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@alien8.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/Y2LlRA7x+8UsE1xf@hirez.programming.kicks-ass.net

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 3d636d12d679f6f093335f59c637f17aab53bbc8..8cd7f018002c56dc08fe576706ef5b10622fb6e3 100644 (file)
--- 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 b6974e3173aa59169a540608b2c4d2d08f058dc9..bca719b2104b8a958395b0c2766755b966a53f1e 100644 (file)
--- 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;