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141 lines
5.8 KiB
Diff
141 lines
5.8 KiB
Diff
From 0eace4ea9ea42412d4d6a16d24a8660642e41173 Mon Sep 17 00:00:00 2001
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From: Radoslaw Zarzynski <rzarzyns@redhat.com>
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Date: Wed, 24 Jan 2024 17:22:44 +0000
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Subject: [PATCH] common/dout: fix FTBFS on GCC 14
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MIME-Version: 1.0
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Content-Type: text/plain; charset=UTF-8
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Content-Transfer-Encoding: 8bit
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The following problem has been reported by Kaleb Keithley:
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```
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/builddir/build/BUILD/ceph-18.2.1/src/osd/osd_types.h: In lambda function:
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/builddir/build/BUILD/ceph-18.2.1/src/common/dout.h:184:73: error: call to non-‘constexpr’ function ‘virtual unsigned int DoutPrefixProvider::get_subsys() const’
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184 | dout_impl(pdpp->get_cct(), ceph::dout::need_dynamic(pdpp->get_subsys()), v) \
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| ~~~~~~~~~~~~~~~~^~
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/builddir/build/BUILD/ceph-18.2.1/src/common/dout.h:155:58: note: in definition of macro ‘dout_impl’
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155 | return (cctX->_conf->subsys.template should_gather<sub, v>()); \
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| ^~~
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/builddir/build/BUILD/ceph-18.2.1/src/osd/osd_types.h:3617:3: note: in expansion of macro ‘ldpp_dout’
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3617 | ldpp_dout(dpp, 10) << "build_prior all_probe " << all_probe << dendl;
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| ^~~~~~~~~
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```
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For details of the problem and the idea behind the fix,
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please refer to the comment this commit brings to `dout.h`.
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The minimized replicator that the facilitated Goldbot-based
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investigation:
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```cpp
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namespace ceph::dout {
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template<typename T>
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struct dynamic_marker_t {
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T value;
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// constexpr ctor isn't needed as it's an aggregate type
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constexpr operator T() const { return value; }
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};
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template<typename T>
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constexpr dynamic_marker_t<T> need_dynamic(T&& t) {
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return dynamic_marker_t<T>{ std::forward<T>(t) };
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}
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template<typename T>
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struct is_dynamic : public std::false_type {};
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template<typename T>
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struct is_dynamic<dynamic_marker_t<T>> : public std::true_type {};
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} // ceph::dout
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struct subsys_t {
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template <unsigned SubV, int LvlV>
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bool should_gather() const {
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return true;
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}
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bool should_gather(const unsigned sub, int level) const {
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return false;
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}
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};
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static subsys_t subsys;
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do { \
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const bool should_gather = [&](const auto cctX) { \
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if constexpr (ceph::dout::is_dynamic<decltype(sub)>::value || \
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ceph::dout::is_dynamic<decltype(v)>::value) { \
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std::cout << "the dynamic path" << std::endl; \
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return subsys.should_gather(sub, v); \
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} else { \
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/* The parentheses are **essential** because commas in angle \
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* brackets are NOT ignored on macro expansion! A language's \
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* limitation, sorry. */ \
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std::cout << "the static path" << std::endl; \
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/*return subsys.should_gather(sub, v);*/ \
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return (subsys.template should_gather<sub, v>()); \
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} \
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}(cct); \
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} while (0)
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if (decltype(auto) pdpp = (dpp); pdpp) /* workaround -Wnonnull-compare for 'this' */ \
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dout_impl(42, sub, v)
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if (decltype(auto) pdpp = (dpp); pdpp) /* workaround -Wnonnull-compare for 'this' */ \
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dout_impl(42, ceph::dout::need_dynamic(42), v)
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int main() {
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std::random_device dev;
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std::mt19937 rng(dev());
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std::uniform_int_distribution<std::mt19937::result_type> dist6(1,6); // distribution in range [1, 6]
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int sub = dist6(rng);
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ldpp_dout("mocked out", sub);
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//ldpp_subdout("mocked out", 4, 3);
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}
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```
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Fixes: https://tracker.ceph.com/issues/64050
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Signed-off-by: Radoslaw Zarzynski <rzarzyns@redhat.com>
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---
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src/common/dout.h | 20 +++++++++++++++-----
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1 file changed, 15 insertions(+), 5 deletions(-)
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diff --git a/src/common/dout.h b/src/common/dout.h
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index 4cd60efff8fef..6516060c5438e 100644
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--- a/src/common/dout.h
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+++ b/src/common/dout.h
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@@ -144,17 +144,27 @@ struct is_dynamic<dynamic_marker_t<T>> : public std::true_type {};
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#else
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#define dout_impl(cct, sub, v) \
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do { \
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- const bool should_gather = [&](const auto cctX) { \
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- if constexpr (ceph::dout::is_dynamic<decltype(sub)>::value || \
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- ceph::dout::is_dynamic<decltype(v)>::value) { \
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+ const bool should_gather = [&](const auto cctX, auto sub_, auto v_) { \
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+ /* The check is performed on `sub_` and `v_` to leverage the C++'s \
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+ * guarantee on _discarding_ one of blocks of `if constexpr`, which \
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+ * includes also the checks for ill-formed code (`should_gather<>` \
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+ * must not be feed with non-const expresions), BUT ONLY within \
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+ * a template (thus the generic lambda) and under the restriction \
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+ * it's dependant on a parameter of this template). \
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+ * GCC prior to v14 was not enforcing these restrictions. */ \
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+ if constexpr (ceph::dout::is_dynamic<decltype(sub_)>::value || \
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+ ceph::dout::is_dynamic<decltype(v_)>::value) { \
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return cctX->_conf->subsys.should_gather(sub, v); \
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} else { \
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+ constexpr auto sub_helper = static_cast<decltype(sub_)>(sub); \
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+ constexpr auto v_helper = static_cast<decltype(v_)>(v); \
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/* The parentheses are **essential** because commas in angle \
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* brackets are NOT ignored on macro expansion! A language's \
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* limitation, sorry. */ \
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- return (cctX->_conf->subsys.template should_gather<sub, v>()); \
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+ return (cctX->_conf->subsys.template should_gather<sub_helper, \
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+ v_helper>()); \
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} \
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- }(cct); \
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+ }(cct, sub, v); \
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\
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if (should_gather) { \
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ceph::logging::MutableEntry _dout_e(v, sub); \
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