arch/tile: support signal "exception-trace" hook

This change adds support for /proc/sys/debug/exception-trace to tile.
Like x86 and sparc, by default it is set to "1", generating a one-line
printk whenever a user process crashes.  By setting it to "2", we get
a much more complete userspace diagnostic at crash time, including
a user-space backtrace, register dump, and memory dump around the
address of the crash.

Some vestiges of the Tilera-internal version of this support are
removed with this patch (the show_crashinfo variable and the
arch_coredump_signal function).  We retain a "crashinfo" boot parameter
which allows you to set the boot-time value of exception-trace.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

4 files changed, 131 insertions, 6 deletions

diff --git a/arch/tile/kernel/compat_signal.c b/arch/tile/kernel/compat_signal.c
index dbb0dfc7bece..a7869ad62776 100644
--- a/arch/tile/kernel/compat_signal.c
+++ b/arch/tile/kernel/compat_signal.c
@@ -317,7 +317,7 @@ long compat_sys_rt_sigreturn(struct pt_regs *regs)
         return 0;
 
 badframe:
-        force_sig(SIGSEGV, current);
+        signal_fault("bad sigreturn frame", regs, frame, 0);
         return 0;
 }
 
@@ -431,6 +431,6 @@ int compat_setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
         return 0;
 
 give_sigsegv:
-        force_sigsegv(sig, current);
+        signal_fault("bad setup frame", regs, frame, sig);
         return -EFAULT;
 }
diff --git a/arch/tile/kernel/signal.c b/arch/tile/kernel/signal.c
index 1260321155f1..bedaf4e9f3a7 100644
--- a/arch/tile/kernel/signal.c
+++ b/arch/tile/kernel/signal.c
@@ -39,7 +39,6 @@
 
 #define _BLOCKABLE (~(sigmask(SIGKILL) | sigmask(SIGSTOP)))
 
-
 SYSCALL_DEFINE3(sigaltstack, const stack_t __user *, uss,
                 stack_t __user *, uoss, struct pt_regs *, regs)
 {
@@ -78,6 +77,13 @@ int restore_sigcontext(struct pt_regs *regs,
         return err;
 }
 
+void signal_fault(const char *type, struct pt_regs *regs,
+                  void __user *frame, int sig)
+{
+        trace_unhandled_signal(type, regs, (unsigned long)frame, SIGSEGV);
+        force_sigsegv(sig, current);
+}
+
 /* The assembly shim for this function arranges to ignore the return value. */
 SYSCALL_DEFINE1(rt_sigreturn, struct pt_regs *, regs)
 {
@@ -105,7 +111,7 @@ SYSCALL_DEFINE1(rt_sigreturn, struct pt_regs *, regs)
         return 0;
 
 badframe:
-        force_sig(SIGSEGV, current);
+        signal_fault("bad sigreturn frame", regs, frame, 0);
         return 0;
 }
 
@@ -231,7 +237,7 @@ static int setup_rt_frame(int sig, struct k_sigaction *ka, siginfo_t *info,
         return 0;
 
 give_sigsegv:
-        force_sigsegv(sig, current);
+        signal_fault("bad setup frame", regs, frame, sig);
         return -EFAULT;
 }
 
@@ -245,7 +251,6 @@ static int handle_signal(unsigned long sig, siginfo_t *info,
 {
         int ret;
 
