objtool: Allow !PC relative relocations

Objtool doesn't currently much like per-cpu usage in alternatives:

arch/x86/entry/entry_64.o: warning: objtool: .altinstr_replacement+0xf: unsupported relocation in alternatives section
  f:   65 c7 04 25 00 00 00 00 00 00 00 80     movl   $0x80000000,%gs:0x0      13: R_X86_64_32S        __x86_call_depth

Since the R_X86_64_32S relocation is location invariant (it's
computation doesn't include P - the address of the location itself),
it can be trivially allowed.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220915111145.806607235@infradead.org

diff --git a/tools/objtool/arch/x86/decode.c b/tools/objtool/arch/x86/decode.c
index 1c253b4..f094383 100644 (file)
--- a/tools/objtool/arch/x86/decode.c
+++ b/tools/objtool/arch/x86/decode.c
@@ -73,6 +73,30 @@ unsigned long arch_jump_destination(struct instruction *insn)
        return insn->offset + insn->len + insn->immediate;
 }
 
+bool arch_pc_relative_reloc(struct reloc *reloc)
+{
+       /*
+        * All relocation types where P (the address of the target)
+        * is included in the computation.
+        */
+       switch (reloc->type) {
+       case R_X86_64_PC8:
+       case R_X86_64_PC16:
+       case R_X86_64_PC32:
+       case R_X86_64_PC64:
+
+       case R_X86_64_PLT32:
+       case R_X86_64_GOTPC32:
+       case R_X86_64_GOTPCREL:
+               return true;
+
+       default:
+               break;
+       }
+
+       return false;
+}
+
 #define ADD_OP(op) \
        if (!(op = calloc(1, sizeof(*op)))) \
                return -1; \

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index 43ec14c..7174bba 100644 (file)
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -1645,7 +1645,7 @@ static int handle_group_alt(struct objtool_file *file,
                 * accordingly.
                 */
                alt_reloc = insn_reloc(file, insn);
-               if (alt_reloc &&
+               if (alt_reloc && arch_pc_relative_reloc(alt_reloc) &&
                    !arch_support_alt_relocation(special_alt, insn, alt_reloc)) {
 
                        WARN_FUNC("unsupported relocation in alternatives section",

diff --git a/tools/objtool/include/objtool/arch.h b/tools/objtool/include/objtool/arch.h
index beb2f3a..fe2ea4b 100644 (file)
--- a/tools/objtool/include/objtool/arch.h
+++ b/tools/objtool/include/objtool/arch.h
@@ -93,4 +93,6 @@ bool arch_is_rethunk(struct symbol *sym);
 
 int arch_rewrite_retpolines(struct objtool_file *file);
 
+bool arch_pc_relative_reloc(struct reloc *reloc);
+
 #endif /* _ARCH_H */