@@ -1907,10 +1907,9 @@ path::_M_split_cmpts()
_M_cmpts.type(_Type::_Multi);
_M_cmpts.reserve(_M_cmpts.size() + buf.size());
auto output = _M_cmpts._M_impl->end();
- for (auto& c : buf)
+ for (const auto& c : buf)
{
- auto pos = c.str.data() - _M_pathname.data();
- ::new(output++) _Cmpt(c.str, c.type, pos);
+ ::new(output++) _Cmpt(c.str, c.type, parser.offset(c));
++_M_cmpts._M_impl->_M_size;
}
next = buf.begin();
@@ -1930,9 +1929,8 @@ path::_M_split_cmpts()
auto output = _M_cmpts._M_impl->end();
for (int i = 0; i < n; ++i)
{
- auto c = buf[i];
- auto pos = c.str.data() - _M_pathname.data();
- ::new(output++) _Cmpt(c.str, c.type, pos);
+ const auto& c = buf[i];
+ ::new(output++) _Cmpt(c.str, c.type, parser.offset(c));
++_M_cmpts._M_impl->_M_size;
}
}
@@ -18,7 +18,7 @@
// with this library; see the file COPYING3. If not see
// <http://www.gnu.org/licenses/>.
-// 8.4.9 path decomposition [path.decompose]
+// C++17 30.10.8.4.9 path decomposition [fs.path.decompose]
#include <filesystem>
#include <testsuite_hooks.h>
@@ -64,9 +64,32 @@ test02()
}
}
+void
+test03()
+{
+ const std::string narrow = "there/are/no/wrong/turns/only/unexpected/paths";
+ const path::string_type s(narrow.begin(), narrow.end());
+ const auto s1 = s.substr(0, s.length() - 6); // remove "/paths"
+ const auto s2 = s1.substr(0, s1.length() - 16); // remove "/only/..."
+
+ // PR libstdc++/99805
+ path p = path::string_type(s);
+ auto pp = p.parent_path();
+ VERIFY( pp.native() == s1 );
+ pp = pp.parent_path().parent_path();
+ VERIFY( pp.native() == s2 );
+
+ path from_lval(s);
+ pp = from_lval.parent_path();
+ VERIFY( pp.native() == s1 );
+ pp = pp.parent_path().parent_path();
+ VERIFY( pp.native() == s2 );
+}
+
int
main()
{
test01();
test02();
+ test03();
}
Calling the non-const data() member on a COW string makes it "leaked", possibly resulting in reallocating the string to ensure a unique owner. The path::_M_split_cmpts() member parses its _M_pathname string using string_view objects and then calls _M_pathname.data() to find the offset of each string_view from the start of the string. However because _M_pathname is non-const that will cause a COW string to reallocate if it happens to be shared with another string object. This results in the offsets calculated for each component being wrong (i.e. undefined) because the string views no longer refer to substrings of the _M_pathname member. The fix is to use the parse.offset(c) member which gets the offset safely. The bug only happens for the path(string_type&&) constructor and only for COW strings. When constructed from an lvalue string the string's contents are copied rather than just incrementing the refcount, so there's no reallocation when calling the non-const data() member. The testsuite changes check the lvalue case anyway, because we should probably change the deep copying to just be a refcount increment (by adding a path(const string_type&) constructor or an overload for __effective_range(const string_type&), for COW strings only). libstdc++-v3/ChangeLog: PR libstdc++/99805 * src/c++17/fs_path.cc (path::_M_split_cmpts): Do not call non-const member on _M_pathname, to avoid copy-on-write. * testsuite/27_io/filesystem/path/decompose/parent_path.cc: Check construction from strings that might be shared. Tested powerpc64le-linux (SSO an COW strings). Committed to trunk. This needs to be backported to 9 and 10 too, but after the 10.3 release. commit e06d3f5dd7d0c6b4a20fe813e6ee5addd097f560 Author: Jonathan Wakely <jwakely@redhat.com> Date: Wed Apr 7 16:05:42 2021 libstdc++: Fix filesystem::path construction from COW string [PR 99805] Calling the non-const data() member on a COW string makes it "leaked", possibly resulting in reallocating the string to ensure a unique owner. The path::_M_split_cmpts() member parses its _M_pathname string using string_view objects and then calls _M_pathname.data() to find the offset of each string_view from the start of the string. However because _M_pathname is non-const that will cause a COW string to reallocate if it happens to be shared with another string object. This results in the offsets calculated for each component being wrong (i.e. undefined) because the string views no longer refer to substrings of the _M_pathname member. The fix is to use the parse.offset(c) member which gets the offset safely. The bug only happens for the path(string_type&&) constructor and only for COW strings. When constructed from an lvalue string the string's contents are copied rather than just incrementing the refcount, so there's no reallocation when calling the non-const data() member. The testsuite changes check the lvalue case anyway, because we should probably change the deep copying to just be a refcount increment (by adding a path(const string_type&) constructor or an overload for __effective_range(const string_type&), for COW strings only). libstdc++-v3/ChangeLog: PR libstdc++/99805 * src/c++17/fs_path.cc (path::_M_split_cmpts): Do not call non-const member on _M_pathname, to avoid copy-on-write. * testsuite/27_io/filesystem/path/decompose/parent_path.cc: Check construction from strings that might be shared.