Re: [PATCH] hw/mips/malta: Silence warning from ubsan

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

Hi Thomas,

On 28/7/25 13:51, Thomas Huth wrote:
> From: Thomas Huth <thuth@redhat.com>
> 
> When compiling QEMU with --enable-ubsan there is a undefined behavior
> warning when using the malta machine:
> 
>   hw/mips/malta.c:1200:32: runtime error: addition of unsigned offset
>    to 0x7fb620600000 overflowed to 0x7fb6205fffff
>   SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior hw/mips/malta.c:1200:32
> 
> To fix the issue, check the bios_size whether we really loaded the
> firmware before trying to byte-swap the instructions here.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>   hw/mips/malta.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/hw/mips/malta.c b/hw/mips/malta.c
> index cbdbb210568..47dd4016cfd 100644
> --- a/hw/mips/malta.c
> +++ b/hw/mips/malta.c
> @@ -1190,7 +1190,7 @@ void mips_malta_init(MachineState *machine)
>            * In little endian mode the 32bit words in the bios are swapped,
>            * a neat trick which allows bi-endian firmware.
>            */
> -        if (!TARGET_BIG_ENDIAN) {
> +        if (!TARGET_BIG_ENDIAN && bios_size > 0) {
>               uint32_t *end, *addr;
>               const size_t swapsize = MIN(bios_size, 0x3e0000);
>               addr = rom_ptr(FLASH_ADDRESS, swapsize);

What about:

-- >8 --
@@ -1180,7 +1180,7 @@ void mips_malta_init(MachineState *machine)
              } else {
                  bios_size = -1;
              }
-            if ((bios_size < 0 || bios_size > BIOS_SIZE) &&
+            if ((bios_size <= 0 || bios_size > BIOS_SIZE) &&
                  machine->firmware && !qtest_enabled()) {
                  error_report("Could not load MIPS bios '%s'", 
machine->firmware);
                  exit(1);
---

?