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objtool/klp: Fix symbol correlation for orphaned local symbols

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When compiling with CONFIG_LTO_CLANG_THIN, vmlinux.o has
__irf_[start|end] before the first FILE entry:

  $ readelf -sW vmlinux.o
  Symbol table '.symtab' contains 597706 entries:
     Num:    Value          Size Type    Bind   Vis      Ndx Name
       0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND
       1: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT   18 __irf_start
       2: 0000000000000200     0 NOTYPE  LOCAL  DEFAULT   18 __irf_end
       3: 0000000000000000     0 SECTION LOCAL  DEFAULT   17 .text
       4: 0000000000000000     0 SECTION LOCAL  DEFAULT   18 .init.ramfs

This causes klp-build warnings like:

  vmlinux.o: warning: objtool: no correlation: __irf_start
  vmlinux.o: warning: objtool: no correlation: __irf_end

The problem is that Clang LTO is stripping the initramfs_data.o FILE
symbol, causing those two symbols to be orphaned and not noticed by
klp-diff's correlation logic.  Add a loop to correlate any symbols found
before the first FILE symbol.

Fixes: dd590d4d57 ("objtool/klp: Introduce klp diff subcommand for diffing object files")
Reported-by: Song Liu <song@kernel.org>
Acked-by: Song Liu <song@kernel.org>
Link: https://patch.msgid.link/e21ec1141fc749b5f538d7329b531c1ab63a6d1a.1770055235.git.jpoimboe@kernel.org
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
This commit is contained in:
Josh Poimboeuf 2026-02-02 10:01:08 -08:00
parent b525fcaf0a
commit 18328546dd
1 changed files with 34 additions and 5 deletions
Download patch file Download diff file Expand all files Collapse all files

39
tools/objtool/klp-diff.c
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@ -364,11 +364,40 @@ static int correlate_symbols(struct elfs *e)
struct symbol *file1_sym, *file2_sym;
struct symbol *sym1, *sym2;
/* Correlate locals */
for (file1_sym = first_file_symbol(e->orig),
file2_sym = first_file_symbol(e->patched); ;
file1_sym = next_file_symbol(e->orig, file1_sym),
file2_sym = next_file_symbol(e->patched, file2_sym)) {
file1_sym = first_file_symbol(e->orig);
file2_sym = first_file_symbol(e->patched);
/*
* Correlate any locals before the first FILE symbol. This has been
* seen when LTO inexplicably strips the initramfs_data.o FILE symbol
* due to the file only containing data and no code.
*/
for_each_sym(e->orig, sym1) {
if (sym1 == file1_sym || !is_local_sym(sym1))
break;
if (dont_correlate(sym1))
continue;
for_each_sym(e->patched, sym2) {
if (sym2 == file2_sym || !is_local_sym(sym2))
break;
if (sym2->twin || dont_correlate(sym2))
continue;
if (strcmp(sym1->demangled_name, sym2->demangled_name))
continue;
sym1->twin = sym2;
sym2->twin = sym1;
break;
}
}
/* Correlate locals after the first FILE symbol */
for (; ; file1_sym = next_file_symbol(e->orig, file1_sym),
file2_sym = next_file_symbol(e->patched, file2_sym)) {
if (!file1_sym && file2_sym) {
ERROR("FILE symbol mismatch: NULL != %s", file2_sym->name);