summaryrefslogtreecommitdiffstats
path: root/courgette
diff options
context:
space:
mode:
authormal@chromium.org <mal@chromium.org@0039d316-1c4b-4281-b951-d872f2087c98>2010-09-26 02:21:47 +0000
committermal@chromium.org <mal@chromium.org@0039d316-1c4b-4281-b951-d872f2087c98>2010-09-26 02:21:47 +0000
commit7f51255c5711efe3cfccebe15e0213364c1273e8 (patch)
treea8bc68def78d0acc9f5b06db8c3264d1bcf41759 /courgette
parentf4580339db115c23098d09545db9c50a83e2e3e2 (diff)
downloadchromium_src-7f51255c5711efe3cfccebe15e0213364c1273e8.zip
chromium_src-7f51255c5711efe3cfccebe15e0213364c1273e8.tar.gz
chromium_src-7f51255c5711efe3cfccebe15e0213364c1273e8.tar.bz2
Prevent Courgette from choosing a really large executable as the basis of comparison for a small executable.
Patch by sra@chromium.org. BUG= none TEST= diff installer creation succeeds. Review URL: http://codereview.chromium.org/3431029 git-svn-id: svn://svn.chromium.org/chrome/trunk/src@60591 0039d316-1c4b-4281-b951-d872f2087c98
Diffstat (limited to 'courgette')
-rw-r--r--courgette/ensemble_create.cc27
1 files changed, 27 insertions, 0 deletions
diff --git a/courgette/ensemble_create.cc b/courgette/ensemble_create.cc
index 00de688..48126e4 100644
--- a/courgette/ensemble_create.cc
+++ b/courgette/ensemble_create.cc
@@ -78,6 +78,30 @@ TransformationPatchGenerator* MakeGenerator(Element* old_element,
}
}
+// Checks to see if the proposed comparison is 'unsafe'. Sometimes one element
+// from 'old' is matched as the closest element to multiple elements from 'new'.
+// Each time this happens, the old element is transformed and serialized. This
+// is a problem when the old element is huge compared with the new element
+// because the mutliple serialized copies can be much bigger than the size of
+// either ensemble.
+//
+// The right way to avoid this is to ensure any one element from 'old' is
+// serialized once, which requires matching code in the patch application.
+//
+// This is a quick hack to avoid the problem by prohibiting a big difference in
+// size between matching elements.
+bool UnsafeDifference(Element* old_element, Element* new_element) {
+ double kMaxBloat = 2.0;
+ size_t kMinWorrysomeDifference = 2 << 20; // 2MB
+ size_t old_size = old_element->region().length();
+ size_t new_size = new_element->region().length();
+ size_t low_size = std::min(old_size, new_size);
+ size_t high_size = std::max(old_size, new_size);
+ if (high_size - low_size < kMinWorrysomeDifference) return false;
+ if (high_size < low_size * kMaxBloat) return false;
+ return true;
+}
+
// FindGenerators finds TransformationPatchGenerators for the elements of
// |new_ensemble|. For each element of |new_ensemble| we find the closest
// matching element from |old_ensemble| and use that as the basis for
@@ -134,6 +158,9 @@ Status FindGenerators(Ensemble* old_ensemble, Ensemble* new_ensemble,
if (old_element->kind() != new_element->kind())
continue;
+ if (UnsafeDifference(old_element, new_element))
+ continue;
+
base::Time start_compare = base::Time::Now();
DifferenceEstimator::Base* old_base = bases[old_index];
size_t difference = difference_estimator.Measure(old_base, new_subject);