[PATCH] x86: optionally show last exception from/to register contents

["Jan Beulich" <jbeulich@novell.com>]

.. when dumping register state. This is particularly useful when gcc
managed to tail-call optimize an indirect call which happens to hit a
NULL (or otherwise invalid) pointer.

Signed-off-by: Jan Beulich <jbeulich@novell.com>

 arch/i386/kernel/cpu/amd.c     |    4 ++++
 arch/i386/kernel/cpu/common.c  |    2 ++
 arch/i386/kernel/cpu/intel.c   |   20 ++++++++++++++------
 arch/i386/kernel/traps.c       |   27 +++++++++++++++++++++++++++
 arch/x86_64/kernel/setup.c     |   23 ++++++++++++++++++-----
 arch/x86_64/kernel/traps.c     |   27 +++++++++++++++++++++++++++
 include/asm-i386/msr-index.h   |    3 +++
 include/asm-i386/processor.h   |    4 ++++
 include/asm-x86_64/processor.h |    3 +++
 9 files changed, 102 insertions(+), 11 deletions(-)

--- linux-2.6.23-rc3/arch/i386/kernel/cpu/amd.c	2007-08-13 08:59:44.000000000 +0200
+++ 2.6.23-rc3-x86-ler/arch/i386/kernel/cpu/amd.c	2007-08-07 10:42:55.000000000 +0200
@@ -238,9 +238,13 @@ static void __cpuinit init_amd(struct cp
 	case 0x10:
 	case 0x11:
 		set_bit(X86_FEATURE_K8, c->x86_capability);
+		if (ler_enabled)
+			__get_cpu_var(ler_msr) = MSR_IA32_LASTINTFROMIP;
 		break;
 	case 6:
 		set_bit(X86_FEATURE_K7, c->x86_capability); 
+		if (ler_enabled)
+			__get_cpu_var(ler_msr) = MSR_IA32_LASTINTFROMIP;
 		break;
 	}
 	if (c->x86 >= 6)
--- linux-2.6.23-rc3/arch/i386/kernel/cpu/common.c	2007-08-13 08:59:44.000000000 +0200
+++ 2.6.23-rc3-x86-ler/arch/i386/kernel/cpu/common.c	2007-08-07 10:42:55.000000000 +0200
@@ -503,6 +503,8 @@ static void __cpuinit identify_cpu(struc
 
 	/* Init Machine Check Exception if available. */
 	mcheck_init(c);
+
+	ler_enable();
 }
 
 void __init identify_boot_cpu(void)
--- linux-2.6.23-rc3/arch/i386/kernel/cpu/intel.c	2007-07-09 01:32:17.000000000 +0200
+++ 2.6.23-rc3-x86-ler/arch/i386/kernel/cpu/intel.c	2007-08-07 10:42:55.000000000 +0200
@@ -188,15 +188,23 @@ static void __cpuinit init_intel(struct 
 	}
 #endif
 
-	if (c->x86 == 15) {
+	switch (c->x86) {
+	case 15:
 		set_bit(X86_FEATURE_P4, c->x86_capability);
 		set_bit(X86_FEATURE_SYNC_RDTSC, c->x86_capability);
-	}
-	if (c->x86 == 6) 
+		if (c->x86_model >= 0x03)
+			set_bit(X86_FEATURE_CONSTANT_TSC, c->x86_capability);
+		if (ler_enabled)
+			__get_cpu_var(ler_msr) = MSR_P4_LER_FROM_LIP;
+		break;
+	case 6:
 		set_bit(X86_FEATURE_P3, c->x86_capability);
-	if ((c->x86 == 0xf && c->x86_model >= 0x03) ||
-		(c->x86 == 0x6 && c->x86_model >= 0x0e))
-		set_bit(X86_FEATURE_CONSTANT_TSC, c->x86_capability);
+		if (c->x86_model >= 0x0e)
+			set_bit(X86_FEATURE_CONSTANT_TSC, c->x86_capability);
+		if (ler_enabled)
+			__get_cpu_var(ler_msr) = MSR_IA32_LASTINTFROMIP;
+		break;
+	}
 
 	if (cpu_has_ds) {
 		unsigned int l1;
--- linux-2.6.23-rc3/arch/i386/kernel/traps.c	2007-08-13 08:59:45.000000000 +0200
+++ 2.6.23-rc3-x86-ler/arch/i386/kernel/traps.c	2007-08-07 10:42:55.000000000 +0200
@@ -321,6 +321,13 @@ void show_registers(struct pt_regs *regs
 		unsigned int code_len = code_bytes;
 		unsigned char c;
 
