uml: kernel segfaults should dump proper registers

If there's a segfault inside the kernel, we want a dump of the registers at
the point of the segfault, not the registers at the point of calling panic or
the last userspace registers.

sig_handler_common_skas now uses a static register set in the case of a
SIGSEGV to avoid messing up the process registers if the segfault turns out to
be non-fatal.

The architecture sigcontext-to-pt_regs copying code was repurposed to copy
data out of the SEGV stack frame.

Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 3 deletions

diff --git a/arch/um/kernel/trap.c b/arch/um/kernel/trap.c
index c3e62e634c0a..0c467fa08870 100644
--- a/arch/um/kernel/trap.c
+++ b/arch/um/kernel/trap.c
@@ -170,8 +170,10 @@ unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
                 flush_tlb_kernel_vm();
                 return 0;
         }
-        else if(current->mm == NULL)
-                panic("Segfault with no mm");
+        else if(current->mm == NULL) {
+                show_regs(container_of(regs, struct pt_regs, regs));
+                panic("Segfault with no mm");
+        }
 
         if (SEGV_IS_FIXABLE(&fi) || SEGV_MAYBE_FIXABLE(&fi))
                 err = handle_page_fault(address, ip, is_write, is_user, &si.si_code);
@@ -194,9 +196,11 @@ unsigned long segv(struct faultinfo fi, unsigned long ip, int is_user,
         else if(!is_user && arch_fixup(ip, regs))
                 return 0;
 
-        if(!is_user)
+        if(!is_user) {
+                show_regs(container_of(regs, struct pt_regs, regs));
                 panic("Kernel mode fault at addr 0x%lx, ip 0x%lx",
                       address, ip);
+        }
 
         if (err == -EACCES) {
                 si.si_signo = SIGBUS;