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@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
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