On 04/14/19 10:03, Jordan Justen wrote:
> On 2019-04-12 16:31:26, Laszlo Ersek wrote:
>> RH covscan warns about assignments that it can determine are never
>> "consumed" later ("dead stores"). The idea behind the warning is
>> presumably that the programmer forgot to implement a dependent check
>> somewhere.
>>
>> For each such warning that has been emitted for OvmfPkg,
>> the case is one of the following however:
>>
>> - We assign a variable a value for (re-)initialization's sake, in
>> preparation for further or future uses. This practice is safe (sometimes
>> even recommended!), hence we should suppress these warnings.
>>
>> - We capture a result or a computation in a variable, following a general
>> programming pattern, but then decide to ignore the value in that
>> particular case. This is again safe, and we should suppress these
>> warnings too.
>>
>> According to the Clang documentation at
>>
>> https://clang-analyzer.llvm.org/faq.html#dead_store
>>
>> we should use
>>
>> (void)x;
>>
>> See the logs below (produced originally for edk2-stable201903).
>>
>>> Error: CLANG_WARNING:
>>> edk2-89910a39dcfd/OvmfPkg/AcpiPlatformDxe/Xen.c:156:3: warning: Value
>>> stored to 'NumberOfTableEntries' is never read
>>> # NumberOfTableEntries = 0;
>>> # ^ ~
>>> edk2-89910a39dcfd/OvmfPkg/AcpiPlatformDxe/Xen.c:156:3: note: Value
>>> stored to 'NumberOfTableEntries' is never read
>>> # NumberOfTableEntries = 0;
>>> # ^ ~
>>> # 154| DsdtTable = NULL;
>>> # 155| TableHandle = 0;
>>> # 156|-> NumberOfTableEntries = 0;
>>> # 157|
>>> # 158| //
>>>
>>> Error: CLANG_WARNING:
>>> edk2-89910a39dcfd/OvmfPkg/Library/PlatformBootManagerLib/QemuKernel.c:43:3:
>>> warning: Value stored to 'SetupSize' is never read
>>> # SetupSize = 0;
>>> # ^ ~
>>> edk2-89910a39dcfd/OvmfPkg/Library/PlatformBootManagerLib/QemuKernel.c:43:3:
>>> note: Value stored to 'SetupSize' is never read
>>> # SetupSize = 0;
>>> # ^ ~
>>> # 41|
>>> # 42| SetupBuf = NULL;
>>> # 43|-> SetupSize = 0;
>>> # 44| KernelBuf = NULL;
>>> # 45| KernelInitialSize = 0;
>>>
>>> Error: CLANG_WARNING:
>>> edk2-89910a39dcfd/OvmfPkg/Library/SerializeVariablesLib/SerializeVariablesLib.c:609:9:
>>> warning: Value stored to 'VariableDataBufferSize' is never read
>>> # VariableDataBufferSize = 0;
>>> # ^ ~
>>> edk2-89910a39dcfd/OvmfPkg/Library/SerializeVariablesLib/SerializeVariablesLib.c:609:9:
>>> note: Value stored to 'VariableDataBufferSize' is never read
>>> # VariableDataBufferSize = 0;
>>> # ^ ~
>>> # 607| FreePool (VariableData);
>>> # 608| VariableData = NULL;
>>> # 609|-> VariableDataBufferSize = 0;
>>> # 610| }
>>> # 611| VariableData = AllocatePool (VariableDataSize);
>>>
>>> Error: CLANG_WARNING:
>>> edk2-89910a39dcfd/OvmfPkg/Library/VirtioLib/VirtioLib.c:125:3: warning:
>>> Value stored to 'RingPagesPtr' is never read
>>> # RingPagesPtr += sizeof *Ring->Used.AvailEvent;
>>> # ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>> edk2-89910a39dcfd/OvmfPkg/Library/VirtioLib/VirtioLib.c:125:3: note:
>>> Value stored to 'RingPagesPtr' is never read
>>> # RingPagesPtr += sizeof *Ring->Used.AvailEvent;
>>> # ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>> # 123|
>>> # 124| Ring->Used.AvailEvent = (volatile VOID *) RingPagesPtr;
>>> # 125|-> RingPagesPtr += sizeof *Ring->Used.AvailEvent;
>>> # 126|
>>> # 127| Ring->QueueSize = QueueSize;
>>>
>>> Error: CLANG_WARNING:
