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

1 files changed, 2 insertions, 0 deletions

diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index b6974e3173aa..bca719b2104b 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;