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objtool: Teach get_alt_entry() about more relocation types

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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 44f6a7c075 ("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: 9bc0bb5072 ("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>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/YVWUvknIEVNkPvnP@hirez.programming.kicks-ass.net
This commit is contained in:
Peter Zijlstra 2021-09-30 12:43:10 +02:00
parent e4e737bb5c
commit 24ff652573
1 changed files with 25 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

32
tools/objtool/special.c
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@ -58,6 +58,24 @@ void __weak arch_handle_alternative(unsigned short feature, struct special_alt *
{
}
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, struct special_entry *entry,
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, struct special_entry *entry,
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)