Re: [PATCH 5/6] hw/scsi/megasas: Silent GCC9 duplicated-cond warning

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 12/18/19 5:03 AM, Richard Henderson wrote:
> On 12/17/19 7:34 AM, Philippe Mathieu-Daudé wrote:
>> GCC9 is confused when building with CFLAG -O3:
>>
>>    hw/scsi/megasas.c: In function ‘megasas_scsi_realize’:
>>    hw/scsi/megasas.c:2387:26: error: duplicated ‘if’ condition [-Werror=duplicated-cond]
>>     2387 |     } else if (s->fw_sge >= 128 - MFI_PASS_FRAME_SIZE) {
>>    hw/scsi/megasas.c:2385:19: note: previously used here
>>     2385 |     if (s->fw_sge >= MEGASAS_MAX_SGE - MFI_PASS_FRAME_SIZE) {
>>    cc1: all warnings being treated as errors
>>
>> When this device was introduced in commit e8f943c3bcc, the author
>> cared about modularity, using a definition for the firmware limit.
>> If we modify the limit, the code is valid. Add a check if the
>> definition got modified to a bigger limit.
>>
>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>> ---
>> Cc: Hannes Reinecke <hare@suse.com>
>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>> Cc: Fam Zheng <fam@euphon.net>
>> Cc: qemu-block@nongnu.org
>> ---
>>   hw/scsi/megasas.c | 3 ++-
>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/scsi/megasas.c b/hw/scsi/megasas.c
>> index de9bd20887..ece1601b66 100644
>> --- a/hw/scsi/megasas.c
>> +++ b/hw/scsi/megasas.c
>> @@ -2382,7 +2382,8 @@ static void megasas_scsi_realize(PCIDevice *dev, Error **errp)
>>       if (!s->hba_serial) {
>>           s->hba_serial = g_strdup(MEGASAS_HBA_SERIAL);
>>       }
>> -    if (s->fw_sge >= MEGASAS_MAX_SGE - MFI_PASS_FRAME_SIZE) {
>> +    if (MEGASAS_MAX_SGE > 128
>> +        && s->fw_sge >= MEGASAS_MAX_SGE - MFI_PASS_FRAME_SIZE) {
>>           s->fw_sge = MEGASAS_MAX_SGE - MFI_PASS_FRAME_SIZE;
>>       } else if (s->fw_sge >= 128 - MFI_PASS_FRAME_SIZE) {
>>           s->fw_sge = 128 - MFI_PASS_FRAME_SIZE;
>>
> 
> I'm not keen on this.  It looks to me like the raw 128 case should be removed
> -- surely that's the point of the symbolic constant.  But I'll defer if a
> maintainer disagrees.

Is that approach acceptable?

-- >8 --
@@ -54,6 +54,9 @@
  #define MEGASAS_FLAG_USE_QUEUE64   1
  #define MEGASAS_MASK_USE_QUEUE64   (1 << MEGASAS_FLAG_USE_QUEUE64)

+QEMU_BUILD_BUG_MSG(MEGASAS_MAX_SGE > 128,
+                   "Firmware limit too big for this device model");
+
  static const char *mfi_frame_desc[] = {
      "MFI init", "LD Read", "LD Write", "LD SCSI", "PD SCSI",
      "MFI Doorbell", "MFI Abort", "MFI SMP", "MFI Stop"};
@@ -2382,9 +2385,7 @@ static void megasas_scsi_realize(PCIDevice *dev, 
Error **errp)
      if (!s->hba_serial) {
          s->hba_serial = g_strdup(MEGASAS_HBA_SERIAL);
      }
-    if (s->fw_sge >= MEGASAS_MAX_SGE - MFI_PASS_FRAME_SIZE) {
-        s->fw_sge = MEGASAS_MAX_SGE - MFI_PASS_FRAME_SIZE;
-    } else if (s->fw_sge >= 128 - MFI_PASS_FRAME_SIZE) {
+    if (s->fw_sge >= 128 - MFI_PASS_FRAME_SIZE) {
          s->fw_sge = 128 - MFI_PASS_FRAME_SIZE;
      } else {
          s->fw_sge = 64 - MFI_PASS_FRAME_SIZE;
---