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Date:   Wed, 20 Dec 2017 14:49:53 -0800
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     <linux-snps-arc@...ts.infradead.org>
CC:     <linux-kernel@...r.kernel.org>, Arnd Bergmann <arnd@...db.de>,
        "Vineet Gupta" <Vineet.Gupta1@...opsys.com>
Subject: [PATCH 1/2] ARC: handle gcc generated __builtin_trap()

gcc toggle -fisolate-erroneous-paths-dereference (default at -O2
onwards) isolates faulty code paths such as null pointer access, divide
by zero etc by emitting __builtin_trap()

Newer ARC gcc generates TRAP_S 5 instruction correspondingly which this
patch handles. If user mode, the task is terminated with a SEGV, for
kernel mode die() called after register and stack dump.

Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
---
 arch/arc/kernel/traps.c        | 6 ++++++
 arch/arc/kernel/troubleshoot.c | 3 +++
 2 files changed, 9 insertions(+)

diff --git a/arch/arc/kernel/traps.c b/arch/arc/kernel/traps.c
index bcd7c9fc5d0f..004f4e4a4c10 100644
--- a/arch/arc/kernel/traps.c
+++ b/arch/arc/kernel/traps.c
@@ -83,6 +83,7 @@ DO_ERROR_INFO(SIGILL, "Illegal Insn (or Seq)", insterror_is_error, ILL_ILLOPC)
 DO_ERROR_INFO(SIGBUS, "Invalid Mem Access", __weak do_memory_error, BUS_ADRERR)
 DO_ERROR_INFO(SIGTRAP, "Breakpoint Set", trap_is_brkpt, TRAP_BRKPT)
 DO_ERROR_INFO(SIGBUS, "Misaligned Access", do_misaligned_error, BUS_ADRALN)
+DO_ERROR_INFO(SIGSEGV, "gcc generated __builtin_trap", do_trap5_error, 0)
 
 /*
  * Entry Point for Misaligned Data access Exception, for emulating in software
@@ -115,6 +116,8 @@ void do_machine_check_fault(unsigned long address, struct pt_regs *regs)
  * Thus TRAP_S <n> can be used for specific purpose
  *  -1 used for software breakpointing (gdb)
  *  -2 used by kprobes
+ *  -5 __builtin_trap() generated by gcc (2018.03 onwards) for toggle such as
+ *     -fno-isolate-erroneous-paths-dereference
  */
 void do_non_swi_trap(unsigned long address, struct pt_regs *regs)
 {
@@ -134,6 +137,9 @@ void do_non_swi_trap(unsigned long address, struct pt_regs *regs)
 		kgdb_trap(regs);
 		break;
 
+	case 5:
+		do_trap5_error(address, regs);
+		break;
 	default:
 		break;
 	}
diff --git a/arch/arc/kernel/troubleshoot.c b/arch/arc/kernel/troubleshoot.c
index 7d8c1d6c2f60..6e9a0a9a6a04 100644
--- a/arch/arc/kernel/troubleshoot.c
+++ b/arch/arc/kernel/troubleshoot.c
@@ -163,6 +163,9 @@ static void show_ecr_verbose(struct pt_regs *regs)
 		else
 			pr_cont("Bus Error, check PRM\n");
 #endif
+	} else if (vec == ECR_V_TRAP) {
+		if (regs->ecr_param == 5)
+			pr_cont("gcc generated __builtin_trap\n");
 	} else {
 		pr_cont("Check Programmer's Manual\n");
 	}
-- 
2.7.4

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