Re: [patch] UefiCpuPkg/PiSmmCpuDxeSmm: Add "extern" keyword for "gPatchxxx"

["Kinney, Michael D" <michael.d.kinney@intel.com>]

Laszlo,

I think I would rather see the ECC tool fixed.

Mike

> -----Original Message-----
> From: edk2-devel [mailto:edk2-devel-
> bounces@lists.01.org] On Behalf Of Laszlo Ersek
> Sent: Thursday, April 12, 2018 2:34 AM
> To: Bi, Dandan <dandan.bi@intel.com>; edk2-
> devel@lists.01.org
> Cc: Dong, Eric <eric.dong@intel.com>
> Subject: Re: [edk2] [patch] UefiCpuPkg/PiSmmCpuDxeSmm:
> Add "extern" keyword for "gPatchxxx"
> 
> Hello Dandan,
> 
> On 04/12/18 10:50, Dandan Bi wrote:
> > Background description:
> > In SmmProfileInternal.h, ECC check tool report an
> issue at line 103.
> > Detailed ECC Error info:Variable definition appears
> in header file.
> > Include files should contain only public or only
> private data and
> > cannot contain code or define data variables
> >
> > ECC report similar issues in PiSmmCpuDxeSmm.h.
> >
> > Then we review all the new introduced "gPatchxxx",
> since they have
> > been defined in the nasm file, we can add "extern"
> keyword for them
> > in the C source or header files.
> >
> > Cc: Eric Dong <eric.dong@intel.com>
> > Cc: Laszlo Ersek <lersek@redhat.com>
> > Contributed-under: TianoCore Contribution Agreement
> 1.1
> > Signed-off-by: Dandan Bi <dandan.bi@intel.com>
> > ---
> >  UefiCpuPkg/PiSmmCpuDxeSmm/PiSmmCpuDxeSmm.h     | 8
> ++++----
> >  UefiCpuPkg/PiSmmCpuDxeSmm/SmmProfileInternal.h | 2
> +-
> >  UefiCpuPkg/PiSmmCpuDxeSmm/SmramSaveState.c     | 6
> +++---
> >  UefiCpuPkg/PiSmmCpuDxeSmm/X64/Semaphore.c      | 4
> ++--
> >  4 files changed, 10 insertions(+), 10 deletions(-)
> 
> This is a bug (a false positive) in the ECC tool. The
> following
> declaration:
> 
> > X86_ASSEMBLY_PATCH_LABEL            gPatchSmmCr0;
> 
> does not declare an *object* (a variable). Instead, it
> declares a
> *function* (and not a pointer to a function!), because
> (from
> "MdePkg/Include/Library/BaseLib.h"):
> 
> > ///
> > /// Type definition for representing labels in NASM
> source code that allow for
> > /// the patching of immediate operands of IA32 and
> X64 instructions.
> > ///
> > /// While the type is technically defined as a
> function type (note: not a
> > /// pointer-to-function type), such labels in NASM
> source code never stand for
> > /// actual functions, and identifiers declared with
> this function type should
> > /// never be called. This is also why the EFIAPI
> calling convention specifier
> > /// is missing from the typedef, and why the typedef
> does not follow the usual
> > /// edk2 coding style for function (or pointer-to-
> function) typedefs. The VOID
> > /// return type and the VOID argument list are merely
> artifacts.
> > ///
> > typedef VOID (X86_ASSEMBLY_PATCH_LABEL) (VOID);
> 
> That is, when you see
> 
> > X86_ASSEMBLY_PATCH_LABEL            gPatchSmmCr0;
> 
> That is identical to the following function
> declaration:
> 
> > VOID gPatchSmmCr0 (VOID);
> 
> Now, the ISO C99 standard says:
> 
> > 6.2.2 Linkages of identifiers
> >
> > [...]
> >
> >   5 If the declaration of an identifier for a
> function has no
> >     storage-class specifier, its linkage is
> determined exactly as if
> >     it were declared with the storage-class specifier
> /extern/. [...]
> 
> Thus, the report from ECC is a false positive.
> 
> I don't mind the patch (the changes don't make any
> difference at the
> C-language level, see the spec above); however, the
> commit message
> should be 100% clear that the patch works around a
> limitation with the
> ECC tool.
> 
> Can you please submit v2 with an updated commit
> message?
> 
> Thanks!
> Laszlo
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