+		if (__get_cpu_var(ler_msr)) {
+			u32 from, to, hi;
+
+			rdmsr(__get_cpu_var(ler_msr), from, hi);
+			rdmsr(__get_cpu_var(ler_msr) + 1, to, hi);
+			printk("LER: %08x -> %08x\n", from, to);
+		}
 		printk("\n" KERN_EMERG "Stack: ");
 		show_stack_log_lvl(NULL, regs, (unsigned long *)esp, KERN_EMERG);
 
@@ -360,6 +367,18 @@ int is_valid_bugaddr(unsigned long eip)
 	return ud2 == 0x0b0f;
 }
 
+DEFINE_PER_CPU(u32, ler_msr);
+int ler_enabled = 0;
+
+void ler_enable(void) {
+	if (__get_cpu_var(ler_msr)) {
+		u64 debugctl;
+
+		rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
+		wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctl | 1);
+	}
+}
+
 /*
  * This is gone through when something in the kernel has done something bad and
  * is about to be terminated.
@@ -846,6 +865,7 @@ fastcall void __kprobes do_debug(struct 
 	struct task_struct *tsk = current;
 
 	get_debugreg(condition, 6);
+	ler_enable();
 
 	if (notify_die(DIE_DEBUG, "debug", regs, condition, error_code,
 					SIGTRAP) == NOTIFY_STOP)
@@ -1239,3 +1259,10 @@ static int __init code_bytes_setup(char 
 	return 1;
 }
 __setup("code_bytes=", code_bytes_setup);
+
+static int __init ler_setup(char *s)
+{
+	ler_enabled = 1;
+	return 1;
+}
+__setup("ler", ler_setup);
--- linux-2.6.23-rc3/arch/x86_64/kernel/setup.c	2007-08-13 08:59:56.000000000 +0200
+++ 2.6.23-rc3-x86-ler/arch/x86_64/kernel/setup.c	2007-08-07 10:42:55.000000000 +0200
@@ -617,6 +617,9 @@ static void __cpuinit init_amd(struct cp
 	/* Family 10 doesn't support C states in MWAIT so don't use it */
 	if (c->x86 == 0x10 && !force_mwait)
 		clear_bit(X86_FEATURE_MWAIT, &c->x86_capability);
+
+	if (ler_enabled && c->x86 <= 16)
+		__get_cpu_var(ler_msr) = MSR_IA32_LASTINTFROMIP;
 }
 
 static void __cpuinit detect_ht(struct cpuinfo_x86 *c)
@@ -736,13 +739,22 @@ static void __cpuinit init_intel(struct 
 			c->x86_phys_bits = 36;
 	}
 
-	if (c->x86 == 15)
+	switch (c->x86) {
+	case 15:
 		c->x86_cache_alignment = c->x86_clflush_size * 2;
-	if ((c->x86 == 0xf && c->x86_model >= 0x03) ||
-	    (c->x86 == 0x6 && c->x86_model >= 0x0e))
-		set_bit(X86_FEATURE_CONSTANT_TSC, &c->x86_capability);
-	if (c->x86 == 6)
+		if (c->x86_model >= 0x03)
+			set_bit(X86_FEATURE_CONSTANT_TSC, &c->x86_capability);
+		if (ler_enabled)
+			__get_cpu_var(ler_msr) = MSR_P4_LER_FROM_LIP;
+		break;
+	case 6:
+		if (c->x86_model >= 0x0e)
+			set_bit(X86_FEATURE_CONSTANT_TSC, &c->x86_capability);
 		set_bit(X86_FEATURE_REP_GOOD, &c->x86_capability);
+		if (ler_enabled)
+			__get_cpu_var(ler_msr) = MSR_IA32_LASTINTFROMIP;
+		break;
+	}
 	if (c->x86 == 15)
 		set_bit(X86_FEATURE_SYNC_RDTSC, &c->x86_capability);
 	else
@@ -906,6 +918,7 @@ void __cpuinit identify_cpu(struct cpuin
 #ifdef CONFIG_NUMA
 	numa_add_cpu(smp_processor_id());
 #endif
+	ler_enable();
 }
  
