From a2e38dffcd93541914aba52b30c6a52acca35201 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Tue, 5 Jan 2021 18:04:20 -0600 Subject: [PATCH 1/3] 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) From 655cf86548a3938538642a6df27dd359e13c86bd Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Thu, 14 Jan 2021 16:32:42 -0600 Subject: [PATCH 2/3] objtool: Don't fail the kernel build on fatal errors This is basically a revert of commit 644592d32837 ("objtool: Fail the kernel build on fatal errors"). That change turned out to be more trouble than it's worth. Failing the build is an extreme measure which sometimes gets too much attention and blocks CI build testing. These fatal-type warnings aren't yet as rare as we'd hope, due to the ever-increasing matrix of supported toolchains/plugins and their fast-changing nature as of late. Also, there are more people (and bots) looking for objtool warnings than ever before, so even non-fatal warnings aren't likely to be ignored for long. Suggested-by: Nick Desaulniers Reviewed-by: Miroslav Benes Reviewed-by: Nick Desaulniers Reviewed-by: Kamalesh Babulal Signed-off-by: Josh Poimboeuf --- tools/objtool/check.c | 14 +++++--------- 1 file changed, 5 insertions(+), 9 deletions(-) diff --git a/tools/objtool/check.c b/tools/objtool/check.c index 5f8d3eed78a1..4bd30315eb62 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -2928,14 +2928,10 @@ int check(struct objtool_file *file) warnings += ret; out: - if (ret < 0) { - /* - * Fatal error. The binary is corrupt or otherwise broken in - * some way, or objtool itself is broken. Fail the kernel - * build. - */ - return ret; - } - + /* + * For now, don't fail the kernel build on fatal warnings. These + * errors are still fairly common due to the growing matrix of + * supported toolchains and their recent pace of change. + */ return 0; } From 1d489151e9f9d1647110277ff77282fe4d96d09b Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Thu, 14 Jan 2021 16:14:01 -0600 Subject: [PATCH 3/3] objtool: Don't fail on missing symbol table Thanks to a recent binutils change which doesn't generate unused symbols, it's now possible for thunk_64.o be completely empty without CONFIG_PREEMPTION: no text, no data, no symbols. We could edit the Makefile to only build that file when CONFIG_PREEMPTION is enabled, but that will likely create confusion if/when the thunks end up getting used by some other code again. Just ignore it and move on. Reported-by: Nathan Chancellor Reviewed-by: Nathan Chancellor Reviewed-by: Miroslav Benes Tested-by: Nathan Chancellor Link: https://github.com/ClangBuiltLinux/linux/issues/1254 Signed-off-by: Josh Poimboeuf --- tools/objtool/elf.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c index f9682db33cca..d8421e1d06be 100644 --- a/tools/objtool/elf.c +++ b/tools/objtool/elf.c @@ -380,8 +380,11 @@ static int read_symbols(struct elf *elf) symtab = find_section_by_name(elf, ".symtab"); if (!symtab) { - WARN("missing symbol table"); - return -1; + /* + * A missing symbol table is actually possible if it's an empty + * .o file. This can happen for thunk_64.o. + */ + return 0; } symtab_shndx = find_section_by_name(elf, ".symtab_shndx");