[PATCH v2] um: Fetch registers only for signals which need them

[anton.ivanov at cambridgegreys.com]

From: Anton Ivanov <anton.ivanov at cambridgegreys.com>

UML userspace fetches siginfo and passes it to signal handlers
in UML. This is needed only for some of the signals, because
key handlers like SIGIO make no use of this variable.

Signed-off-by: Anton Ivanov <anton.ivanov at cambridgegreys.com>
---
 arch/um/os-Linux/skas/process.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/arch/um/os-Linux/skas/process.c b/arch/um/os-Linux/skas/process.c
index 4fb877b99dde..0621d521208e 100644
--- a/arch/um/os-Linux/skas/process.c
+++ b/arch/um/os-Linux/skas/process.c
@@ -400,7 +400,20 @@ void userspace(struct uml_pt_regs *regs, unsigned long *aux_fp_regs)
 		if (WIFSTOPPED(status)) {
 			int sig = WSTOPSIG(status);
 
-			ptrace(PTRACE_GETSIGINFO, pid, 0, (struct siginfo *)&si);
+			/* These signal handlers need the si argument.
+			 * The SIGIO and SIGALARM handlers which constitute the
+			 * majority of invocations, do not use it.
+			 */
+			switch (sig) {
+			case SIGSEGV:
+			case SIGTRAP:
+			case SIGILL:
+			case SIGBUS:
+			case SIGFPE:
+			case SIGWINCH:
+				ptrace(PTRACE_GETSIGINFO, pid, 0, (struct siginfo *)&si);
+				break;
+			}
 
 			switch (sig) {
 			case SIGSEGV:
-- 
2.20.1