Re: [PATCH 0/4] ppc: valgrind "uninitialized values" fixes

[Philippe Mathieu-Daudé]

On 30/3/22 23:04, Daniel Henrique Barboza wrote:
> Hi,
>
> These are a handful of trivial fixes to make Valgrind happier when
> profiling the boot of a pSeries guest. All the patches are handling a
> similar case where we have something similar to this:
>
> ---
> uint64_t val;
>
> (...)
>
> kvm_vcpu_ioctl(...., &val);

Which is a false positive.

> ---
>
> Valgrind does not consider that 'val' was initialized and then it keeps
> complaining about every future use of 'val', or anything that got
> assigned as 'val', as being an uninitialized value/data. The fix is
> simple and without any side effects:: just initialize 'val'.

I gave a try to some definition but the result is rather ugly =)

-- >8 --
diff --git a/include/qemu/compiler.h b/include/qemu/compiler.h
index d9359859d4..85429930fb 100644
--- a/include/qemu/compiler.h
+++ b/include/qemu/compiler.h
@@ -194,4 +194,10 @@ extern void QEMU_NORETURN QEMU_ERROR("code path is 
reachable")
 #define QEMU_DISABLE_CFI
 #endif

+#ifdef QEMU_STATIC_ANALYSIS
+#define QEMU_UNNECESSARY_INIT(values...) = values
+#else
+#define QEMU_UNNECESSARY_INIT(values...)
+#endif
+
 #endif /* COMPILER_H */
diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
index dc93b99189..97aec29694 100644
--- a/target/ppc/kvm.c
+++ b/target/ppc/kvm.c
@@ -546,7 +546,7 @@ static void kvm_get_one_spr(CPUState *cs, uint64_t 
id, int spr)
     union {
         uint32_t u32;
         uint64_t u64;
-    } val;
+    } val QEMU_UNNECESSARY_INIT({ });
     struct kvm_one_reg reg = {
         .id = id,
         .addr = (uintptr_t) &val,
---

Being able to use valgrind is more valuable that these unnecessary
init, so:
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>