[PATCH 3/3] target/hppa: Fix FPE exceptions

[deller@kernel.org]

From: Helge Deller <deller@gmx.de>

Implement FP exception register #1 (lower 32-bits of 64-bit fr[0]).
A proper implementation is necessary to allow the Linux kernel in
system mode and the qemu linux-user to send proper si_code values
on SIGFPE signal.

Always set the T-bit on taken exception, and merge over- and underflow
in system mode to just set overflow bit to mimic the behaviour I tested
on a physical machine.

The test program below can be used to verify correct behaviour. Note
that behaviour on SIGFPE may vary on different platforms. The program
should always detect the correct signal, but it may or may not be able
to sucessfully continue afterwards.

 #define _GNU_SOURCE
 #include <signal.h>
 #include <stdio.h>
 #include <fenv.h>
 #include <float.h>

 static void fpe_func(int sig, siginfo_t *i, void *v) {
    sigset_t set;
    sigemptyset(&set);
    sigaddset(&set, SIGFPE);
    sigprocmask(SIG_UNBLOCK, &set, NULL);
    printf("GOT signal %d with si_code %ld\n", sig, i->si_code);
 }

 int main(int argc, char *argv[]) {
    struct sigaction action = {
        .sa_sigaction = fpe_func,
        .sa_flags = SA_RESTART|SA_SIGINFO };
    sigaction(SIGFPE, &action, 0);
    feenableexcept(FE_OVERFLOW | FE_UNDERFLOW);
    double x = DBL_MIN;
    return printf("%lf\n", argc > 1
        ? 1.7976931348623158E308*1.7976931348623158E308
        : x / 10);
 }

Signed-off-by: Helge Deller <deller@gmx.de>
---
 target/hppa/fpu_helper.c | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/target/hppa/fpu_helper.c b/target/hppa/fpu_helper.c
index a62d9d3083..294ce0a970 100644
--- a/target/hppa/fpu_helper.c
+++ b/target/hppa/fpu_helper.c
@@ -95,7 +95,8 @@ static void update_fr0_op(CPUHPPAState *env, uintptr_t ra)
 {
     uint32_t soft_exp = get_float_exception_flags(&env->fp_status);
     uint32_t hard_exp = 0;
-    uint32_t shadow = env->fr0_shadow;
+    uint32_t shadow = env->fr0_shadow & 0x3ffffff;
+    uint32_t fr1 = 0;
 
     if (likely(soft_exp == 0)) {
         env->fr[0] = (uint64_t)shadow << 32;
@@ -108,9 +109,22 @@ static void update_fr0_op(CPUHPPAState *env, uintptr_t ra)
     hard_exp |= CONVERT_BIT(soft_exp, float_flag_overflow,  R_FPSR_ENA_O_MASK);
     hard_exp |= CONVERT_BIT(soft_exp, float_flag_divbyzero, R_FPSR_ENA_Z_MASK);
     hard_exp |= CONVERT_BIT(soft_exp, float_flag_invalid,   R_FPSR_ENA_V_MASK);
-    shadow |= hard_exp << (R_FPSR_FLAGS_SHIFT - R_FPSR_ENABLES_SHIFT);
+    if (hard_exp & shadow) {
+        shadow = FIELD_DP32(shadow, FPSR, T, 1);
+        /* fill exception register #1, which is lower 32-bits of fr[0] */
+#if !defined(CONFIG_USER_ONLY)
+        if (hard_exp & (R_FPSR_ENA_O_MASK | R_FPSR_ENA_U_MASK)) {
+            /* over- and underflow both set overflow flag only */
+            fr1 = FIELD_DP32(fr1, FPSR, C, 1);
+            fr1 = FIELD_DP32(fr1, FPSR, FLG_O, 1);
+        } else
+#endif
+        {
+            fr1 |= hard_exp << (R_FPSR_FLAGS_SHIFT - R_FPSR_ENABLES_SHIFT);
+        }
+    }
     env->fr0_shadow = shadow;
-    env->fr[0] = (uint64_t)shadow << 32;
+    env->fr[0] = (uint64_t)shadow << 32 | fr1;
 
     if (hard_exp & shadow) {
         hppa_dynamic_excp(env, EXCP_ASSIST, ra);
-- 
2.47.0