[POWERPC] Add compat handler for PTRACE_GETSIGINFO

Current versions of gdb require a working implementation of
PTRACE_GETSIGINFO for proper watchpoint support.  Since struct siginfo
contains pointers it must be converted when passed to a 32-bit debugger.
Signed-off-by: Andreas Schwab <schwab@suse.de>
Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/ppc32.h

@@ -135,4 +135,6 @@ struct ucontext32 {
 	struct mcontext32	uc_mcontext;
 };
 
+extern int copy_siginfo_to_user32(struct compat_siginfo __user *d, siginfo_t *s);
+
 #endif  /* _PPC64_PPC32_H */

arch/powerpc/kernel/ptrace32.c

@@ -29,12 +29,15 @@
 #include <linux/security.h>
 #include <linux/signal.h>
 #include <linux/compat.h>
+#include <linux/elf.h>
 
 #include <asm/uaccess.h>
 #include <asm/page.h>
 #include <asm/pgtable.h>
 #include <asm/system.h>
 
+#include "ppc32.h"
+
 /*
  * does not yet catch signals sent when the child dies.
  * in exit.c or in signal.c.
@@ -64,6 +67,27 @@ static long compat_ptrace_old(struct task_struct *child, long request,
 	return -EPERM;
 }
 
+static int compat_ptrace_getsiginfo(struct task_struct *child, compat_siginfo_t __user *data)
+{
+	siginfo_t lastinfo;
+	int error = -ESRCH;
+
+	read_lock(&tasklist_lock);
+	if (likely(child->sighand != NULL)) {
+		error = -EINVAL;
+		spin_lock_irq(&child->sighand->siglock);
+		if (likely(child->last_siginfo != NULL)) {
+			lastinfo = *child->last_siginfo;
+			error = 0;
+		}
+		spin_unlock_irq(&child->sighand->siglock);
+	}
+	read_unlock(&tasklist_lock);
+	if (!error)
+		return copy_siginfo_to_user32(data, &lastinfo);
+	return error;
+}
+
 long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
 			compat_ulong_t caddr, compat_ulong_t cdata)
 {
@@ -282,6 +306,9 @@ long compat_arch_ptrace(struct task_struct *child, compat_long_t request,
 			0, PT_REGS_COUNT * sizeof(compat_long_t),
 			compat_ptr(data));
 
+	case PTRACE_GETSIGINFO:
+		return compat_ptrace_getsiginfo(child, compat_ptr(data));
+
 	case PTRACE_GETFPREGS:
 	case PTRACE_SETFPREGS:
 	case PTRACE_GETVRREGS: