[Qemu-devel] [CFT] target-ppc: Fix narrow-mode add/sub carry output

[Richard Henderson <rth@twiddle.net>]

Broken in b5a73f8d8a57e940f9bbeb399a9e47897522ee9a, the carry itself was
fixed in 79482e5ab38a05ca8869040b0d8b8f451f16ff62.  But we still need to
produce the full 64-bit addition.

Cc: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Richard Henderson <rth@twiddle.net>
---
Aurelien, you reported this bug, but I'm unable to reproduce it at the
moment.  That test program you sent along is broken, attempting to run
insns in pages without the execute bit set.  I don't have time to fix
that today.

But per IRC, I think we know what the problem is.  And at least this
runs the linux-user-0.3 ppc binaries properly.  Hopefully it'll solve
the real problem with your guest openssl.


r~
---
 target-ppc/translate.c | 30 ++++++++++++++++++++----------
 1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/target-ppc/translate.c b/target-ppc/translate.c
index 5e741d1..1feadca 100644
--- a/target-ppc/translate.c
+++ b/target-ppc/translate.c
@@ -775,15 +775,19 @@ static inline void gen_op_arith_add(DisasContext *ctx, TCGv ret, TCGv arg1,
 
     if (compute_ca) {
         if (NARROW_MODE(ctx)) {
+            /* Caution: a non-obvious corner case of the spec is that we
+               must produce the *entire* 64-bit addition, but produce the
+               carry into bit 32.  */
             TCGv t1 = tcg_temp_new();
-            tcg_gen_ext32u_tl(t1, arg2);
-            tcg_gen_ext32u_tl(t0, arg1);
-            tcg_gen_add_tl(t0, t0, t1);
-            tcg_temp_free(t1);
+            tcg_gen_xor_tl(t1, arg1, arg2);        /* add without carry */
+            tcg_gen_add_tl(t0, arg1, arg2);
             if (add_ca) {
                 tcg_gen_add_tl(t0, t0, cpu_ca);
             }
-            tcg_gen_shri_tl(cpu_ca, t0, 32);
+            tcg_gen_xor_tl(cpu_ca, t0, t1);        /* bits changed w/ carry */
+            tcg_temp_free(t1);
+            tcg_gen_shri_tl(cpu_ca, cpu_ca, 32);   /* extract bit 32 */
+            tcg_gen_andi_tl(cpu_ca, cpu_ca, 1);
         } else {
             TCGv zero = tcg_const_tl(0);
             if (add_ca) {
@@ -1129,17 +1133,23 @@ static inline void gen_op_arith_subf(DisasContext *ctx, TCGv ret, TCGv arg1,
     if (compute_ca) {
         /* dest = ~arg1 + arg2 [+ ca].  */
         if (NARROW_MODE(ctx)) {
+            /* Caution: a non-obvious corner case of the spec is that we
+               must produce the *entire* 64-bit addition, but produce the
+               carry into bit 32.  */
             TCGv inv1 = tcg_temp_new();
+            TCGv t1 = tcg_temp_new();
             tcg_gen_not_tl(inv1, arg1);
-            tcg_gen_ext32u_tl(t0, arg2);
-            tcg_gen_ext32u_tl(inv1, inv1);
             if (add_ca) {
-                tcg_gen_add_tl(t0, t0, cpu_ca);
+                tcg_gen_add_tl(t0, arg2, cpu_ca);
             } else {
-                tcg_gen_addi_tl(t0, t0, 1);
+                tcg_gen_addi_tl(t0, arg2, 1);
             }
+            tcg_gen_xor_tl(t1, arg2, inv1);         /* add without carry */
             tcg_gen_add_tl(t0, t0, inv1);
-            tcg_gen_shri_tl(cpu_ca, t0, 32);
+            tcg_gen_xor_tl(cpu_ca, t0, t1);         /* bits changes w/ carry */
+            tcg_temp_free(t1);
+            tcg_gen_shri_tl(cpu_ca, cpu_ca, 32);    /* extract bit 32 */
+            tcg_gen_andi_tl(cpu_ca, cpu_ca, 1);
         } else if (add_ca) {
             TCGv zero, inv1 = tcg_temp_new();
             tcg_gen_not_tl(inv1, arg1);
-- 
1.8.1.4