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

[Madhavan Srinivasan <maddy@linux.ibm.com>]

On 8/6/24 12:24 PM, Christophe Leroy wrote:
>
>
> 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@ellerman.id.au>
>> Signed-off-by: Madhavan Srinivasan <maddy@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.


ok sure and something like this will help?


+        : "r0", "r3" //clobber registers, r0 - syscall number, r3 - 
exit value

Maddy


>
> Christophe
>
>>   }