[PATCH 03/16] x86, mpx: trace #BR exceptions

[Dave Hansen]

From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

This is the first in a series of MPX tracing patches.
I've found these extremely useful in the process of
debugging applications and the kernel code itself.

This exception hooks in to the bounds (#BR) exception
very early and allows capturing the key registers which
would influence how the exception is handled.

Note that bndcfgu/bndstatus are technically still
64-bit registers even in 32-bit mode.

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
---

 b/arch/x86/include/asm/trace/mpx.h |   48 +++++++++++++++++++++++++++++++++++++
 b/arch/x86/kernel/traps.c          |    2 +
 b/arch/x86/mm/mpx.c                |    3 ++
 3 files changed, 53 insertions(+)

diff -puN /dev/null arch/x86/include/asm/trace/mpx.h
--- /dev/null	2014-10-10 16:10:57.316716958 -0700
+++ b/arch/x86/include/asm/trace/mpx.h	2015-03-31 16:41:56.396286964 -0700
@@ -0,0 +1,48 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM mpx
+
+#if !defined(_TRACE_MPX_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_MPX_H
+
+#include <linux/tracepoint.h>
+
+#ifdef CONFIG_X86_INTEL_MPX
+
+TRACE_EVENT(bounds_exception_mpx,
+
+	TP_PROTO(struct bndcsr *bndcsr),
+	TP_ARGS(bndcsr),
+
+	TP_STRUCT__entry(
+		__field(u64, bndcfgu)
+		__field(u64, bndstatus)
+	),
+
+	TP_fast_assign(
+		__entry->bndcfgu   = bndcsr->bndcfgu;
+		__entry->bndstatus = bndcsr->bndstatus;
+	),
+
+	TP_printk("bndcfgu:0x%llx bndstatus:0x%llx",
+		__entry->bndcfgu,
+		__entry->bndstatus)
+);
+
+#else
+
+/*
+ * This gets used outside of MPX-specific code, so we need a stub.
+ */
+static inline void trace_bounds_exception_mpx(struct bndcsr *bndcsr)
+{
+}
+
+#endif /* CONFIG_X86_INTEL_MPX */
+
+#undef TRACE_INCLUDE_PATH
+#define TRACE_INCLUDE_PATH asm/trace/
+#define TRACE_INCLUDE_FILE mpx
+#endif /* _TRACE_MPX_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff -puN arch/x86/kernel/traps.c~x86-br-exception-trace arch/x86/kernel/traps.c
--- a/arch/x86/kernel/traps.c~x86-br-exception-trace	2015-03-31 16:41:56.391286739 -0700
+++ b/arch/x86/kernel/traps.c	2015-03-31 16:41:56.396286964 -0700
@@ -61,6 +61,7 @@
 #include <asm/mach_traps.h>
 #include <asm/alternative.h>
 #include <asm/mpx.h>
+#include <asm/trace/mpx.h>
 #include <asm/xsave.h>
 
 #ifdef CONFIG_X86_64
@@ -401,6 +402,7 @@ dotraplinkage void do_bounds(struct pt_r
 	if (!bndcsr)
 		goto exit_trap;
 
+	trace_bounds_exception_mpx(bndcsr);
 	/*
 	 * The error code field of the BNDSTATUS register communicates status
 	 * information of a bound range exception #BR or operation involving
diff -puN arch/x86/mm/mpx.c~x86-br-exception-trace arch/x86/mm/mpx.c
--- a/arch/x86/mm/mpx.c~x86-br-exception-trace	2015-03-31 16:41:56.393286830 -0700
+++ b/arch/x86/mm/mpx.c	2015-03-31 16:41:56.397287010 -0700
@@ -18,6 +18,9 @@
 #include <asm/processor.h>
 #include <asm/fpu-internal.h>
 
+#define CREATE_TRACE_POINTS
+#include <asm/trace/mpx.h>
+
 static const char *mpx_mapping_name(struct vm_area_struct *vma)
 {
 	return "[mpx]";
_
--
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