[PATCH] selftest/powerpc/benchmark: remove requirement libc-dev

[Christophe Leroy]

Le 05/08/2024 à 10:30, Madhavan Srinivasan a écrit :
> Currently exec-target.c file is linked as static and this
> post a requirement to install libc dev package to build.
> Without it, build-breaks when compiling selftest/powerpc/benchmark.
> 
>    CC       exec_target
> /usr/bin/ld: cannot find -lc: No such file or directory
> collect2: error: ld returned 1 exit status
> 
> exec_target.c is using "syscall" library function which
> could be replaced with a inline assembly and the same is
> proposed as a fix here.
> 
> Suggested-by: Michael Ellerman <mpe at ellerman.id.au>
> Signed-off-by: Madhavan Srinivasan <maddy at linux.ibm.com>
> ---
>   tools/testing/selftests/powerpc/benchmarks/Makefile    |  2 +-
>   .../testing/selftests/powerpc/benchmarks/exec_target.c | 10 ++++++++--
>   2 files changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/tools/testing/selftests/powerpc/benchmarks/Makefile b/tools/testing/selftests/powerpc/benchmarks/Makefile
> index 1321922038d0..ca4483c238b9 100644
> --- a/tools/testing/selftests/powerpc/benchmarks/Makefile
> +++ b/tools/testing/selftests/powerpc/benchmarks/Makefile
> @@ -18,4 +18,4 @@ $(OUTPUT)/context_switch: LDLIBS += -lpthread
>   
>   $(OUTPUT)/fork: LDLIBS += -lpthread
>   
> -$(OUTPUT)/exec_target: CFLAGS += -static -nostartfiles
> +$(OUTPUT)/exec_target: CFLAGS += -nostartfiles
> diff --git a/tools/testing/selftests/powerpc/benchmarks/exec_target.c b/tools/testing/selftests/powerpc/benchmarks/exec_target.c
> index c14b0fc1edde..20027a23b594 100644
> --- a/tools/testing/selftests/powerpc/benchmarks/exec_target.c
> +++ b/tools/testing/selftests/powerpc/benchmarks/exec_target.c
> @@ -7,10 +7,16 @@
>    */
>   
>   #define _GNU_SOURCE
> -#include <unistd.h>
>   #include <sys/syscall.h>
>   
>   void _start(void)
>   {
> -	syscall(SYS_exit, 0);
> +	asm volatile (
> +		"li %%r0, %[sys_exit];"
> +		"li %%r3, 0;"
> +		"sc;"
> +		:
> +		: [sys_exit] "i" (SYS_exit)
> +		: "r0", "r3"
> +	);

That looks ok because SYS_exit() is not supposed to return, but in the 
general case you should take a lot more precautions regarding which 
registers get clobbered when using sc.

Maybe it is worth a comment.

Christophe

>   }