Re: [PATCH] tools: bpf: Disable stack protector

[Yonghong Song]

On 1/18/23 11:28 AM, Eduard Zingerman wrote:
> On Sat, 2023-01-14 at 18:00 -0500, Peter Foley wrote:
> > Avoid build errors on distros that force the stack protector on by
> > default.
> > e.g.
> >    CLANG   /home/peter/linux/work/tools/bpf/bpftool/pid_iter.bpf.o
> > skeleton/pid_iter.bpf.c:53:5: error: A call to built-in function '__stack_chk_fail' is not supported.
> > int iter(struct bpf_iter__task_file *ctx)
> >      ^
> > 1 error generated.
> >
> > Signed-off-by: Peter Foley <pefoley2@xxxxxxxxxxx>
> > ---
> >   tools/bpf/bpftool/Makefile    | 1 +
> >   tools/bpf/runqslower/Makefile | 5 +++--
> >   2 files changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/tools/bpf/bpftool/Makefile b/tools/bpf/bpftool/Makefile
> > index f610e184ce02a..36ac0002e386f 100644
> > --- a/tools/bpf/bpftool/Makefile
> > +++ b/tools/bpf/bpftool/Makefile
> > @@ -215,6 +215,7 @@ $(OUTPUT)%.bpf.o: skeleton/%.bpf.c $(OUTPUT)vmlinux.h $(LIBBPF_BOOTSTRAP)
> >   		-I$(or $(OUTPUT),.) \
> >   		-I$(srctree)/tools/include/uapi/ \
> >   		-I$(LIBBPF_BOOTSTRAP_INCLUDE) \
> > +		-fno-stack-protector \
>
> While working on clang patch to disable stack protector
> for BPF target I've noticed that there is an option to
> disable default configuration file altogether [1]:
>
>    --no-default-config
>
> Should we consider it instead of -fno-stack-protector
> to shield ourselves from any potential distro-specific
> changes?

Peter, could you help check whether adding --no-default-config works
in your environment or not?

> [1] https://clang.llvm.org/docs/ClangCommandLineReference.html#cmdoption-clang-no-default-config
>
> >   		-g -O2 -Wall -target bpf -c $< -o $@
> >   	$(Q)$(LLVM_STRIP) -g $@
> >   
> > diff --git a/tools/bpf/runqslower/Makefile b/tools/bpf/runqslower/Makefile
> > index 8b3d87b82b7a2..f7313cc966a04 100644
> > --- a/tools/bpf/runqslower/Makefile
> > +++ b/tools/bpf/runqslower/Makefile
> > @@ -60,8 +60,9 @@ $(OUTPUT)/%.skel.h: $(OUTPUT)/%.bpf.o | $(BPFTOOL)
> >   	$(QUIET_GEN)$(BPFTOOL) gen skeleton $< > $@
> >   
> >   $(OUTPUT)/%.bpf.o: %.bpf.c $(BPFOBJ) | $(OUTPUT)
> > -	$(QUIET_GEN)$(CLANG) -g -O2 -target bpf $(INCLUDES)		      \
> > -		 -c $(filter %.c,$^) -o $@ &&				      \
> > +	$(QUIET_GEN)$(CLANG) -g -O2 -target bpf $(INCLUDES)		\
> > +		 -fno-stack-protector 					\
> > +		 -c $(filter %.c,$^) -o $@ &&				\
> >   	$(LLVM_STRIP) -g $@
> >   
> >   $(OUTPUT)/%.o: %.c | $(OUTPUT)
> >
> > ---
> > base-commit: 97ec4d559d939743e8af83628be5af8da610d9dc
> > change-id: 20230114-bpf-918ae127b77a
> >
> > Best regards,