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 <[e-mail]>

arch/tile/include/asm/processor.h

···
 	barrier();
 }
 
-struct siginfo;
-extern void arch_coredump_signal(struct siginfo *, struct pt_regs *);
-#define arch_coredump_signal arch_coredump_signal
-
 /* Info on this processor (see fs/proc/cpuinfo.c) */
 struct seq_operations;
 extern const struct seq_operations cpuinfo_op;
···
 
 /* Data on which physical memory controller corresponds to which NUMA node. */
 extern int node_controller[];
-
-/* Do we dump information to the console when a user application crashes? */
-extern int show_crashinfo;
 
 #if CHIP_HAS_CBOX_HOME_MAP()
 /* Does the heap allocator return hash-for-home pages by default? */

arch/tile/include/asm/signal.h

···
 int restore_sigcontext(struct pt_regs *, struct sigcontext __user *);
 int setup_sigcontext(struct sigcontext __user *, struct pt_regs *);
 void do_signal(struct pt_regs *regs);
+void signal_fault(const char *type, struct pt_regs *,
+		  void __user *frame, int sig);
+void trace_unhandled_signal(const char *type, struct pt_regs *regs,
+			    unsigned long address, int signo);
 #endif
 
 #endif /* _ASM_TILE_SIGNAL_H */

arch/tile/kernel/compat_signal.c

···
 	return 0;
 
 badframe:
-	force_sig(SIGSEGV, current);
+	signal_fault("bad sigreturn frame", regs, frame, 0);
 	return 0;
 }
 
···
 	return 0;
 
 give_sigsegv:
-	force_sigsegv(sig, current);
+	signal_fault("bad setup frame", regs, frame, sig);
 	return -EFAULT;
 }

arch/tile/kernel/signal.c

···
 
 #define _BLOCKABLE (~(sigmask(SIGKILL) | sigmask(SIGSTOP)))
 
-
 SYSCALL_DEFINE3(sigaltstack, const stack_t __user *, uss,
 		stack_t __user *, uoss, 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)
 {
···
 	return 0;
 
 badframe:
-	force_sig(SIGSEGV, current);
+	signal_fault("bad sigreturn frame", regs, frame, 0);
 	return 0;
 }
 
···
 	return 0;
 
 give_sigsegv:
-	force_sigsegv(sig, current);
+	signal_fault("bad setup frame", regs, frame, sig);
 	return -EFAULT;
 }
 
···
 			 struct pt_regs *regs)
 {
 	int ret;
-
 
 	/* Are we from a system call? */
 	if (regs->faultnum == INT_SWINT_1) {
···
 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;
+		}
+	}
 }

arch/tile/kernel/single_step.c

···
 			.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;
 	}
···
 			.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;
 	}

arch/tile/kernel/traps.c

···
 	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);
 }
 

arch/tile/mm/fault.c

···
 
 #include <arch/interrupts.h>
 
-static noinline void force_sig_info_fault(int si_signo, int si_code,
-	unsigned long address, int fault_num, struct task_struct *tsk)
+static noinline void force_sig_info_fault(const char *type, int si_signo,
+					  int si_code, unsigned long address,
+					  int fault_num,
+					  struct task_struct *tsk,
+					  struct pt_regs *regs)
 {
 	siginfo_t info;
 
···
 	info.si_code = si_code;
 	info.si_addr = (void __user *)address;
 	info.si_trapno = fault_num;
+	trace_unhandled_signal(type, regs, address, si_signo);
 	force_sig_info(si_signo, &info, tsk);
 }
 
···
 		struct pt_regs *, regs)
 {
 	if (address >= PAGE_OFFSET)
-		force_sig_info_fault(SIGSEGV, SEGV_MAPERR, address,
-				     INT_DTLB_MISS, current);
+		force_sig_info_fault("atomic segfault", SIGSEGV, SEGV_MAPERR,
+				     address, INT_DTLB_MISS, current, regs);
 	else
-		force_sig_info_fault(SIGBUS, BUS_ADRALN, address,
-				     INT_UNALIGN_DATA, current);
+		force_sig_info_fault("atomic alignment fault", SIGBUS,
+				     BUS_ADRALN, address,
+				     INT_UNALIGN_DATA, current, regs);
 
 	/*
 	 * Adjust pc to point at the actual instruction, which is unusual
···
 		 */
 		local_irq_enable();
 
-		force_sig_info_fault(SIGSEGV, si_code, address,
-				     fault_num, tsk);
+		force_sig_info_fault("segfault", SIGSEGV, si_code, address,
+				     fault_num, tsk, regs);
 		return 0;
 	}
 
···
 	if (is_kernel_mode)
 		goto no_context;
 
-	force_sig_info_fault(SIGBUS, BUS_ADRERR, address, fault_num, tsk);
+	force_sig_info_fault("bus error", SIGBUS, BUS_ADRERR, address,
+			     fault_num, tsk, regs);
 	return 0;
 }
 

kernel/sysctl.c

···
 
 static struct ctl_table debug_table[] = {
 #if defined(CONFIG_X86) || defined(CONFIG_PPC) || defined(CONFIG_SPARC) || \
-    defined(CONFIG_S390)
+    defined(CONFIG_S390) || defined(CONFIG_TILE)
 	{
 		.procname	= "exception-trace",
 		.data		= &show_unhandled_signals,