf->sections, list) { - struct reloc *reloc; - - if (sec->changed) - continue; + struct reloc *reloc; - list_for_each_entry(reloc, &sec->reloc_list, list) { - if (reloc->sym == sym) { - sec->changed = true; - break; - } - } - } + list_for_each_entry(reloc, &sym->reloc_list, sym_reloc_entry) + reloc->sec->changed = true; } /* @@ -902,11 +893,12 @@ static int read_rela_reloc(struct section *sec, int i, struct reloc *reloc, unsi static int read_relocs(struct elf *elf) { + unsigned long nr_reloc, max_reloc = 0, tot_reloc = 0; struct section *sec; struct reloc *reloc; - int i; unsigned int symndx; - unsigned long nr_reloc, max_reloc = 0, tot_reloc = 0; + struct symbol *sym; + int i; if (!elf_alloc_hash(reloc, elf->text_size / 16)) return -1; @@ -947,13 +939,14 @@ static int read_relocs(struct elf *elf) reloc->sec = sec; reloc->idx = i; - reloc->sym = find_symbol_by_index(elf, symndx); + reloc->sym = sym = find_symbol_by_index(elf, symndx); if (!reloc->sym) { WARN("can't find reloc entry symbol %d for %s", symndx, sec->name); return -1; } + list_add_tail(&reloc->sym_reloc_entry, &sym->reloc_list); list_add_tail(&reloc->list, &sec->reloc_list); elf_hash_add(reloc, &reloc->hash, reloc_hash(reloc)); diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h index b6974e3..bca719b 100644 --- a/tools/objtool/include/objtool/elf.h +++ b/tools/objtool/include/objtool/elf.h @@ -62,6 +62,7 @@ struct symbol { u8 fentry : 1; u8 profiling_func : 1; struct list_head pv_target; + struct list_head reloc_list; }; struct reloc { @@ -73,6 +74,7 @@ struct reloc { }; struct section *sec; struct symbol *sym; + struct list_head sym_reloc_entry; unsigned long offset; unsigned int type; s64 addend;
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