>>> edk2-89910a39dcfd/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockService.c:1079:3:
>>> warning: Value stored to 'FwhInstance' is never read
>>> # FwhInstance = (EFI_FW_VOL_INSTANCE *)
>>> # ^ ~~~~~~~~~~~~~~~~~~~~~~~
>>> edk2-89910a39dcfd/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockService.c:1079:3:
>>> note: Value stored to 'FwhInstance' is never read
>>> # FwhInstance = (EFI_FW_VOL_INSTANCE *)
>>> # ^ ~~~~~~~~~~~~~~~~~~~~~~~
>>> # 1077| ASSERT_RETURN_ERROR (PcdStatus);
>>> # 1078|
>>> # 1079|-> FwhInstance = (EFI_FW_VOL_INSTANCE *)
>>> # 1080| (
>>> # 1081| (UINTN) ((UINT8 *) FwhInstance) + FwVolHeader->HeaderLength
>>> +
>>>
>>> Error: CLANG_WARNING:
>>> edk2-89910a39dcfd/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockServiceDxe.c:173:3:
>>> warning: Value stored to 'Status' is never read
>>> # Status = gDS->RemoveMemorySpace (
>>> # ^ ~~~~~~~~~~~~~~~~~~~~~~~~
>>> edk2-89910a39dcfd/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockServiceDxe.c:173:3:
>>> note: Value stored to 'Status' is never read
>>> # Status = gDS->RemoveMemorySpace (
>>> # ^ ~~~~~~~~~~~~~~~~~~~~~~~~
>>> # 171| // Mark flash region as runtime memory
>>> # 172| //
>>> # 173|-> Status = gDS->RemoveMemorySpace (
>>> # 174| BaseAddress,
>>> # 175| Length
>>>
>>> Error: CLANG_WARNING:
>>> edk2-89910a39dcfd/OvmfPkg/SataControllerDxe/SataController.c:231:3:
>>> warning: Value stored to 'DeviceUDmaMode' is never read
>>> # DeviceUDmaMode = 0;
>>> # ^ ~
>>> edk2-89910a39dcfd/OvmfPkg/SataControllerDxe/SataController.c:231:3:
>>> note: Value stored to 'DeviceUDmaMode' is never read
>>> # DeviceUDmaMode = 0;
>>> # ^ ~
>>> # 229| UINT16 DeviceUDmaMode;
>>> # 230|
>>> # 231|-> DeviceUDmaMode = 0;
>>> # 232|
>>> # 233| //
>>>
>>> Error: CLANG_WARNING:
>>> edk2-89910a39dcfd/OvmfPkg/VirtioGpuDxe/Gop.c:65:5: warning: Value stored
>>> to 'Status' is never read
>>> # Status = VirtioGpuSetScanout (
>>> # ^ ~~~~~~~~~~~~~~~~~~~~~
>>> edk2-89910a39dcfd/OvmfPkg/VirtioGpuDxe/Gop.c:65:5: note: Value stored to
>>> 'Status' is never read
>>> # Status = VirtioGpuSetScanout (
>>> # ^ ~~~~~~~~~~~~~~~~~~~~~
>>> # 63| // by setting ResourceId=0 for it.
>>> # 64| //
>>> # 65|-> Status = VirtioGpuSetScanout (
>>> # 66| VgpuGop->ParentBus, // VgpuDev
>>> # 67| 0, 0, 0, 0, // X, Y, Width, Height
>>>
>>> Error: CLANG_WARNING:
>>> edk2-89910a39dcfd/OvmfPkg/VirtioNetDxe/SnpReceive.c:165:3: warning:
>>> Value stored to 'RxPtr' is never read
>>> # RxPtr += sizeof (UINT16);
>>> # ^ ~~~~~~~~~~~~~~~
>>> edk2-89910a39dcfd/OvmfPkg/VirtioNetDxe/SnpReceive.c:165:3: note: Value
>>> stored to 'RxPtr' is never read
>>> # RxPtr += sizeof (UINT16);
>>> # ^ ~~~~~~~~~~~~~~~
>>> # 163| *Protocol = (UINT16) ((RxPtr[0] << 8) | RxPtr[1]);
>>> # 164| }
>>> # 165|-> RxPtr += sizeof (UINT16);
>>> # 166|
>>> # 167| Status = EFI_SUCCESS;
>>
>> Cc: Anthony Perard <anthony.per...@citrix.com>
>> Cc: Ard Biesheuvel <ard.biesheu...@linaro.org>
>> Cc: Jordan Justen <jordan.l.jus...@intel.com>
>> Cc: Julien Grall <julien.gr...@arm.com>
>> Bugzilla: https://bugzilla.tianocore.org/show_bug.cgi?id=1710
>> Issue: scan-0992.txt
>> Issue: scan-0996.txt
>> Issue: scan-0997.txt
>> Issue: scan-0998.txt
>> Issue: scan-1000.txt
>> Issue: scan-1001.txt
>> Issue: scan-1006.txt
>> Issue: scan-1011.txt
>> Issue: scan-1012.txt
>> Signed-off-by: Laszlo Ersek <ler...@redhat.com>
>> ---
