From: Pan Nengyuan <pannengyuan@huawei.com>

Fixes:
target/arm/translate-a64.c: In function 'disas_crypto_three_reg_sha512':
target/arm/translate-a64.c:13625:9: error: 'genfn' may be used uninitialized in this function [-Werror=maybe-uninitialized]
    genfn(tcg_rd_ptr, tcg_rn_ptr, tcg_rm_ptr);
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
qemu/target/arm/translate-a64.c:13609:8: error: 'feature' may be used uninitialized in this function [-Werror=maybe-uninitialized]
    if (!feature) {

Reported-by: Euler Robot <euler.robot@huawei.com>
Signed-off-by: Pan Nengyuan <pannengyuan@huawei.com>
Cc: Peter Maydell <peter.maydell@linaro.org> 
---
 target/arm/translate-a64.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c
index d4bebbe629..211e3d813f 100644
--- a/target/arm/translate-a64.c
+++ b/target/arm/translate-a64.c
@@ -13564,8 +13564,8 @@ static void disas_crypto_three_reg_sha512(DisasContext *s, uint32_t insn)
     int rm = extract32(insn, 16, 5);
     int rn = extract32(insn, 5, 5);
     int rd = extract32(insn, 0, 5);
-    bool feature;
-    CryptoThreeOpFn *genfn;
+    bool feature = false;
+    CryptoThreeOpFn *genfn = NULL;
 
     if (o == 0) {
         switch (opcode) {
-- 
2.21.0.windows.1

On 1/6/20 11:57 AM, pannengyuan@huawei.com wrote:
> From: Pan Nengyuan <pannengyuan@huawei.com>
> 
> Fixes:
> target/arm/translate-a64.c: In function 'disas_crypto_three_reg_sha512':
> target/arm/translate-a64.c:13625:9: error: 'genfn' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>     genfn(tcg_rd_ptr, tcg_rn_ptr, tcg_rm_ptr);
>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> qemu/target/arm/translate-a64.c:13609:8: error: 'feature' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>     if (!feature) {
> 
> Reported-by: Euler Robot <euler.robot@huawei.com>
> Signed-off-by: Pan Nengyuan <pannengyuan@huawei.com>
> Cc: Peter Maydell <peter.maydell@linaro.org> 

Are you compiling with reduced optimization?  The compiler should be able to
prove that these variables are initialized.  It certainly does with -O2, on all
known gcc versions.

Perhaps a better fix is to add a

    default:
        g_assert_not_reached();

entry to the o == 0 switch.  Though of course opcode must be in [0-3], based on
the extraction mask, so a default label isn't actually reachable.  But that's
the only path I can see for which incomplete optimization would fail to prove
initialization.


r~

On 1/6/2020 10:15 AM, Richard Henderson wrote:
> On 1/6/20 11:57 AM, pannengyuan@huawei.com wrote:
>> From: Pan Nengyuan <pannengyuan@huawei.com>
>>
>> Fixes:
>> target/arm/translate-a64.c: In function 'disas_crypto_three_reg_sha512':
>> target/arm/translate-a64.c:13625:9: error: 'genfn' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>>     genfn(tcg_rd_ptr, tcg_rn_ptr, tcg_rm_ptr);
>>     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> qemu/target/arm/translate-a64.c:13609:8: error: 'feature' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>>     if (!feature) {
>>
>> Reported-by: Euler Robot <euler.robot@huawei.com>
>> Signed-off-by: Pan Nengyuan <pannengyuan@huawei.com>
>> Cc: Peter Maydell <peter.maydell@linaro.org> 
> 
> Are you compiling with reduced optimization?  The compiler should be able to
> prove that these variables are initialized.  It certainly does with -O2, on all
> known gcc versions.

Yes, I compile it with optimization flags (-O2) and get this warnings. The gcc version is 8.2.1.

> 
> Perhaps a better fix is to add a
> 
>     default:
>         g_assert_not_reached();
> 
> entry to the o == 0 switch.  Though of course opcode must be in [0-3], based on
> the extraction mask, so a default label isn't actually reachable.  But that's
> the only path I can see for which incomplete optimization would fail to prove
> initializatio
Yes, a default label is a better way.

> 
> r~
>