On 2019-04-15 09:25:33, Laszlo Ersek wrote:
> 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 <[email protected]>
> >> Cc: Ard Biesheuvel <[email protected]>
> >> Cc: Jordan Justen <[email protected]>
> >> Cc: Julien Grall <[email protected]>
> >> 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 <[email protected]>
> >> ---
> >> 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.
I think if the setting can be tweaked, maybe most of these changes
wouldn't be needed. But, it also might prevent you from having to
"fix" similar issues in the future.
> 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!)
In MdePkg/Include/X64/ProcessorBind.h, I see:
//
// Disable ICC's remark #593: "Variable" was set but never used.
// This is legal ANSI C code so we disable the remark that is turned on with /W4
//
#pragma warning ( disable : 593 )
And, then we have -Wno-unused-but-set-variable for GCC.
Regarding "spurious assignments", MdePkg/Include/X64/ProcessorBind.h,
I also see:
//
// This warning is for potentially uninitialized local variable, and it may
cause false
// positive issues in VS2013 and VS2015 build
//
#pragma warning ( disable : 4701 )
-Jordan
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