objtool: Teach get_alt_entry() about more relocation types

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>
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

diff --git a/tools/objtool/special.c b/tools/objtool/special.c
index bc925cf..f58ecc5 100644 (file)
--- a/tools/objtool/special.c
+++ b/tools/objtool/special.c
@@ -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)