From a2e38dffcd93541914aba52b30c6a52acca35201 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Tue, 5 Jan 2021 18:04:20 -0600 Subject: [PATCH] objtool: Don't add empty symbols to the rbtree 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 Acked-by: Peter Zijlstra (Intel) Signed-off-by: Josh Poimboeuf --- tools/objtool/elf.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c index be89c741ba9a..f9682db33cca 100644 --- a/tools/objtool/elf.c +++ b/tools/objtool/elf.c @@ -448,6 +448,13 @@ 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) -- 2.39.2