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SubjectRe: [PATCH v3 bpf-next 01/14] samples: bpf: makefile: fix HDR_PROBE "echo"
On Mon, Sep 16, 2019 at 2:35 PM Andreas Schwab <schwab@linux-m68k.org> wrote:
>
> On Sep 16 2019, Andrii Nakryiko <andrii.nakryiko@gmail.com> wrote:
>
> > On Mon, Sep 16, 2019 at 3:59 AM Ivan Khoronzhuk
> > <ivan.khoronzhuk@linaro.org> wrote:
> >>
> >> echo should be replaced with echo -e to handle '\n' correctly, but
> >> instead, replace it with printf as some systems can't handle echo -e.
> >>
> >> Signed-off-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
> >> ---
> >> samples/bpf/Makefile | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
> >> index 1d9be26b4edd..f50ca852c2a8 100644
> >> --- a/samples/bpf/Makefile
> >> +++ b/samples/bpf/Makefile
> >> @@ -201,7 +201,7 @@ endif
> >>
> >> # Don't evaluate probes and warnings if we need to run make recursively
> >> ifneq ($(src),)
> >> -HDR_PROBE := $(shell echo "\#include <linux/types.h>\n struct list_head { int a; }; int main() { return 0; }" | \
> >> +HDR_PROBE := $(shell printf "\#include <linux/types.h>\n struct list_head { int a; }; int main() { return 0; }" | \
> >
> > printf change is fine, but I'm confused about \# at the beginning of
> > the string.
>
> From the NEWS of make 4.3:
>
> * WARNING: Backward-incompatibility!
> Number signs (#) appearing inside a macro reference or function invocation
> no longer introduce comments and should not be escaped with backslashes:
> thus a call such as:
> foo := $(shell echo '#')
> is legal. Previously the number sign needed to be escaped, for example:
> foo := $(shell echo '\#')
> Now this latter will resolve to "\#". If you want to write makefiles
> portable to both versions, assign the number sign to a variable:
> H := \#
> foo := $(shell echo '$H')
> This was claimed to be fixed in 3.81, but wasn't, for some reason.
> To detect this change search for 'nocomment' in the .FEATURES variable.
>
> Andreas.

Oh, subtle... Thanks for explaining!

>
> --
> Andreas Schwab, schwab@linux-m68k.org
> GPG Key fingerprint = 7578 EB47 D4E5 4D69 2510 2552 DF73 E780 A9DA AEC1
> "And now for something completely different."

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