From c8a5496bc747650a538b291ad3feee94747ff539 Mon Sep 17 00:00:00 2001 From: Josh Poimboeuf Date: Wed, 1 Apr 2020 13:23:27 -0500 Subject: [PATCH] objtool: Support Clang non-section symbols in ORC generation 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 Signed-off-by: Josh Poimboeuf Signed-off-by: Borislav Petkov Tested-by: Nathan Chancellor Reviewed-by: Miroslav Benes Acked-by: Peter Zijlstra (Intel) Link: https://github.com/ClangBuiltLinux/linux/issues/669 Link: https://lkml.kernel.org/r/9a9cae7fcf628843aabe5a086b1a3c5bf50f42e8.1585761021.git.jpoimboe@redhat.com Cc: Nick Desaulniers Signed-off-by: Greg Kroah-Hartman --- tools/objtool/orc_gen.c | 33 ++++++++++++++++++++++++++------- 1 file changed, 26 insertions(+), 7 deletions(-) diff --git a/tools/objtool/orc_gen.c b/tools/objtool/orc_gen.c index 27a4112848c2b..e8c34b0a8b00c 100644 --- a/tools/objtool/orc_gen.c +++ b/tools/objtool/orc_gen.c @@ -88,11 +88,6 @@ static int create_orc_entry(struct section *u_sec, struct section *ip_relasec, 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)); @@ -105,8 +100,32 @@ static int create_orc_entry(struct section *u_sec, struct section *ip_relasec, } 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);