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Date: Tue, 18 Feb 2020 10:13:54 -0800
From: Nick Desaulniers <ndesaulniers@...gle.com>
To: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
LKML <linux-kernel@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 2/2] objtool: Improve call destination function detection
On Mon, Feb 17, 2020 at 7:42 PM Josh Poimboeuf <jpoimboe@...hat.com> wrote:
>
> A recent clang change, combined with a binutils bug, can trigger a
> situation where a ".Lprintk$local" STT_NOTYPE symbol gets created at the
> same offset as the "printk" STT_FUNC symbol. This confuses objtool:
>
> kernel/printk/printk.o: warning: objtool: ignore_loglevel_setup()+0x10: can't find call dest symbol at .text+0xc67
>
> Improve the call destination detection by looking specifically for an
> STT_FUNC symbol.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/872
> Link: https://sourceware.org/bugzilla/show_bug.cgi?id=25551
> Reported-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
Thanks Josh.
Tested-by: Nick Desaulniers <ndesaulniers@...gle.com>
Tested defconfig and allyesconfig builds with the series.
> ---
> tools/objtool/check.c | 27 ++++++++++++++++++---------
> tools/objtool/elf.c | 14 ++++++++++++--
> tools/objtool/elf.h | 1 +
> 3 files changed, 31 insertions(+), 11 deletions(-)
>
> diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> index e7227649bac7..da0767128f61 100644
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -415,8 +415,8 @@ static void add_ignores(struct objtool_file *file)
> break;
>
> case STT_SECTION:
> - func = find_symbol_by_offset(rela->sym->sec, rela->addend);
> - if (!func || func->type != STT_FUNC)
> + func = find_func_by_offset(rela->sym->sec, rela->addend);
> + if (!func)
> continue;
> break;
>
> @@ -679,10 +679,14 @@ static int add_call_destinations(struct objtool_file *file)
> insn->len);
> if (!rela) {
> dest_off = insn->offset + insn->len + insn->immediate;
> - insn->call_dest = find_symbol_by_offset(insn->sec,
> - dest_off);
> + insn->call_dest = find_func_by_offset(insn->sec, dest_off);
> + if (!insn->call_dest)
> + insn->call_dest = find_symbol_by_offset(insn->sec, dest_off);
>
> - if (!insn->call_dest && !insn->ignore) {
> + if (insn->ignore)
> + continue;
> +
> + if (!insn->call_dest) {
> WARN_FUNC("unsupported intra-function call",
> insn->sec, insn->offset);
> if (retpoline)
> @@ -690,11 +694,16 @@ static int add_call_destinations(struct objtool_file *file)
> return -1;
> }
>
> + if (insn->func && insn->call_dest->type != STT_FUNC) {
> + WARN_FUNC("unsupported call to non-function",
> + insn->sec, insn->offset);
> + return -1;
> + }
> +
> } else if (rela->sym->type == STT_SECTION) {
> - insn->call_dest = find_symbol_by_offset(rela->sym->sec,
> - rela->addend+4);
> - if (!insn->call_dest ||
> - insn->call_dest->type != STT_FUNC) {
> + insn->call_dest = find_func_by_offset(rela->sym->sec,
> + rela->addend+4);
> + if (!insn->call_dest) {
> WARN_FUNC("can't find call dest symbol at %s+0x%x",
> insn->sec, insn->offset,
> rela->sym->sec->name,
> diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
> index edba4745f25a..cc4601c879ce 100644
> --- a/tools/objtool/elf.c
> +++ b/tools/objtool/elf.c
> @@ -62,8 +62,18 @@ struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset)
> struct symbol *sym;
>
> list_for_each_entry(sym, &sec->symbol_list, list)
> - if (sym->type != STT_SECTION &&
> - sym->offset == offset)
> + if (sym->type != STT_SECTION && sym->offset == offset)
> + return sym;
> +
> + return NULL;
> +}
> +
> +struct symbol *find_func_by_offset(struct section *sec, unsigned long offset)
> +{
> + struct symbol *sym;
> +
> + list_for_each_entry(sym, &sec->symbol_list, list)
> + if (sym->type == STT_FUNC && sym->offset == offset)
> return sym;
>
> return NULL;
> diff --git a/tools/objtool/elf.h b/tools/objtool/elf.h
> index 44150204db4d..a1963259b930 100644
> --- a/tools/objtool/elf.h
> +++ b/tools/objtool/elf.h
> @@ -77,6 +77,7 @@ struct elf {
>
> struct elf *elf_read(const char *name, int flags);
> struct section *find_section_by_name(struct elf *elf, const char *name);
> +struct symbol *find_func_by_offset(struct section *sec, unsigned long offset);
> struct symbol *find_symbol_by_offset(struct section *sec, unsigned long offset);
> struct symbol *find_symbol_by_name(struct elf *elf, const char *name);
> struct symbol *find_symbol_containing(struct section *sec, unsigned long offset);
> --
> 2.21.1
>
--
Thanks,
~Nick Desaulniers
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