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

[Christophe Leroy]

Le 09/08/2024 à 06:25, Madhavan Srinivasan a écrit :
> 
> 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 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.
> 
> 
> ok sure and something like this will help?
> 
> 
> +        : "r0", "r3" //clobber registers, r0 - syscall number, r3 - 
> exit value
> 

Not really.

sc will clobber r0 and r3-r12, also SO bit in CR.

Here the reason why you have no problem with that is that SYS_exit never 
returns. At the end, even your "r0" and "r3" clobber are unnecessary 
because of that.

Christophe