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target/s390x: Fix determination of overflow condition code after subtraction

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Reported by Paul Eggert in
https://lists.gnu.org/archive/html/bug-gnulib/2021-09/msg00050.html

This program currently prints different results when run with TCG instead
of running on real s390x hardware:

 #include <stdio.h>

 int overflow_32 (int x, int y)
 {
   int sum;
   return __builtin_sub_overflow (x, y, &sum);
 }

 int overflow_64 (long long x, long long y)
 {
   long sum;
   return __builtin_sub_overflow (x, y, &sum);
 }

 int a1 = 0;
 int b1 = -2147483648;
 long long a2 = 0L;
 long long b2 = -9223372036854775808L;

 int main ()
 {
   {
     int a = a1;
     int b = b1;
     printf ("a = 0x%x, b = 0x%x\n", a, b);
     printf ("no_overflow = %d\n", ! overflow_32 (a, b));
   }
   {
     long long a = a2;
     long long b = b2;
     printf ("a = 0x%llx, b = 0x%llx\n", a, b);
     printf ("no_overflow = %d\n", ! overflow_64 (a, b));
   }
 }

Signed-off-by: Bruno Haible <bruno@clisp.org>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/618
Message-Id: <20220323162621.139313-3-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
This commit is contained in:
Bruno Haible 2022-03-23 17:26:21 +01:00 committed by Thomas Huth
parent 5a2e67a691
commit fc6e0d0f2d
1 changed files with 2 additions and 2 deletions
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4
target/s390x/tcg/cc_helper.c
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@ -151,7 +151,7 @@ static uint32_t cc_calc_add_64(int64_t a1, int64_t a2, int64_t ar)
static uint32_t cc_calc_sub_64(int64_t a1, int64_t a2, int64_t ar)
{
if ((a1 > 0 && a2 < 0 && ar < 0) || (a1 < 0 && a2 > 0 && ar > 0)) {
if ((a1 >= 0 && a2 < 0 && ar < 0) || (a1 < 0 && a2 > 0 && ar > 0)) {
return 3; /* overflow */
} else {
if (ar < 0) {
@ -211,7 +211,7 @@ static uint32_t cc_calc_add_32(int32_t a1, int32_t a2, int32_t ar)
static uint32_t cc_calc_sub_32(int32_t a1, int32_t a2, int32_t ar)
{
if ((a1 > 0 && a2 < 0 && ar < 0) || (a1 < 0 && a2 > 0 && ar > 0)) {
if ((a1 >= 0 && a2 < 0 && ar < 0) || (a1 < 0 && a2 > 0 && ar > 0)) {
return 3; /* overflow */
} else {
if (ar < 0) {