Messages in this thread | | | Date | Thu, 30 Sep 2021 10:32:07 -0700 | From | Nathan Chancellor <> | Subject | Re: [PATCH] objtool: Teach get_alt_entry() about more relocation types |
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On Thu, Sep 30, 2021 at 12:43:10PM +0200, Peter Zijlstra wrote: > > Occasionally objtool encounters symbol (as opposed to section) > relocations in .altinstructions. Typically they are the alternatives > written by elf_add_alternative() as encountered on a noinstr > validation run on vmlinux after having already ran objtool on the > individual .o files. > > Basically this is the counterpart of commit 44f6a7c0755d ("objtool: > Fix seg fault with Clang non-section symbols"), because when these new > assemblers (binutils now also does this) strip the section symbols, > elf_add_reloc_to_insn() is forced to emit symbol based relocations. > > As such, teach get_alt_entry() about different relocation types. > > Fixes: 9bc0bb50727c ("objtool/x86: Rewrite retpoline thunk calls") > Reported-by: Stephen Rothwell <sfr@canb.auug.org.au> > Reported-by: Borislav Petkov <bp@alien8.de> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
This resolves the instance of the warning that I see with clang-12:
Tested-by: Nathan Chancellor <nathan@kernel.org>
> --- > tools/objtool/special.c | 32 +++++++++++++++++++++++++------- > 1 file changed, 25 insertions(+), 7 deletions(-) > > --- a/tools/objtool/special.c > +++ b/tools/objtool/special.c > @@ -58,6 +58,24 @@ void __weak arch_handle_alternative(unsi > { > } > > +static bool reloc2sec_off(struct reloc *reloc, struct section **sec, unsigned long *off) > +{ > + switch (reloc->sym->type) { > + case STT_FUNC: > + *sec = reloc->sym->sec; > + *off = reloc->sym->offset + reloc->addend; > + return true; > + > + case STT_SECTION: > + *sec = reloc->sym->sec; > + *off = reloc->addend; > + return true; > + > + default: > + return false; > + } > +} > + > static int get_alt_entry(struct elf *elf, struct special_entry *entry, > struct section *sec, int idx, > struct special_alt *alt) > @@ -91,15 +109,12 @@ static int get_alt_entry(struct elf *elf > WARN_FUNC("can't find orig reloc", sec, offset + entry->orig); > return -1; > } > - if (orig_reloc->sym->type != STT_SECTION) { > - WARN_FUNC("don't know how to handle non-section reloc symbol %s", > + if (!reloc2sec_off(orig_reloc, &alt->orig_sec, &alt->orig_off)) { > + WARN_FUNC("don't know how to handle reloc symbol type: %s", > sec, offset + entry->orig, orig_reloc->sym->name); > return -1; > } > > - alt->orig_sec = orig_reloc->sym->sec; > - alt->orig_off = orig_reloc->addend; > - > if (!entry->group || alt->new_len) { > new_reloc = find_reloc_by_dest(elf, sec, offset + entry->new); > if (!new_reloc) { > @@ -116,8 +131,11 @@ static int get_alt_entry(struct elf *elf > if (arch_is_retpoline(new_reloc->sym)) > return 1; > > - alt->new_sec = new_reloc->sym->sec; > - alt->new_off = (unsigned int)new_reloc->addend; > + if (!reloc2sec_off(new_reloc, &alt->new_sec, &alt->new_off)) { > + WARN_FUNC("don't know how to handle reloc symbol type: %s", > + sec, offset + entry->new, new_reloc->sym->name); > + return -1; > + } > > /* _ASM_EXTABLE_EX hack */ > if (alt->new_off >= 0x7ffffff0) >
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