 
--- linux-2.6.23-rc3/arch/x86_64/kernel/traps.c	2007-08-13 08:59:56.000000000 +0200
+++ 2.6.23-rc3-x86-ler/arch/x86_64/kernel/traps.c	2007-08-07 10:42:55.000000000 +0200
@@ -426,6 +426,13 @@ void show_registers(struct pt_regs *regs
 	 * time of the fault..
 	 */
 	if (in_kernel) {
+		if (__get_cpu_var(ler_msr)) {
+			u64 from, to;
+
+			rdmsrl(__get_cpu_var(ler_msr), from);
+			rdmsrl(__get_cpu_var(ler_msr) + 1, to);
+			printk("LER: %016Lx -> %016Lx\n", from, to);
+		}
 		printk("Stack: ");
 		_show_stack(NULL, regs, (unsigned long*)rsp);
 
@@ -464,6 +471,18 @@ void out_of_line_bug(void)
 EXPORT_SYMBOL(out_of_line_bug);
 #endif
 
+DEFINE_PER_CPU(u32, ler_msr);
+int ler_enabled = 0;
+
+void ler_enable(void) {
+	if (__get_cpu_var(ler_msr)) {
+		u64 debugctl;
+
+		rdmsrl(MSR_IA32_DEBUGCTLMSR, debugctl);
+		wrmsrl(MSR_IA32_DEBUGCTLMSR, debugctl | 1);
+	}
+}
+
 static DEFINE_SPINLOCK(die_lock);
 static int die_owner = -1;
 static unsigned int die_nest_count;
@@ -849,6 +868,7 @@ asmlinkage void __kprobes do_debug(struc
 	siginfo_t info;
 
 	get_debugreg(condition, 6);
+	ler_enable();
 
 	if (notify_die(DIE_DEBUG, "debug", regs, condition, error_code,
 						SIGTRAP) == NOTIFY_STOP)
@@ -1136,3 +1156,10 @@ static int __init kstack_setup(char *s)
 	return 0;
 }
 early_param("kstack", kstack_setup);
+
+static int __init ler_setup(char *s)
+{
+	ler_enabled = 1;
+	return 1;
+}
+__setup("ler", ler_setup);
--- linux-2.6.23-rc3/include/asm-i386/msr-index.h	2007-07-09 01:32:17.000000000 +0200
+++ 2.6.23-rc3-x86-ler/include/asm-i386/msr-index.h	2007-08-07 10:42:55.000000000 +0200
@@ -63,6 +63,9 @@
 #define MSR_IA32_LASTINTFROMIP		0x000001dd
 #define MSR_IA32_LASTINTTOIP		0x000001de
 
+#define MSR_P4_LER_FROM_LIP 		0x000001d7
+#define MSR_P4_LER_TO_LIP 		0x000001d8
+
 #define MSR_IA32_MC0_CTL		0x00000400
 #define MSR_IA32_MC0_STATUS		0x00000401
 #define MSR_IA32_MC0_ADDR		0x00000402
--- linux-2.6.23-rc3/include/asm-i386/processor.h	2007-08-13 09:01:02.000000000 +0200
+++ 2.6.23-rc3-x86-ler/include/asm-i386/processor.h	2007-08-07 10:42:55.000000000 +0200
@@ -643,6 +643,10 @@ static inline unsigned int cpuid_edx(uns
 	return edx;
 }
 
+DECLARE_PER_CPU(u32, ler_msr);
+extern int ler_enabled;
+void ler_enable(void);
+
 /* generic versions from gas */
 #define GENERIC_NOP1	".byte 0x90\n"
 #define GENERIC_NOP2    	".byte 0x89,0xf6\n"
--- linux-2.6.23-rc3/include/asm-x86_64/processor.h	2007-08-13 09:01:07.000000000 +0200
+++ 2.6.23-rc3-x86-ler/include/asm-x86_64/processor.h	2007-08-07 10:42:55.000000000 +0200
@@ -333,6 +333,9 @@ struct extended_sigtable {
 	struct extended_signature sigs[0];
 };
 
+DECLARE_PER_CPU(u32, ler_msr);
+extern int ler_enabled;
+void ler_enable(void);
 
 #define ASM_NOP1 K8_NOP1
 #define ASM_NOP2 K8_NOP2


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