>> OvmfPkg/AcpiPlatformDxe/Xen.c | 5 +++++
>> OvmfPkg/Library/PlatformBootManagerLib/QemuKernel.c | 5 +++++
>> OvmfPkg/Library/SerializeVariablesLib/SerializeVariablesLib.c | 4 ++++
>> OvmfPkg/Library/VirtioLib/VirtioLib.c | 5 +++++
>> OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockService.c | 5 +++++
>> OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockServiceDxe.c | 5 +++++
>> OvmfPkg/SataControllerDxe/SataController.c | 5 +++++
>> OvmfPkg/VirtioGpuDxe/Gop.c | 6 ++++++
>> OvmfPkg/VirtioNetDxe/SnpReceive.c | 5 +++++
>> 9 files changed, 45 insertions(+)
>>
>> diff --git a/OvmfPkg/AcpiPlatformDxe/Xen.c b/OvmfPkg/AcpiPlatformDxe/Xen.c
>> index 357c60d23f4e..c8f275a8ee84 100644
>> --- a/OvmfPkg/AcpiPlatformDxe/Xen.c
>> +++ b/OvmfPkg/AcpiPlatformDxe/Xen.c
>> @@ -144,16 +144,21 @@ InstallXenTables (
>> Fadt2Table = NULL;
>> Fadt1Table = NULL;
>> Facs2Table = NULL;
>> Facs1Table = NULL;
>> DsdtTable = NULL;
>> TableHandle = 0;
>> NumberOfTableEntries = 0;
>>
>> + //
>> + // Suppress "Value stored to ... is never read" analyzer warnings.
>> + //
>> + (VOID)NumberOfTableEntries;
>> +
>
> I've seen this solution to shut up the compiler for similar reasons,
> and it kind of bugs me.
>
> It looks like both paths of the if & else initialize
> NumberOfTableEntries, so maybe we can just drop setting it to 0?
It might trigger *other* compilers to whine about "variable read without
initialization" :)
> I looked at FwhInstance too, and it doesn't look like it is used after
> being set. So, maybe that should just be dropped?
>
> I guess both of your bullet points give arguments allowing the unused
> set.
>
> Rather than adding "Suppress..." comments everywhere, maybe a global
> macro could be defined for similar uses in EDK II?
>
> //
> // Suppress "Value stored to ... is never read" analyzer warnings.
> //
> #define IGNORE_UNUSED_ASSIGNMENT(var) ((VOID)var)
>
> Then again, I guess we decided to suppress this in EDK II compiler
> warnings with -Wno-unused-but-set-variable.
>
> So, can you adjust the RH covscan tool settings to similarly ignore
> these warnings?
I think that should be possible, yes. AIUI it is supposed to have
location-sensitive permanent overrides (maintained outside of the source
code), and it should be doing incremental / differential scanning --
report only "new" issues.
Admittedly, I hate most of the warning suppression patches myself,
littering our code -- and that applies to all the *historical* spurious
assignments that we already have in place --, so I'm 100% fine with
dropping this patch (and other suppression patches too, if that is the
upstream edk2 project's preference!)
Thanks!
Laszlo
>> //
>> // Try to find Xen ACPI tables
>> //
>> Status = GetXenAcpiRsdp (&XenAcpiRsdpStructurePtr);
>> if (EFI_ERROR (Status)) {
>> return Status;
>> }
>>
>> diff --git a/OvmfPkg/Library/PlatformBootManagerLib/QemuKernel.c
>> b/OvmfPkg/Library/PlatformBootManagerLib/QemuKernel.c
>> index ddfef925edd3..fde8c40218a4 100644
>> --- a/OvmfPkg/Library/PlatformBootManagerLib/QemuKernel.c
>> +++ b/OvmfPkg/Library/PlatformBootManagerLib/QemuKernel.c
>> @@ -37,16 +37,21 @@ TryRunningQemuKernel (
>> SetupSize = 0;
>> KernelBuf = NULL;
>> KernelInitialSize = 0;
>> CommandLine = NULL;
>> CommandLineSize = 0;
>> InitrdData = NULL;
>> InitrdSize = 0;
>>
>> + //
>> + // Suppress "Value stored to ... is never read" analyzer warnings.
