libgo: fix ptrace syscall hooks into glibc

ptrace is actually declared as a variadic function.  On ppc64le
the ABI requires to the caller to allocate space for the parameters
and allows the caller to modify them.

On ppc64le, depending on how and what version of GCC is used,
it will save to parameter save area.  This happened to clobber
a saved LR, and caused syscall.TestExecPtrace to fail with a timeout
when the tracee segfaults, and waits for the parent process to inspect.

Wrap this function to avoid directly calling glibc's ptrace from go.

Fixes golang/go#36698
Fixes go/92567

Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/254755

1 files changed, 16 insertions, 0 deletions

diff --git a/libgo/runtime/go-varargs.c b/libgo/runtime/go-varargs.c
index 2b186ef..f9270a9 100644
--- a/libgo/runtime/go-varargs.c
+++ b/libgo/runtime/go-varargs.c
@@ -18,6 +18,9 @@
 #ifdef HAVE_SYS_SYSCALL_H
 #include <sys/syscall.h>
 #endif
+#ifdef HAVE_SYS_PTRACE_H
+#include <sys/ptrace.h>
+#endif
 
 /* The syscall package calls C functions.  The Go compiler can not
    represent a C varargs functions.  On some systems it's important
@@ -110,3 +113,16 @@ __go_syscall6(uintptr_t flag, uintptr_t a1, uintptr_t a2, uintptr_t a3,
 }
 
 #endif
+
+#ifdef HAVE_SYS_PTRACE_H
+
+// Despite documented appearances, this is actually implemented as
+// a variadic function within glibc.
+
+long
+__go_ptrace(int request, pid_t pid, uintptr_t addr, uintptr_t data)
+{
+  return ptrace (request, pid, addr, data);
+}
+
+#endif