From: Josh Poimboeuf jpoimboe@redhat.com
[ Upstream commit a2e38dffcd93541914aba52b30c6a52acca35201 ]
Building with the Clang assembler shows the following warning:
arch/x86/kernel/ftrace_64.o: warning: objtool: missing symbol for insn at offset 0x16
The Clang assembler strips section symbols. That ends up giving objtool's find_func_containing() much more test coverage than normal. Turns out, find_func_containing() doesn't work so well for overlapping symbols:
2: 000000000000000e 0 NOTYPE LOCAL DEFAULT 2 fgraph_trace 3: 000000000000000f 0 NOTYPE LOCAL DEFAULT 2 trace 4: 0000000000000000 165 FUNC GLOBAL DEFAULT 2 __fentry__ 5: 000000000000000e 0 NOTYPE GLOBAL DEFAULT 2 ftrace_stub
The zero-length NOTYPE symbols are inside __fentry__(), confusing the rbtree search for any __fentry__() offset coming after a NOTYPE.
Try to avoid this problem by not adding zero-length symbols to the rbtree. They're rare and aren't needed in the rbtree anyway.
One caveat, this actually might not end up being the right fix. Non-empty overlapping symbols, if they exist, could have the same problem. But that would need bigger changes, let's see if we can get away with the easy fix for now.
Reported-by: Arnd Bergmann arnd@kernel.org Acked-by: Peter Zijlstra (Intel) peterz@infradead.org Signed-off-by: Josh Poimboeuf jpoimboe@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- tools/objtool/elf.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c index 9452cfb01ef19..f4f3e8d995930 100644 --- a/tools/objtool/elf.c +++ b/tools/objtool/elf.c @@ -425,6 +425,13 @@ static int read_symbols(struct elf *elf) list_add(&sym->list, entry); elf_hash_add(elf->symbol_hash, &sym->hash, sym->idx); elf_hash_add(elf->symbol_name_hash, &sym->name_hash, str_hash(sym->name)); + + /* + * Don't store empty STT_NOTYPE symbols in the rbtree. They + * can exist within a function, confusing the sorting. + */ + if (!sym->len) + rb_erase(&sym->node, &sym->sec->symbol_tree); }
if (stats)