Re: compile warning in i8259.c

[Thomas Huth <thuth@redhat.com>]

On 15/03/2021 16.44, Christian Borntraeger wrote:
> On 15.03.21 16:14, Christian Borntraeger wrote:
>> For some time now I do see the following, when I compile x86-softmmu on s390:
>>
>> FAILED: libcommon.fa.p/hw_intc_i8259.c.o
>> cc -Ilibcommon.fa.p -I. -I.. -Iqapi -Itrace -Iui -Iui/shader 
>> -I/usr/include/capstone -I/usr/include/glib-2.0 
>> -I/usr/lib64/glib-2.0/include -I/usr/include/libmount -I/usr/include/blkid 
>> -I/usr/include/gio-unix-2.0 -I/usr/include/libusb-1.0 
>> -I/usr/include/vte-2.91 -I/usr/include/pango-1.0 -I/usr/include/harfbuzz 
>> -I/usr/include/freetype2 -I/usr/include/libpng16 -I/usr/include/fribidi 
>> -I/usr/include/libxml2 -I/usr/include/cairo -I/usr/include/pixman-1 
>> -I/usr/include/gtk-3.0 -I/usr/include/gdk-pixbuf-2.0 
>> -I/usr/include/atk-1.0 -I/usr/include/at-spi2-atk/2.0 
>> -I/usr/include/dbus-1.0 -I/usr/lib64/dbus-1.0/include 
>> -I/usr/include/at-spi-2.0 -I/usr/include/virgl -I/usr/include/p11-kit-1 
>> -I/usr/include/SDL2 -I/usr/include/cacard -I/usr/include/nss3 
>> -I/usr/include/nspr4 -I/usr/include/slirp -fdiagnostics-color=auto -pipe 
>> -Wall -Winvalid-pch -Werror -std=gnu99 -O2 -g -isystem 
>> /home/cborntra/REPOS/qemu/linux-headers -isystem linux-headers -iquote . 
>> -iquote /home/cborntra/REPOS/qemu -iquote 
>> /home/cborntra/REPOS/qemu/include -iquote 
>> /home/cborntra/REPOS/qemu/disas/libvixl -iquote 
>> /home/cborntra/REPOS/qemu/tcg/s390 -iquote 
>> /home/cborntra/REPOS/qemu/accel/tcg -pthread -U_FORTIFY_SOURCE 
>> -D_FORTIFY_SOURCE=2 -m64 -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 
>> -D_LARGEFILE_SOURCE -Wstrict-prototypes -Wredundant-decls -Wundef 
>> -Wwrite-strings -Wmissing-prototypes -fno-strict-aliasing -fno-common 
>> -fwrapv -Wold-style-declaration -Wold-style-definition -Wtype-limits 
>> -Wformat-security -Wformat-y2k -Winit-self -Wignored-qualifiers 
>> -Wempty-body -Wnested-externs -Wendif-labels -Wexpansion-to-defined 
>> -Wimplicit-fallthrough=2 -Wno-missing-include-dirs 
>> -Wno-shift-negative-value -Wno-psabi -fstack-protector-strong -fPIC 
>> -DSTRUCT_IOVEC_DEFINED -D_REENTRANT -Wno-undef -D_DEFAULT_SOURCE 
>> -D_XOPEN_SOURCE=600 -DNCURSES_WIDECHAR -MD -MQ 
>> libcommon.fa.p/hw_intc_i8259.c.o -MF libcommon.fa.p/hw_intc_i8259.c.o.d -o 
>> libcommon.fa.p/hw_intc_i8259.c.o -c ../hw/intc/i8259.c
>> ../hw/intc/i8259.c: In function ‘pic_read_irq’:
>> ../hw/intc/i8259.c:203:13: error: ‘irq2’ may be used uninitialized in this 
>> function [-Werror=maybe-uninitialized]
>>    203 |         irq = irq2 + 8;
>>        |         ~~~~^~~~~~~~~~
>> cc1: all warnings being treated as errors
>>
>>
>> Due to other compile warnings I find this hard to bisect. Has anyone seen 
>> this as well?
> 
> cc Michael, Paolo,
> 
> Something like
> 
> diff --git a/hw/intc/i8259.c b/hw/intc/i8259.c
> index 344fd04db14d..7335b7a06a67 100644
> --- a/hw/intc/i8259.c
> +++ b/hw/intc/i8259.c
> @@ -176,7 +176,7 @@ static void pic_intack(PICCommonState *s, int irq)
>   int pic_read_irq(DeviceState *d)
>   {
>       PICCommonState *s = PIC_COMMON(d);
> -    int irq, irq2, intno;
> +    int irq, irq2 = 0, intno;
> 
>       irq = pic_get_irq(s);
>       if (irq >= 0) {
> 
> 
> would do the trick. Let me know if I should do a proper patch or if you want 
> to have things solved differently.

Alternate idea, merge the two "irq == 2" blocks:

diff a/hw/intc/i8259.c b/hw/intc/i8259.c
--- a/hw/intc/i8259.c
+++ b/hw/intc/i8259.c
@@ -179,19 +179,19 @@ int pic_read_irq(DeviceState *d)
      int irq, irq2, intno;

      irq = pic_get_irq(s);
-    if (irq >= 0) {
-        if (irq == 2) {
-            irq2 = pic_get_irq(slave_pic);
-            if (irq2 >= 0) {
-                pic_intack(slave_pic, irq2);
-            } else {
-                /* spurious IRQ on slave controller */
-                irq2 = 7;
-            }
-            intno = slave_pic->irq_base + irq2;
+    if (irq == 2) {
+        irq2 = pic_get_irq(slave_pic);
+        if (irq2 >= 0) {
+            pic_intack(slave_pic, irq2);
          } else {
-            intno = s->irq_base + irq;
+            /* spurious IRQ on slave controller */
+            irq2 = 7;
          }
+        intno = slave_pic->irq_base + irq2;
+        pic_intack(s, irq);
+        irq = irq2 + 8;
+    } else if (irq >= 0) {
+        intno = s->irq_base + irq;
          pic_intack(s, irq);
      } else {
          /* spurious IRQ on host controller */
@@ -199,10 +199,6 @@ int pic_read_irq(DeviceState *d)
          intno = s->irq_base + irq;
      }

-    if (irq == 2) {
-        irq = irq2 + 8;
-    }
-
  #ifdef DEBUG_IRQ_LATENCY
      printf("IRQ%d latency=%0.3fus\n",
             irq,

It's a bigger patch, but the code is IMHO easier to read afterwards (less 
indentation).

  Thomas