linux-kernel - Re: [PATCH v2] arch/x86: Propagate $(CLANG_FLAGS) to $(REALMODE

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Date:   Wed, 3 Feb 2021 13:24:51 +0100
From:   Sedat Dilek <sedat.dilek@...il.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     John Millikin <jmillikin@...il.com>,
        Nathan Chancellor <natechancellor@...il.com>, hpa@...or.com,
        x86@...nel.org, linux-kernel@...r.kernel.org,
        Clang-Built-Linux ML <clang-built-linux@...glegroups.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        John Millikin <john@...n-millikin.com>
Subject: Re: [PATCH v2] arch/x86: Propagate $(CLANG_FLAGS) to $(REALMODE_FLAGS)

On Wed, Feb 3, 2021 at 1:19 PM Borislav Petkov <bp@...en8.de> wrote:
>
> On Sat, Dec 26, 2020 at 05:41:25PM +0900, John Millikin wrote:
> > When cross-compiling with Clang, the `$(CLANG_FLAGS)' variable
> > contains additional flags needed to build C and assembly sources
> > for the target platform. Normally this variable is automatically
> > included in `$(KBUILD_CFLAGS)' by via the top-level Makefile.
> >
> > The x86 real-mode makefile builds `$(REALMODE_CFLAGS)' from a
> > plain assignment and therefore drops the Clang flags. This causes
> > Clang to not recognize x86-specific assembler directives:
> >
> >   arch/x86/realmode/rm/header.S:36:1: error: unknown directive
> >   .type real_mode_header STT_OBJECT ; .size real_mode_header, .-real_mode_header
> >   ^
> >
> > Explicit propagation of `$(CLANG_FLAGS)' to `$(REALMODE_CFLAGS)',
> > which is inherited by real-mode make rules, fixes cross-compilation
> > with Clang for x86 targets.
> >
> > Relevant flags:
> >
> > * `--target' sets the target architecture when cross-compiling. This
> >   flag must be set for both compilation and assembly (`KBUILD_AFLAGS')
> >   to support architecture-specific assembler directives.
> >
> > * `-no-integrated-as' tells clang to assemble with GNU Assembler
> >   instead of its built-in LLVM assembler. This flag is set by default
> >   unless `LLVM_IAS=1' is set, because the LLVM assembler can't yet
> >   parse certain GNU extensions.
> >
> > Signed-off-by: John Millikin <john@...n-millikin.com>
> > ---
> > Changes in v2:
> >   - Reworded the commit message to highlight that this is for
> >     cross-compilation.
> >   - Removed the `ifdef CONFIG_CC_IS_CLANG' guard.
> >
> >  arch/x86/Makefile | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> > index 7116da3980be..412b849063ec 100644
> > --- a/arch/x86/Makefile
> > +++ b/arch/x86/Makefile
> > @@ -33,6 +33,7 @@ REALMODE_CFLAGS += -ffreestanding
> >  REALMODE_CFLAGS += -fno-stack-protector
>
> This one too:
>
> checking file arch/x86/Makefile
> patch: **** malformed patch at line 62:  REALMODE_CFLAGS += -fno-stack-protector
>

I needed to touch this as it was "malformed" and did not apply cleanly.

If it is not too late, feel free to add my:

Tested-by: Sedat Dilek <sedat.dilek@...il.com>

- Sedat -