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SubjectRe: [PATCH v3 bpf-next 01/14] samples: bpf: makefile: fix HDR_PROBE "echo"
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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.

--
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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