>> + //
>> + (VOID)SetupSize;
>> +
>> if (!QemuFwCfgIsAvailable ()) {
>> return EFI_NOT_FOUND;
>> }
>>
>> QemuFwCfgSelectItem (QemuFwCfgItemKernelSize);
>> KernelSize = (UINTN) QemuFwCfgRead64 ();
>>
>> QemuFwCfgSelectItem (QemuFwCfgItemKernelSetupSize);
>> diff --git a/OvmfPkg/Library/SerializeVariablesLib/SerializeVariablesLib.c
>> b/OvmfPkg/Library/SerializeVariablesLib/SerializeVariablesLib.c
>> index a6cebcb54f6b..64fe9d9be543 100644
>> --- a/OvmfPkg/Library/SerializeVariablesLib/SerializeVariablesLib.c
>> +++ b/OvmfPkg/Library/SerializeVariablesLib/SerializeVariablesLib.c
>> @@ -596,16 +596,20 @@ SerializeVariablesIterateSystemVariables (
>> //
>> // The currently allocated VariableData buffer is too small,
>> // so we allocate a larger buffer.
>> //
>> if (VariableDataBufferSize != 0) {
>> FreePool (VariableData);
>> VariableData = NULL;
>> VariableDataBufferSize = 0;
>> + //
>> + // Suppress "Value stored to ... is never read" analyzer warnings.
>> + //
>> + (VOID)VariableDataBufferSize;
>> }
>> VariableData = AllocatePool (VariableDataSize);
>> if (VariableData == NULL) {
>> Status = EFI_OUT_OF_RESOURCES;
>> break;
>> }
>> VariableDataBufferSize = VariableDataSize;
>>
>> diff --git a/OvmfPkg/Library/VirtioLib/VirtioLib.c
>> b/OvmfPkg/Library/VirtioLib/VirtioLib.c
>> index 555d2a5ce7c9..0e4b8b6b265e 100644
>> --- a/OvmfPkg/Library/VirtioLib/VirtioLib.c
>> +++ b/OvmfPkg/Library/VirtioLib/VirtioLib.c
>> @@ -113,16 +113,21 @@ VirtioRingInit (
>> RingPagesPtr += sizeof *Ring->Used.Idx;
>>
>> Ring->Used.UsedElem = (volatile VOID *) RingPagesPtr;
>> RingPagesPtr += sizeof *Ring->Used.UsedElem * QueueSize;
>>
>> Ring->Used.AvailEvent = (volatile VOID *) RingPagesPtr;
>> RingPagesPtr += sizeof *Ring->Used.AvailEvent;
>>
>> + //
>> + // Suppress "Value stored to ... is never read" analyzer warnings.
>> + //
>> + (VOID)RingPagesPtr;
>> +
>> Ring->QueueSize = QueueSize;
>> return EFI_SUCCESS;
>> }
>>
>>
>> /**
>>
>> Tear down the internal resources of a configured virtio ring.
>> diff --git a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockService.c
>> b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockService.c
>> index edf438a422fa..ff6565865846 100644
>> --- a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockService.c
>> +++ b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockService.c
>> @@ -1071,16 +1071,21 @@ FvbInitialize (
>> ASSERT_RETURN_ERROR (PcdStatus);
>>
>> FwhInstance = (EFI_FW_VOL_INSTANCE *)
>> (
>> (UINTN) ((UINT8 *) FwhInstance) + FwVolHeader->HeaderLength +
>> (sizeof (EFI_FW_VOL_INSTANCE) - sizeof (EFI_FIRMWARE_VOLUME_HEADER))
>> );
>>
>> + //
>> + // Suppress "Value stored to ... is never read" analyzer warnings.
>> + //
>> + (VOID)FwhInstance;
>> +
>> //
>> // Module type specific hook.
