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objtool: Support Clang non-section symbols in ORC generation 

BugLink: https://bugs.launchpad.net/bugs/1904445

commit e81e072443 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/9a9cae7fcf628843aabe5a086b1a3c5bf50f42e8.1585761021.git.jpoimboe@redhat.com
Cc: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: William Breathitt Gray <william.gray@canonical.com>
This commit is contained in:
Josh Poimboeuf 2020-04-01 13:23:27 -05:00 committed by Stefan Bader
parent 39b65ce394
commit 553fe231cd
1 changed files with 26 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

33
tools/objtool/orc_gen.c
View File

@ -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);