[PULL,061/115] target/i386: fix fxam handling of invalid encodings

Commit Message

Paolo Bonzini June 11, 2020, 7:43 p.m. UTC

From: Joseph Myers <[e-mail]>

The fxam implementation does not check for invalid encodings, instead
treating them like NaN or normal numbers depending on the exponent.
Fix it to check that the high bit of the significand is set before
treating an encoding as NaN or normal, thus resulting in correct
handling (all of C0, C2 and C3 cleared) for invalid encodings.

Signed-off-by: Joseph Myers <[e-mail]>
Message-Id: <[e-mail]>
Signed-off-by: Paolo Bonzini <[e-mail]>
---
 target/i386/fpu_helper.c        |   4 +-
 tests/tcg/i386/test-i386-fxam.c | 143 ++++++++++++++++++++++++++++++++
 2 files changed, 145 insertions(+), 2 deletions(-)
 create mode 100644 tests/tcg/i386/test-i386-fxam.c

Patch

diff --git a/target/i386/fpu_helper.c b/target/i386/fpu_helper.c
index f0b9cb5de8..185493db8e 100644
--- a/target/i386/fpu_helper.c
+++ b/target/i386/fpu_helper.c
@@ -1099,7 +1099,7 @@  void helper_fxam_ST0(CPUX86State *env)
     if (expdif == MAXEXPD) {
         if (MANTD(temp) == 0x8000000000000000ULL) {
             env->fpus |= 0x500; /* Infinity */
-        } else {
+        } else if (MANTD(temp) & 0x8000000000000000ULL) {
             env->fpus |= 0x100; /* NaN */
         }
     } else if (expdif == 0) {
@@ -1108,7 +1108,7 @@  void helper_fxam_ST0(CPUX86State *env)
         } else {
             env->fpus |= 0x4400; /* Denormal */
         }
-    } else {
+    } else if (MANTD(temp) & 0x8000000000000000ULL) {
         env->fpus |= 0x400;
     }
 }
diff --git a/tests/tcg/i386/test-i386-fxam.c b/tests/tcg/i386/test-i386-fxam.c
new file mode 100644
index 0000000000..ddd76ca42d
--- /dev/null
+++ b/tests/tcg/i386/test-i386-fxam.c
@@ -0,0 +1,143 @@ 
+/* Test fxam instruction.  */
+
+#include <stdint.h>
+#include <stdio.h>
+
+union u {
+    struct { uint64_t sig; uint16_t sign_exp; } s;
+    long double ld;
+};
+
+volatile union u ld_pseudo_m16382 = { .s = { UINT64_C(1) << 63, 0 } };
+volatile union u ld_pseudo_nm16382 = { .s = { UINT64_C(1) << 63, 0x8000 } };
+volatile union u ld_invalid_1 = { .s = { 1, 1234 } };
+volatile union u ld_invalid_2 = { .s = { 0, 1234 } };
+volatile union u ld_invalid_3 = { .s = { 0, 0x7fff } };
+volatile union u ld_invalid_4 = { .s = { (UINT64_C(1) << 63) - 1, 0x7fff } };
+volatile union u ld_invalid_n1 = { .s = { 1, 0x8123 } };
+volatile union u ld_invalid_n2 = { .s = { 0, 0x8123 } };
+volatile union u ld_invalid_n3 = { .s = { 0, 0xffff } };
+volatile union u ld_invalid_n4 = { .s = { (UINT64_C(1) << 63) - 1, 0xffff } };
+
+#define C0 (1 << 8)
+#define C1 (1 << 9)
+#define C2 (1 << 10)
+#define C3 (1 << 14)
+#define FLAGS (C0 | C1 | C2 | C3)
+
+int main(void)
+{
+    short sw;
+    int ret = 0;
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (0.0L));
+    if ((sw & FLAGS) != C3) {
+        printf("FAIL: +0\n");
+        ret = 1;
+    }
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (-0.0L));
+    if ((sw & FLAGS) != (C3 | C1)) {
+        printf("FAIL: -0\n");
+        ret = 1;
+    }
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (1.0L));
+    if ((sw & FLAGS) != C2) {
+        printf("FAIL: +normal\n");
+        ret = 1;
+    }
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (-1.0L));
+    if ((sw & FLAGS) != (C2 | C1)) {
+        printf("FAIL: -normal\n");
+        ret = 1;
+    }
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (__builtin_infl()));
+    if ((sw & FLAGS) != (C2 | C0)) {
+        printf("FAIL: +inf\n");
+        ret = 1;
+    }
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (-__builtin_infl()));
+    if ((sw & FLAGS) != (C2 | C1 | C0)) {
+        printf("FAIL: -inf\n");
+        ret = 1;
+    }
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (__builtin_nanl("")));
+    if ((sw & FLAGS) != C0) {
+        printf("FAIL: +nan\n");
+        ret = 1;
+    }
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (-__builtin_nanl("")));
+    if ((sw & FLAGS) != (C1 | C0)) {
+        printf("FAIL: -nan\n");
+        ret = 1;
+    }
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (__builtin_nansl("")));
+    if ((sw & FLAGS) != C0) {
+        printf("FAIL: +snan\n");
+        ret = 1;
+    }
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (-__builtin_nansl("")));
+    if ((sw & FLAGS) != (C1 | C0)) {
+        printf("FAIL: -snan\n");
+        ret = 1;
+    }
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (0x1p-16445L));
+    if ((sw & FLAGS) != (C3 | C2)) {
+        printf("FAIL: +denormal\n");
+        ret = 1;
+    }
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (-0x1p-16445L));
+    if ((sw & FLAGS) != (C3 | C2 | C1)) {
+        printf("FAIL: -denormal\n");
+        ret = 1;
+    }
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (ld_pseudo_m16382.ld));
+    if ((sw & FLAGS) != (C3 | C2)) {
+        printf("FAIL: +pseudo-denormal\n");
+        ret = 1;
+    }
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (ld_pseudo_nm16382.ld));
+    if ((sw & FLAGS) != (C3 | C2 | C1)) {
+        printf("FAIL: -pseudo-denormal\n");
+        ret = 1;
+    }
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (ld_invalid_1.ld));
+    if ((sw & FLAGS) != 0) {
+        printf("FAIL: +invalid 1\n");
+        ret = 1;
+    }
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (ld_invalid_n1.ld));
+    if ((sw & FLAGS) != C1) {
+        printf("FAIL: -invalid 1\n");
+        ret = 1;
+    }
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (ld_invalid_2.ld));
+    if ((sw & FLAGS) != 0) {
+        printf("FAIL: +invalid 2\n");
+        ret = 1;
+    }
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (ld_invalid_n2.ld));
+    if ((sw & FLAGS) != C1) {
+        printf("FAIL: -invalid 2\n");
+        ret = 1;
+    }
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (ld_invalid_3.ld));
+    if ((sw & FLAGS) != 0) {
+        printf("FAIL: +invalid 3\n");
+        ret = 1;
+    }
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (ld_invalid_n3.ld));
+    if ((sw & FLAGS) != C1) {
+        printf("FAIL: -invalid 3\n");
+        ret = 1;
+    }
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (ld_invalid_4.ld));
+    if ((sw & FLAGS) != 0) {
+        printf("FAIL: +invalid 4\n");
+        ret = 1;
+    }
+    __asm__ volatile ("fxam\nfnstsw" : "=a" (sw) : "t" (ld_invalid_n4.ld));
+    if ((sw & FLAGS) != C1) {
+        printf("FAIL: -invalid 4\n");
+        ret = 1;
+    }
+    return ret;
+}