Re: [PATCH] Makefile: Unset stack-protector gcc flag if it is not supported

[Markos Chandras]

On 02/20/2014 12:53 PM, Richard Weinberger wrote:
> On Thu, Feb 20, 2014 at 1:46 PM, Markos Chandras
> <Markos.Chandras@xxxxxxxxxx> wrote:
> > On 02/07/2014 05:15 PM, Markos Chandras wrote:
> > > In case the compiler does not support the stack-protector option,
> > > unset the flag to avoid build failures. Printing a warning is enough
> > > to let the user know that this flag will not be used.
> > > Fixes the following build problem when using a toolchain which does
> > > not support the -fstack-protector-strong flag:
> > >
> > > Makefile:614: Cannot use CONFIG_CC_STACKPROTECTOR_STRONG:
> > > -fstack-protector-strong not supported by compiler
> > > mips-linux-gnu-gcc: error: unrecognized command line option
> > > '-fstack-protector-strong'
> > > scripts/Makefile.build:308: recipe for target 'scripts/mod/empty.o' failed
> > > make[2]: *** [scripts/mod/empty.o] Error 1
> > > make[2]: *** Waiting for unfinished jobs....
> > > scripts/Makefile.build:455: recipe for target 'scripts/mod' failed
> > >
> > > Cc: Michal Marek <mmarek@xxxxxxx>
> > > Cc: linux-kbuild@xxxxxxxxxxxxxxx
> > > Signed-off-by: Markos Chandras <markos.chandras@xxxxxxxxxx>
> > > ---
> > >    Makefile | 2 ++
> > >    1 file changed, 2 insertions(+)
> > >
> > > diff --git a/Makefile b/Makefile
> > > index 606ef7c..63a5333 100644
> > > --- a/Makefile
> > > +++ b/Makefile
> > > @@ -607,12 +607,14 @@ ifdef CONFIG_CC_STACKPROTECTOR_REGULAR
> > >      ifeq ($(call cc-option, $(stackp-flag)),)
> > >        $(warning Cannot use CONFIG_CC_STACKPROTECTOR: \
> > >                -fstack-protector not supported by compiler))
> > > +    stackp-flag :=
> > >      endif
> > >    else ifdef CONFIG_CC_STACKPROTECTOR_STRONG
> > >      stackp-flag := -fstack-protector-strong
> > >      ifeq ($(call cc-option, $(stackp-flag)),)
> > >        $(warning Cannot use CONFIG_CC_STACKPROTECTOR_STRONG: \
> > >                -fstack-protector-strong not supported by compiler)
> > > +    stackp-flag :=
> > >      endif
> > >    else
> > >      # Force off for distro compilers that enable stack protector by
> > > default.
> >
> > Ping again?
>
> This is by design. We want the build fail if
> CONFIG_CC_STACKPROTECTOR_STRONG is set
> but the toolchain does not support it.
> Otherwise we could end up with a kernel without stackprotector even if
> the config symbol is set.

Hi Richard,

Then maybe the $(warning...) should be converted to $(error...)?
Because it's not really a warning if the build failure is expected to 
happen.

--
markos

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