On Thu, Jan 18, 2018 at 11:09:31AM -0800, Guenter Roeck wrote: > Hi folks, > > On Thu, Jan 11, 2018 at 09:46:24PM +0000, Woodhouse, David wrote: > > Getting objtool to understand retpolines is going to be a bit of a > > challenge. For now, take advantage of the fact that retpolines are > > patched in with alternatives. Just read the original (sane) > > non-alternative instruction, and ignore the patched-in retpoline. > > > > This allows objtool to understand the control flow *around* the > > retpoline, even if it can't yet follow what's inside. This means the > > ORC unwinder will fail to unwind from inside a retpoline, but will work > > fine otherwise. > > > > Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com> > > Signed-off-by: David Woodhouse <d...@amazon.co.uk> > > --- > > tools/objtool/check.c | 62 > > ++++++++++++++++++++++++++++++++++++++++++++++----- > > tools/objtool/check.h | 2 +- > > 2 files changed, 57 insertions(+), 7 deletions(-) > > > > diff --git a/tools/objtool/check.c b/tools/objtool/check.c > > index de053fb..f40d46e 100644 > > --- a/tools/objtool/check.c > > +++ b/tools/objtool/check.c > > @@ -428,6 +428,40 @@ static void add_ignores(struct objtool_file *file) > > } > > > > /* > > + * FIXME: For now, just ignore any alternatives which add retpolines. > > This is > > + * a temporary hack, as it doesn't allow ORC to unwind from inside a > > retpoline. > > + * But it at least allows objtool to understand the control flow *around* > > the > > + * retpoline. > > + */ > > +static int add_nospec_ignores(struct objtool_file *file) > > +{ > > + struct section *sec; > > + struct rela *rela; > > + struct instruction *insn; > > + > > + sec = find_section_by_name(file->elf, ".rela.discard.nospec"); > > + if (!sec) > > + return 0; > > + > > + list_for_each_entry(rela, &sec->rela_list, list) { > > + if (rela->sym->type != STT_SECTION) { > > + WARN("unexpected relocation symbol type in %s", > > sec->name); > > + return -1; > > + } > > + > > + insn = find_insn(file, rela->sym->sec, rela->addend); > > + if (!insn) { > > + WARN("bad .discard.nospec entry"); > > + return -1; > > + } > > + > > + insn->ignore_alts = true; > > + } > > + > > + return 0; > > +} > > + > > +/* > > * Find the destination instructions for all jumps. > > */ > > static int add_jump_destinations(struct objtool_file *file) > > @@ -509,11 +543,18 @@ static int add_call_destinations(struct objtool_file > > *file) > > dest_off = insn->offset + insn->len + insn->immediate; > > insn->call_dest = find_symbol_by_offset(insn->sec, > > dest_off); > > + /* > > + * FIXME: Thanks to retpolines, it's now considered > > + * normal for a function to call within itself. So > > + * disable this warning for now. > > + */ > > +#if 0 > > if (!insn->call_dest) { > > WARN_FUNC("can't find call dest symbol at > > offset 0x%lx", > > insn->sec, insn->offset, dest_off); > > return -1; > > } > > +#endif > > This crashes for me in is_fentry_call(). > > Program received signal SIGSEGV, Segmentation fault. > is_fentry_call (insn=<optimized out>, insn=<optimized out>) at check.c:1113 > 1113 if (insn->type == INSN_CALL && > (gdb) info stack > #0 is_fentry_call (insn=<optimized out>, insn=<optimized out>) at > check.c:1113 > #1 validate_branch (file=0x7ffffff7e440, first=0x7ffffff7e128, state=...) at > check.c:1747 > #2 0x0000000000404bd3 in validate_branch (file=0x7ffffff7e440, > first=0x7ffffff7e128, state=...) at check.c:1770 > #3 0x0000000000406783 in validate_functions (file=<optimized out>) at > check.c:1933 > #4 check (_objname=0x6bb9d0 "", _no_fp=40, no_unreachable=4, orc=false) at > check.c:2006 > #5 0x00000000004021c1 in handle_internal_command (argv=0x7fffffffe5c0, > argc=4) at objtool.c:108 > #6 main (argc=4, argv=0x7fffffffe5c0) at objtool.c:131 > > This is not entirely surprising, since insn->call_dest is NULL and > is_fentry_call() doesn't expect that. > > How is this supposed to work ? What am I missing ?
Not sure, does your gcc have retpolines? Give me your .o file and I can diagnose it. I intended to have an error msg instead of a seg fault for this situation, just haven't had a chance to improve that yet in the midst of all the hoopla. -- Josh