um: Move faultinfo extraction into userspace routine

The segv handler is called slightly differently depending on whether
PTRACE_FULL_FAULTINFO is set or not (32bit vs. 64bit). The only
difference is that we don't try to pass the registers and instruction
pointer to the segv handler.

It would be good to either document or remove the difference, but I do
not know why this difference exists. And, passing NULL can even result
in a crash.

Signed-off-by: Benjamin Berg <benjamin@sipsolutions.net>
Link: https://patch.msgid.link/20250602130052.545733-2-benjamin@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Author: benzea

arch/um/os-Linux/skas/process.c

@@ -163,12 +163,6 @@ static void get_skas_faultinfo(int pid, struct faultinfo *fi)
 	memcpy(fi, (void *)current_stub_stack(), sizeof(*fi));
 }
 
-static void handle_segv(int pid, struct uml_pt_regs *regs)
-{
-	get_skas_faultinfo(pid, &regs->faultinfo);
-	segv(regs->faultinfo, 0, 1, NULL, NULL);
-}
-
 static void handle_trap(int pid, struct uml_pt_regs *regs)
 {
 	if ((UPT_IP(regs) >= STUB_START) && (UPT_IP(regs) < STUB_END))
@@ -521,13 +515,14 @@ void userspace(struct uml_pt_regs *regs)
 
 			switch (sig) {
 			case SIGSEGV:
-				if (PTRACE_FULL_FAULTINFO) {
-					get_skas_faultinfo(pid,
-							   &regs->faultinfo);
+				get_skas_faultinfo(pid, &regs->faultinfo);
+
+				if (PTRACE_FULL_FAULTINFO)
 					(*sig_info[SIGSEGV])(SIGSEGV, (struct siginfo *)&si,
 							     regs, NULL);
-				}
-				else handle_segv(pid, regs);
+				else
+					segv(regs->faultinfo, 0, 1, NULL, NULL);
+
 				break;
 			case SIGTRAP + 0x80:
 				handle_trap(pid, regs);