>> //
>> InstallVirtualAddressChangeHandler ();
>>
>> PcdStatus = PcdSetBoolS (PcdOvmfFlashVariablesEnable, TRUE);
>> ASSERT_RETURN_ERROR (PcdStatus);
>> return EFI_SUCCESS;
>> diff --git a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockServiceDxe.c
>> b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockServiceDxe.c
>> index 69b20916bc7c..979122f2e2fd 100644
>> --- a/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockServiceDxe.c
>> +++ b/OvmfPkg/QemuFlashFvbServicesRuntimeDxe/FwBlockServiceDxe.c
>> @@ -164,16 +164,21 @@ MarkIoMemoryRangeForRuntimeAccess (
>> //
>> // Mark flash region as runtime memory
>> //
>> Status = gDS->RemoveMemorySpace (
>> BaseAddress,
>> Length
>> );
>>
>> + //
>> + // Suppress "Value stored to ... is never read" analyzer warnings.
>> + //
>> + (VOID)Status;
>> +
>> Status = gDS->AddMemorySpace (
>> EfiGcdMemoryTypeMemoryMappedIo,
>> BaseAddress,
>> Length,
>> EFI_MEMORY_UC | EFI_MEMORY_RUNTIME
>> );
>> ASSERT_EFI_ERROR (Status);
>>
>> diff --git a/OvmfPkg/SataControllerDxe/SataController.c
>> b/OvmfPkg/SataControllerDxe/SataController.c
>> index 8d6a6bbb2286..0cf6b42c886a 100644
>> --- a/OvmfPkg/SataControllerDxe/SataController.c
>> +++ b/OvmfPkg/SataControllerDxe/SataController.c
>> @@ -219,16 +219,21 @@ CalculateBestUdmaMode (
>> OUT UINT16 *SelectedMode
>> )
>> {
>> UINT16 TempMode;
>> UINT16 DeviceUDmaMode;
>>
>> DeviceUDmaMode = 0;
>>
>> + //
>> + // Suppress "Value stored to ... is never read" analyzer warnings.
>> + //
>> + (VOID)DeviceUDmaMode;
>> +
>> //
>> // Check whether the WORD 88 (supported UltraDMA by drive) is valid
>> //
>> if ((IdentifyData->AtaData.field_validity & 0x04) == 0x00) {
>> return EFI_UNSUPPORTED;
>> }
>>
>> DeviceUDmaMode = IdentifyData->AtaData.ultra_dma_mode;
>> diff --git a/OvmfPkg/VirtioGpuDxe/Gop.c b/OvmfPkg/VirtioGpuDxe/Gop.c
>> index 0b2659d1d2b9..d0f81c349f73 100644
>> --- a/OvmfPkg/VirtioGpuDxe/Gop.c
>> +++ b/OvmfPkg/VirtioGpuDxe/Gop.c
>> @@ -57,16 +57,22 @@ ReleaseGopResources (
>> // by setting ResourceId=0 for it.
>> //
>> Status = VirtioGpuSetScanout (
>> VgpuGop->ParentBus, // VgpuDev
>> 0, 0, 0, 0, // X, Y, Width, Height
>> 0, // ScanoutId
>> 0 // ResourceId
>> );
>> +
>> + //
>> + // Suppress "Value stored to ... is never read" analyzer warnings.
>> + //
>> + (VOID)Status;
>> +
>> //
>> // HACK BEGINS HERE
>> //
>> // According to the GPU Device section of the VirtIo specification, the
>> // above operation is valid:
>> //
>> // "The driver can use resource_id = 0 to disable a scanout."
>> //
>> diff --git a/OvmfPkg/VirtioNetDxe/SnpReceive.c
>> b/OvmfPkg/VirtioNetDxe/SnpReceive.c
>> index cdee9a2aee47..51b2f8a4e370 100644
>> --- a/OvmfPkg/VirtioNetDxe/SnpReceive.c
>> +++ b/OvmfPkg/VirtioNetDxe/SnpReceive.c
>> @@ -153,16 +153,21 @@ VirtioNetReceive (
>> }
>> RxPtr += SIZE_OF_VNET (Mac);
>>
>> if (Protocol != NULL) {
>> *Protocol = (UINT16) ((RxPtr[0] << 8) | RxPtr[1]);
>> }
>> RxPtr += sizeof (UINT16);
>>
>> + //
>> + // Suppress "Value stored to ... is never read" analyzer warnings.
>> + //
>> + (VOID)RxPtr;
>> +
>> Status = EFI_SUCCESS;
>>
>> RecycleDesc:
>> ++Dev->RxLastUsed;
>>
>> //
>> // virtio-0.9.5, 2.4.1 Supplying Buffers to The Device
>> //
>> --
>> 2.19.1.3.g30247aa5d201
>>
>>
>>
>>
>>
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