-
         /* Are we from a system call? */
         if (regs->faultnum == INT_SWINT_1) {
                 /* If so, check system call restarting.. */
@@ -363,3 +368,118 @@ done:
         /* Avoid double syscall restart if there are nested signals. */
         regs->faultnum = INT_SWINT_1_SIGRETURN;
 }
+
+int show_unhandled_signals = 1;
+
+static int __init crashinfo(char *str)
+{
+        unsigned long val;
+        const char *word;
+
+        if (*str == '\0')
+                val = 2;
+        else if (*str != '=' || strict_strtoul(++str, 0, &val) != 0)
+                return 0;
+        show_unhandled_signals = val;
+        switch (show_unhandled_signals) {
+        case 0:
+                word = "No";
+                break;
+        case 1:
+                word = "One-line";
+                break;
+        default:
+                word = "Detailed";
+                break;
+        }
+        pr_info("%s crash reports will be generated on the console\n", word);
+        return 1;
+}
+__setup("crashinfo", crashinfo);
+
+static void dump_mem(void __user *address)
+{
+        void __user *addr;
+        enum { region_size = 256, bytes_per_line = 16 };
+        int i, j, k;
+        int found_readable_mem = 0;
+
+        pr_err("\n");
+        if (!access_ok(VERIFY_READ, address, 1)) {
+                pr_err("Not dumping at address 0x%lx (kernel address)\n",
+                       (unsigned long)address);
+                return;
+        }
+
+        addr = (void __user *)
+                (((unsigned long)address & -bytes_per_line) - region_size/2);
+        if (addr > address)
+                addr = NULL;
+        for (i = 0; i < region_size;
+             addr += bytes_per_line, i += bytes_per_line) {
+                unsigned char buf[bytes_per_line];
+                char line[100];
+                if (copy_from_user(buf, addr, bytes_per_line))
+                        continue;
+                if (!found_readable_mem) {
+                        pr_err("Dumping memory around address 0x%lx:\n",
+                               (unsigned long)address);
+                        found_readable_mem = 1;
+                }
+                j = sprintf(line, REGFMT":", (unsigned long)addr);
+                for (k = 0; k < bytes_per_line; ++k)
+                        j += sprintf(&line[j], " %02x", buf[k]);
+                pr_err("%s\n", line);
+        }
+        if (!found_readable_mem)
+                pr_err("No readable memory around address 0x%lx\n",
+                       (unsigned long)address);
+}
+
+void trace_unhandled_signal(const char *type, struct pt_regs *regs,
+                            unsigned long address, int sig)
+{
+        struct task_struct *tsk = current;
+
+        if (show_unhandled_signals == 0)
+                return;
+
+        /* If the signal is handled, don't show it here. */
+        if (!is_global_init(tsk)) {
+                void __user *handler =
+                        tsk->sighand->action[sig-1].sa.sa_handler;
+                if (handler != SIG_IGN && handler != SIG_DFL)
+                        return;
+        }
+
+        /* Rate-limit the one-line output, not the detailed output. */
+        if (show_unhandled_signals <= 1 && !printk_ratelimit())
+                return;
+
+        printk("%s%s[%d]: %s at %lx pc "REGFMT" signal %d",
+               task_pid_nr(tsk) > 1 ? KERN_INFO : KERN_EMERG,
+               tsk->comm, task_pid_nr(tsk), type, address, regs->pc, sig);
+
+        print_vma_addr(KERN_CONT " in ", regs->pc);
+
+        printk(KERN_CONT "\n");
+
+        if (show_unhandled_signals > 1) {
+                switch (sig) {
+                case SIGILL:
+                case SIGFPE:
+                case SIGSEGV:
+                case SIGBUS:
+                        pr_err("User crash: signal %d,"
+                               " trap %ld, address 0x%lx\n",
+                               sig, regs->faultnum, address);
+                        show_regs(regs);
+                        dump_mem((void __user *)address);
+                        break;
+                default:
+                        pr_err("User crash: signal %d, trap %ld\n",
+                               sig, regs->faultnum);
+                        break;
+                }
+        }
+}
diff --git a/arch/tile/kernel/single_step.c b/arch/tile/kernel/single_step.c
index 86df5a239b70..4032ca8e51b6 100644
--- a/arch/tile/kernel/single_step.c
+++ b/arch/tile/kernel/single_step.c
@@ -186,6 +186,8 @@ static tile_bundle_bits rewrite_load_store_unaligned(
                         .si_code = SEGV_MAPERR,
                         .si_addr = addr
                 };
+                trace_unhandled_signal("segfault", regs,
+                                       (unsigned long)addr, SIGSEGV);
                 force_sig_info(info.si_signo, &info, current);
                 return (tile_bundle_bits) 0;
         }
@@ -196,6 +198,8 @@ static tile_bundle_bits rewrite_load_store_unaligned(
                         .si_code = BUS_ADRALN,
                         .si_addr = addr
                 };
+                trace_unhandled_signal("unaligned trap", regs,
+                                       (unsigned long)addr, SIGBUS);
                 force_sig_info(info.si_signo, &info, current);
                 return (tile_bundle_bits) 0;
         }
diff --git a/arch/tile/kernel/traps.c b/arch/tile/kernel/traps.c
index 5474fc2e77e8..f9803dfa7357 100644
--- a/arch/tile/kernel/traps.c
+++ b/arch/tile/kernel/traps.c
@@ -308,6 +308,7 @@ void __kprobes do_trap(struct pt_regs *regs, int fault_num,
         info.si_addr = (void __user *)address;
         if (signo == SIGILL)
                 info.si_trapno = fault_num;
+        trace_unhandled_signal("trap", regs, address, signo);
         force_sig_info(signo, &info, current);
 }