diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2022-10-28 20:29:51 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2022-11-01 13:44:08 +0100 |
| commit | 13f60e80e15dd0657c90bcca372ba045630ed9de (patch) | |
| tree | 953847669387957ccbeb914739af7b1a222d2adb /tools/objtool/include | |
| parent | 4c91be8e926c6b3734d59b9348e305431484d42b (diff) | |
objtool: Avoid O(bloody terrible) behaviour -- an ode to libelf
Due to how gelf_update_sym*() requires an Elf_Data pointer, and how
libelf keeps Elf_Data in a linked list per section,
elf_update_symbol() ends up having to iterate this list on each
update to find the correct Elf_Data for the index'ed symbol.
By allocating one Elf_Data per new symbol, the list grows per new
symbol, giving an effective O(n^2) insertion time. This is obviously
bloody terrible.
Therefore over-allocate the Elf_Data when an extention is needed.
Except it turns out libelf disregards Elf_Scn::sh_size in favour of
the sum of Elf_Data::d_size. IOW it will happily write out all the
unused space and fill it with:
0000000000000000 0 NOTYPE LOCAL DEFAULT UND
entries (aka zeros). Which obviously violates the STB_LOCAL placement
rule, and is a general pain in the backside for not being the desired
behaviour.
Manually fix-up the Elf_Data size to avoid this problem before calling
elf_update().
This significantly improves performance when adding a significant
number of symbols.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Yujie Liu <yujie.liu@intel.com>
Link: https://lkml.kernel.org/r/20221028194453.461658986@infradead.org
Diffstat (limited to 'tools/objtool/include')
| -rw-r--r-- | tools/objtool/include/objtool/elf.h | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h index d28533106b78..9e96a613c50f 100644 --- a/tools/objtool/include/objtool/elf.h +++ b/tools/objtool/include/objtool/elf.h @@ -38,7 +38,7 @@ struct section { Elf_Data *data; char *name; int idx; - bool changed, text, rodata, noinstr, init; + bool changed, text, rodata, noinstr, init, truncate; }; struct symbol { |