6l: Relocate CMOV* instructions

The linker avoids a GOT indirection by turning a MOV into
a LEA, but with x86-64 GCC has started emitting CMOV*
instructions which break the existing logic.

This will generate errors such as:

  unexpected GOT reloc for non-dynamic symbol luaO_nilobject_

The CMOV* instructions may be emitted with normal code like:

  if (o >= L->top) return cast(TValue *, luaO_nilobject);
  else return o;

Which gets compiled into (relocation offset at 1b):

  13: 48 3b 47 10             cmp    0x10(%rdi),%rax
  17: 48 0f 43 05 00 00 00    cmovae 0x0(%rip),%rax
  1e: 00

This change will allow the indirection through the GOT to
avoid the problem in those cases.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/4071044

diff --git a/src/cmd/6l/asm.c b/src/cmd/6l/asm.c
index 2119395b38b72ec86b781e1ac5ede35f6d7e63cc..2e401db9130a786837152303abd95ecec4e7ea77 100644 (file)
--- a/src/cmd/6l/asm.c
+++ b/src/cmd/6l/asm.c
@@ -206,15 +206,15 @@ adddynrel(Sym *s, Reloc *r)
        case 256 + R_X86_64_GOTPCREL:
                if(targ->dynimpname == nil || targ->dynexport) {
                        // have symbol
-                       // turn MOVQ of GOT entry into LEAQ of symbol itself
-                       if(r->off < 2 || s->p[r->off-2] != 0x8b) {
-                               diag("unexpected GOT_LOAD reloc for non-dynamic symbol %s", targ->name);
+                       if(r->off >= 2 && s->p[r->off-2] == 0x8b) {
+                               // turn MOVQ of GOT entry into LEAQ of symbol itself
+                               s->p[r->off-2] = 0x8d;
+                               r->type = D_PCREL;
+                               r->add += 4;
                                return;
                        }
-                       s->p[r->off-2] = 0x8d;
-                       r->type = D_PCREL;
-                       r->add += 4;
-                       return;
+                       // unknown instruction (CMOV* maybe), use GOT
+                       targ->dynimpname = targ->name;
                }
                addgotsym(targ);
                r->type = D_PCREL;