On Wed, Jan 06, 2021 at 09:33:20PM -0600, Josh Poimboeuf wrote: > 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.
Right, overlapping things needs a different data structure, could be done though, but like you say, moar work. > Reported-by: Arnd Bergmann <a...@kernel.org> > Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com> Acked-by: Peter Zijlstra (Intel) <pet...@infradead.org> > --- > tools/objtool/elf.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c > index be89c741ba9a..ccee8fc331f0 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 real function, confusing the sorting. > + */ > + if (!sym->len) > + rb_erase(&sym->node, &sym->sec->symbol_tree); > } > > if (stats) > -- > 2.29.2 >
