Re: [Qemu-devel] [PATCH] s390x: silence warning from GCC on uninitialized values

[Cornelia Huck]

On Mon, 04 Feb 2013 22:57:43 +0100
Stefan Weil <address@hidden> wrote:

> Am 04.02.2013 22:23, schrieb Anthony Liguori:
> > As best I can tell, this is a false positive.
> >
> >   address@hidden qemu-s390]$ make
> >     CC    s390x-softmmu/target-s390x/helper.o
> >   /home/aliguori/git/qemu/target-s390x/helper.c: In function ‘do_interrupt’:
> >   /home/aliguori/git/qemu/target-s390x/helper.c:673:17: error: ‘addr’ may 
> > be used uninitialized in this function [-Werror=maybe-uninitialized]
> >   /home/aliguori/git/qemu/target-s390x/helper.c:620:20: note: ‘addr’ was 
> > declared here
> >   /home/aliguori/git/qemu/target-s390x/helper.c:673:17: error: ‘mask’ may 
> > be used uninitialized in this function [-Werror=maybe-uninitialized]
> >   /home/aliguori/git/qemu/target-s390x/helper.c:620:14: note: ‘mask’ was 
> > declared here
> >   cc1: all warnings being treated as errors
> >   make[1]: *** [target-s390x/helper.o] Error 1
> >   make: *** [subdir-s390x-softmmu] Error 2
> >
> 
> Yes, this is a false positive. A better compiler will complain when your
> patch was applied because addr, mask are assigned values which are
> never used...
> 
> Would it be possible to completely eliminate variable "found" and
> move the DPRINTF, load_psw statements into the for loop (just before
> the break statement)?

We could move the lpsw. However, this made me notice another problem:
We stop scanning subsequent iscs if we found an interrupt to inject...

This is not a problem for current virtio-ccw based Linux guests since
they never use anything else than isc 3, but we'll probably want the
following patch.

From 8b2f40e8eaac16b55a72ab1e36a4c5de0b016495 Mon Sep 17 00:00:00 2001
From: Cornelia Huck <address@hidden>
Date: Tue, 5 Feb 2013 10:14:49 +0100
Subject: [PATCH] s390: Keep I/O interrupts enabled for all iscs.

do_io_interrupt() would stop scanning further iscs if it found
an I/O interrupt it could inject. This might cause the pending
interrupt indication for I/O interrupts to be reset although there
might be queued I/O interrupts for subsequent iscs.

Fix this by reordering the logic: Inject the I/O interrupt immediately
and continue searching all iscs for queued interrupts.

Signed-off-by: Cornelia Huck <address@hidden>
---
 target-s390x/helper.c | 40 +++++++++++++++++++++-------------------
 1 file changed, 21 insertions(+), 19 deletions(-)

diff --git a/target-s390x/helper.c b/target-s390x/helper.c
index 043feb2..9f9088b 100644
--- a/target-s390x/helper.c
+++ b/target-s390x/helper.c
@@ -617,7 +617,6 @@ static void do_ext_interrupt(CPUS390XState *env)
 
 static void do_io_interrupt(CPUS390XState *env)
 {
-    uint64_t mask = 0, addr = 0;
     LowCore *lowcore;
     IOIntQueue *q;
     uint8_t isc;
@@ -642,36 +641,39 @@ static void do_io_interrupt(CPUS390XState *env)
             disable = 0;
             continue;
         }
-        found = 1;
-        lowcore = cpu_map_lowcore(env);
+        if (!found) {
+            uint64_t mask, addr;
 
-        lowcore->subchannel_id = cpu_to_be16(q->id);
-        lowcore->subchannel_nr = cpu_to_be16(q->nr);
-        lowcore->io_int_parm = cpu_to_be32(q->parm);
-        lowcore->io_int_word = cpu_to_be32(q->word);
-        lowcore->io_old_psw.mask = cpu_to_be64(get_psw_mask(env));
-        lowcore->io_old_psw.addr = cpu_to_be64(env->psw.addr);
-        mask = be64_to_cpu(lowcore->io_new_psw.mask);
-        addr = be64_to_cpu(lowcore->io_new_psw.addr);
+            found = 1;
+            lowcore = cpu_map_lowcore(env);
 
-        cpu_unmap_lowcore(lowcore);
+            lowcore->subchannel_id = cpu_to_be16(q->id);
+            lowcore->subchannel_nr = cpu_to_be16(q->nr);
+            lowcore->io_int_parm = cpu_to_be32(q->parm);
+            lowcore->io_int_word = cpu_to_be32(q->word);
+            lowcore->io_old_psw.mask = cpu_to_be64(get_psw_mask(env));
+            lowcore->io_old_psw.addr = cpu_to_be64(env->psw.addr);
+            mask = be64_to_cpu(lowcore->io_new_psw.mask);
+            addr = be64_to_cpu(lowcore->io_new_psw.addr);
 
-        env->io_index[isc]--;
+            cpu_unmap_lowcore(lowcore);
+
+            env->io_index[isc]--;
+
+            DPRINTF("%s: %" PRIx64 " %" PRIx64 "\n", __func__,
+                    env->psw.mask, env->psw.addr);
+            load_psw(env, mask, addr);
+        }
         if (env->io_index[isc] >= 0) {
             disable = 0;
         }
-        break;
+        continue;
     }
 
     if (disable) {
         env->pending_int &= ~INTERRUPT_IO;
     }
 
-    if (found) {
-        DPRINTF("%s: %" PRIx64 " %" PRIx64 "\n", __func__,
-                env->psw.mask, env->psw.addr);
-        load_psw(env, mask, addr);
-    }
 }
 
 static void do_mchk_interrupt(CPUS390XState *env)
-- 
1.7.12.4