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

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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@xxxxxxxxxxxxxx>
Signed-off-by: Madhavan Srinivasan <maddy@xxxxxxxxxxxxx>
---
  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

  }




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