Messages in this thread | | | Date | Fri, 3 Apr 2020 10:58:20 +0200 (CEST) | From | Miroslav Benes <> | Subject | Re: [PATCH 3/5] objtool: Support Clang non-section symbols in ORC generation |
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On Wed, 1 Apr 2020, Josh Poimboeuf wrote:
> 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. > > Link: https://github.com/ClangBuiltLinux/linux/issues/669 > Cc: Nick Desaulniers <ndesaulniers@google.com> > Reported-by: Dmitry Golovin <dima@golovin.in> > Tested-by: Nathan Chancellor <natechancellor@gmail.com> > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> > --- > 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 41e4a2754da4..4c0dabd28000 100644 > --- a/tools/objtool/orc_gen.c > +++ b/tools/objtool/orc_gen.c > @@ -88,11 +88,6 @@ static int create_orc_entry(struct elf *elf, struct section *u_sec, 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)); > @@ -105,8 +100,32 @@ static int create_orc_entry(struct elf *elf, struct section *u_sec, 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); > + }
I suppose there is always just one NOP pad insn, right? Anyway, it would be better to get rid of it as you proposed.
> + 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); > rela->sec = ip_relasec;
Miroslav
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