From: Josh Poimboeuf jpoimboe@redhat.com
commit e81e0724432542af8d8c702c31e9d82f57b1ff31 upstream.
When compiling the kernel with AS=clang, objtool produces a lot of warnings:
warning: objtool: missing symbol for section .text warning: objtool: missing symbol for section .init.text warning: objtool: missing symbol for section .ref.text
It then fails to generate the ORC table.
The problem is that objtool assumes text section symbols always exist. But the Clang assembler is aggressive about removing them.
When generating relocations for the ORC table, objtool always tries to reference instructions by their section symbol offset. If the section symbol doesn't exist, it bails.
Do a fallback: when a section symbol isn't available, reference a function symbol instead.
Reported-by: Dmitry Golovin dima@golovin.in Signed-off-by: Josh Poimboeuf jpoimboe@redhat.com Signed-off-by: Borislav Petkov bp@suse.de Tested-by: Nathan Chancellor natechancellor@gmail.com Reviewed-by: Miroslav Benes mbenes@suse.cz Acked-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://github.com/ClangBuiltLinux/linux/issues/669 Link: https://lkml.kernel.org/r/9a9cae7fcf628843aabe5a086b1a3c5bf50f42e8.158576102... Cc: Nick Desaulniers ndesaulniers@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- tools/objtool/orc_gen.c | 33 ++++++++++++++++++++++++++------- 1 file changed, 26 insertions(+), 7 deletions(-)
--- a/tools/objtool/orc_gen.c +++ b/tools/objtool/orc_gen.c @@ -100,11 +100,6 @@ static int create_orc_entry(struct secti struct orc_entry *orc; struct rela *rela;
- if (!insn_sec->sym) { - WARN("missing symbol for section %s", insn_sec->name); - return -1; - } - /* populate ORC data */ orc = (struct orc_entry *)u_sec->data->d_buf + idx; memcpy(orc, o, sizeof(*orc)); @@ -117,8 +112,32 @@ static int create_orc_entry(struct secti } memset(rela, 0, sizeof(*rela));
- rela->sym = insn_sec->sym; - rela->addend = insn_off; + if (insn_sec->sym) { + rela->sym = insn_sec->sym; + rela->addend = insn_off; + } else { + /* + * The Clang assembler doesn't produce section symbols, so we + * have to reference the function symbol instead: + */ + rela->sym = find_symbol_containing(insn_sec, insn_off); + if (!rela->sym) { + /* + * Hack alert. This happens when we need to reference + * the NOP pad insn immediately after the function. + */ + rela->sym = find_symbol_containing(insn_sec, + insn_off - 1); + } + if (!rela->sym) { + WARN("missing symbol for insn at offset 0x%lx\n", + insn_off); + return -1; + } + + rela->addend = insn_off - rela->sym->offset; + } + rela->type = R_X86_64_PC32; rela->offset = idx * sizeof(int);