[PATCH 08/19] x86, mpx: trace #BR exceptions

Dave Hansen
2015-05-08T18:59:53Z

From: Dave Hansen <dave.hansen@linux.intel.com>

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@linux.intel.com>
---

b/arch/x86/include/asm/trace/mpx.h | 49 +++++++++++++++++++++++++++++++++++++
b/arch/x86/kernel/traps.c | 2 +
b/arch/x86/mm/mpx.c | 3 ++
3 files changed, 54 insertions(+)

diff -puN /dev/null arch/x86/include/asm/trace/mpx.h
--- /dev/null 2015-05-06 22:34:35.845652580 -0700
+++ b/arch/x86/include/asm/trace/mpx.h 2015-05-08 11:46:14.227727631 -0700
@@ -0,0 +1,49 @@
+#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/
+#undef TRACE_INCLUDE_FILE
+#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 2015-05-08 11:46:14.222727406 -0700
+++ b/arch/x86/kernel/traps.c 2015-05-08 11:46:14.228727677 -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
@@ -400,6 +401,7 @@ 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 2015-05-08 11:46:14.224727496 -0700
+++ b/arch/x86/mm/mpx.c 2015-05-08 11:46:14.228727677 -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]";
_