[PATCH v3 1/2] linux-user/s390x: signal with SIGFPE on compare-and-trap

[Jonathan Albrecht <jonathan.albrecht@linux.vnet.ibm.com>]

Currently when a compare-and-trap instruction is executed, qemu will
always raise a SIGILL signal. On real hardware, a SIGFPE is raised.

Change the PGM_DATA case in cpu_loop to follow the behavior in
linux kernel /arch/s390/kernel/traps.c.
 * Only raise SIGILL if DXC == 0
 * If DXC matches a non-simulated IEEE exception, raise SIGFPE with
   correct si_code
 * Raise SIGFPE with si_code == 0 for everything else

When applied on 20210705210434.45824-2-iii@linux.ibm.com, this fixes
crashes in the java jdk such as the linked bug.

Buglink: https://bugs.launchpad.net/qemu/+bug/1920913
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/319
Signed-off-by: Jonathan Albrecht <jonathan.albrecht@linux.vnet.ibm.com>
---
 linux-user/s390x/cpu_loop.c | 54 +++++++++++++++++++++++--------------
 1 file changed, 34 insertions(+), 20 deletions(-)

diff --git a/linux-user/s390x/cpu_loop.c b/linux-user/s390x/cpu_loop.c
index 22f2e89c62..6a69a6dd26 100644
--- a/linux-user/s390x/cpu_loop.c
+++ b/linux-user/s390x/cpu_loop.c
@@ -25,6 +25,35 @@
 /* s390x masks the fault address it reports in si_addr for SIGSEGV and SIGBUS */
 #define S390X_FAIL_ADDR_MASK -4096LL
 
+static int get_pgm_data_si_code(int dxc_code)
+{
+    switch (dxc_code) {
+    /* Non-simulated IEEE exceptions */
+    case 0x80:
+        return TARGET_FPE_FLTINV;
+    case 0x40:
+        return TARGET_FPE_FLTDIV;
+    case 0x20:
+    case 0x28:
+    case 0x2c:
+        return TARGET_FPE_FLTOVF;
+    case 0x10:
+    case 0x18:
+    case 0x1c:
+        return TARGET_FPE_FLTUND;
+    case 0x08:
+    case 0x0c:
+        return TARGET_FPE_FLTRES;
+    }
+    /*
+     * Non-IEEE and simulated IEEE:
+     * Includes compare-and-trap, quantum exception, etc.
+     * Simulated IEEE are included here to match current
+     * s390x linux kernel.
+     */
+    return 0;
+}
+
 void cpu_loop(CPUS390XState *env)
 {
     CPUState *cs = env_cpu(env);
@@ -106,29 +135,14 @@ void cpu_loop(CPUS390XState *env)
 
             case PGM_DATA:
                 n = (env->fpc >> 8) & 0xff;
-                if (n == 0xff) {
-                    /* compare-and-trap */
+                if (n == 0) {
                     goto do_sigill_opn;
-                } else {
-                    /* An IEEE exception, simulated or otherwise.  */
-                    if (n & 0x80) {
-                        n = TARGET_FPE_FLTINV;
-                    } else if (n & 0x40) {
-                        n = TARGET_FPE_FLTDIV;
-                    } else if (n & 0x20) {
-                        n = TARGET_FPE_FLTOVF;
-                    } else if (n & 0x10) {
-                        n = TARGET_FPE_FLTUND;
-                    } else if (n & 0x08) {
-                        n = TARGET_FPE_FLTRES;
-                    } else {
-                        /* ??? Quantum exception; BFP, DFP error.  */
-                        goto do_sigill_opn;
-                    }
-                    sig = TARGET_SIGFPE;
-                    goto do_signal_pc;
                 }
 
+                sig = TARGET_SIGFPE;
+                n = get_pgm_data_si_code(n);
+                goto do_signal_pc;
+
             default:
                 fprintf(stderr, "Unhandled program exception: %#x\n", n);
                 cpu_dump_state(cs, stderr, 0);
-- 
2.31.1