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mac: Faster bit testing for EXC_GUARD exception “flavors”

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After e7630628e9c9, I thought “isn’t there a standard library function
for that?” There is!

Change-Id: I284c7fdf8535c4fc53100e80fceb363bf2afee93
Reviewed-on: https://chromium-review.googlesource.com/431856
Reviewed-by: Scott Graham <scottmg@chromium.org>
This commit is contained in:
Mark Mentovai 2017-01-24 13:31:20 -05:00
parent e7630628e9
commit 1e4be91918
1 changed files with 12 additions and 8 deletions
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20
util/mach/exception_types.cc
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@ -20,6 +20,7 @@
#include <errno.h> #include <errno.h>
#include <libproc.h> #include <libproc.h>
#include <kern/exc_resource.h> #include <kern/exc_resource.h>
#include <strings.h>
#include "base/logging.h" #include "base/logging.h"
#include "base/mac/mach_logging.h" #include "base/mac/mach_logging.h"
@ -200,16 +201,19 @@ int32_t ExceptionCodeForMetrics(exception_type_t exception,
// one another. For the purposes of encoding these codes for metrics, // one another. For the purposes of encoding these codes for metrics,
// convert the flavor codes to their corresponding bit shift values. // convert the flavor codes to their corresponding bit shift values.
const uint32_t guard_flavor = (code_0 >> 32) & 0x1fffffff; const uint32_t guard_flavor = (code_0 >> 32) & 0x1fffffff;
uint8_t metrics_guard_flavor = 0xff; const int first_bit = ffs(guard_flavor);
for (int bit = 0; bit < 29; ++bit) { uint8_t metrics_guard_flavor;
const uint32_t test_mask = 1 << bit; if (first_bit) {
if (guard_flavor & test_mask) { metrics_guard_flavor = first_bit - 1;
// Make sure that no other bits are set.
DCHECK_EQ(guard_flavor, test_mask);
metrics_guard_flavor = bit; const uint32_t test_guard_flavor = 1 << metrics_guard_flavor;
break; if (guard_flavor != test_guard_flavor) {
// Another bit is set.
DCHECK_EQ(guard_flavor, test_guard_flavor);
metrics_guard_flavor = 0xff;
} }
} else {
metrics_guard_flavor = 0xff;
} }
metrics_code_0 = (guard_type << 8) | metrics_guard_flavor; metrics_code_0 = (guard_type << 8) | metrics_guard_flavor;