objtool: Optimize find_rela_by_dest_range()

Perf shows there is significant time in find_rela_by_dest(); this is
because we have to iterate the address space per byte, looking for
relocation entries.

Optimize this by reducing the address space granularity.

This reduces objtool on vmlinux.o runtime from 4.8 to 4.4 seconds.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lkml.kernel.org/r/20200324160924.861321325@infradead.org

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index 8a0a1bc18cd7d9ec477b3fc8f6df49722a617889..09ddc8f1def3cf328d3b5531391b4fc00a43804a 100644 (file)
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -215,7 +215,7 @@ struct symbol *find_symbol_by_name(struct elf *elf, const char *name)
 struct rela *find_rela_by_dest_range(struct elf *elf, struct section *sec,
                                     unsigned long offset, unsigned int len)
 {
-       struct rela *rela;
+       struct rela *rela, *r = NULL;
        unsigned long o;
 
        if (!sec->rela)
@@ -223,12 +223,19 @@ struct rela *find_rela_by_dest_range(struct elf *elf, struct section *sec,
 
        sec = sec->rela;
 
-       for (o = offset; o < offset + len; o++) {
+       for_offset_range(o, offset, offset + len) {
                hash_for_each_possible(elf->rela_hash, rela, hash,
                                       sec_offset_hash(sec, o)) {
-                       if (rela->sec == sec && rela->offset == o)
-                               return rela;
+                       if (rela->sec != sec)
+                               continue;
+
+                       if (rela->offset >= offset && rela->offset < offset + len) {
+                               if (!r || rela->offset < r->offset)
+                                       r = rela;
+                       }
                }
+               if (r)
+                       return r;
        }
 
        return NULL;

diff --git a/tools/objtool/elf.h b/tools/objtool/elf.h
index dfd2431ef693263a389fe6b501cac2ab8d8a2f6a..ebbb10c61e246743e3b2be05f4b9098e02013600 100644 (file)
--- a/tools/objtool/elf.h
+++ b/tools/objtool/elf.h
@@ -83,9 +83,23 @@ struct elf {
        DECLARE_HASHTABLE(rela_hash, 20);
 };
 
+#define OFFSET_STRIDE_BITS     4
+#define OFFSET_STRIDE          (1UL << OFFSET_STRIDE_BITS)
+#define OFFSET_STRIDE_MASK     (~(OFFSET_STRIDE - 1))
+
+#define for_offset_range(_offset, _start, _end)                \
+       for (_offset = ((_start) & OFFSET_STRIDE_MASK); \
+            _offset <= ((_end) & OFFSET_STRIDE_MASK);  \
+            _offset += OFFSET_STRIDE)
+
 static inline u32 sec_offset_hash(struct section *sec, unsigned long offset)
 {
-       u32 ol = offset, oh = offset >> 32, idx = sec->idx;
+       u32 ol, oh, idx = sec->idx;
+
+       offset &= OFFSET_STRIDE_MASK;
+
+       ol = offset;
+       oh = offset >> 32;
 
        __jhash_mix(ol, oh, idx);