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QPlugin: change the generic metadata scan to forwards

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The reason it scanned backwards was valid, but unfortunately that
doesn't work if the metadata magic appears in the debug info that comes
after the metadata.

Task-number: QTBUG-67461
Change-Id: I2bbf422288924c198645fffd16a9276767ca2589
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
This commit is contained in:
Thiago Macieira 2021-09-28 18:41:04 -07:00
parent f21522a4b4
commit 2adf444b5e
1 changed files with 9 additions and 29 deletions
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38
src/corelib/plugin/qlibrary.cpp
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@ -41,6 +41,7 @@
#include "qlibrary_p.h" #include "qlibrary_p.h"
#include <q20algorithm.h> #include <q20algorithm.h>
#include <qbytearraymatcher.h>
#include <qdebug.h> #include <qdebug.h>
#include <qendian.h> #include <qendian.h>
#include <qfile.h> #include <qfile.h>
@ -186,38 +187,17 @@ static qsizetype qt_find_pattern(const char *s, qsizetype s_len,
const char *pattern, ulong p_len) const char *pattern, ulong p_len)
{ {
/* /*
we search from the end of the file because on the supported We used to search from the end of the file so we'd skip the code and find
systems, the read-only data/text segments are placed at the end the read-only data that usually follows. Unfortunately, in debug builds,
of the file. HOWEVER, when building with debugging enabled, all the debug sections come after and are usually much bigger than everything
the debug symbols are placed AFTER the data/text segments. else, making this process slower than necessary with debug plugins.
what does this mean? when building in release mode, the search More importantly, the pattern string may exist in the debug information due
is fast because the data we are looking for is at the end of the to it being used in the plugin in the first place.
file... when building in debug mode, the search is slower
because we have to skip over all the debugging symbols first
*/ */
if (!s || !pattern || qsizetype(p_len) > s_len) static const QByteArrayMatcher matcher(QByteArray(pattern, p_len));
return -1; return matcher.indexIn(s, s_len);
size_t i, hs = 0, hp = 0, delta = s_len - p_len;
for (i = 0; i < p_len; ++i) {
hs += s[delta + i];
hp += pattern[i];
}
i = delta;
for (;;) {
if (hs == hp && qstrncmp(s + i, pattern, p_len) == 0)
return i; // can't overflow, by construction
if (i == 0)
break;
--i;
hs -= s[i + p_len];
hs += s[i];
}
return -1;
} }
/* /*