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

3 files changed, 18 insertions, 2 deletions

diff --git a/libgo/go/syscall/libcall_glibc.go b/libgo/go/syscall/libcall_glibc.go
index a90fc9b..823343d 100644
--- a/libgo/go/syscall/libcall_glibc.go
+++ b/libgo/go/syscall/libcall_glibc.go
@@ -32,7 +32,7 @@ func Futimes(fd int, tv []Timeval) (err error) {
 }
 
 //sys	ptrace(request int, pid int, addr uintptr, data uintptr) (err error)
-//ptrace(request _C_int, pid Pid_t, addr *byte, data *byte) _C_long
+//__go_ptrace(request _C_int, pid Pid_t, addr *byte, data *byte) _C_long
 
 //sys	accept4(fd int, sa *RawSockaddrAny, len *Socklen_t, flags int) (nfd int, err error)
 //accept4(fd _C_int, sa *RawSockaddrAny, len *Socklen_t, flags _C_int) _C_int
diff --git a/libgo/go/syscall/libcall_linux.go b/libgo/go/syscall/libcall_linux.go
index 88286c0..78fda0e 100644
--- a/libgo/go/syscall/libcall_linux.go
+++ b/libgo/go/syscall/libcall_linux.go
@@ -11,7 +11,7 @@ import (
 )
 
 //sysnb raw_ptrace(request int, pid int, addr *byte, data *byte) (err Errno)
-//ptrace(request _C_int, pid Pid_t, addr *byte, data *byte) _C_long
+//__go_ptrace(request _C_int, pid Pid_t, addr *byte, data *byte) _C_long
 
 func ptracePeek(req int, pid int, addr uintptr, out []byte) (count int, err error) {
 	// The peek requests are machine-size oriented, so we wrap it
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