From mboxrd@z Thu Jan 1 00:00:00 1970 From: Thomas De Schampheleire Date: Tue, 8 Jun 2021 15:06:41 +0200 Subject: [Buildroot] [PATCH 1/3] package/gdb: fix gdb 9.2 segfault with Python 3.9 support In-Reply-To: <20210608130644.10909-1-patrickdepinguin@gmail.com> References: <20210608130644.10909-1-patrickdepinguin@gmail.com> Message-ID: <20210608130644.10909-2-patrickdepinguin@gmail.com> List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: buildroot@busybox.net From: Thomas De Schampheleire When enabling Python 3 support in gdb 9.2, gdb segfaults at startup. The issue is tracked back to following upstream gdb commit, present since gdb 10.1. commit c47bae859a5af0d95224d90000df0e529f7c5aa0 Author: Kevin Buettner Date: Wed May 27 20:05:40 2020 -0700 Fix Python3.9 related runtime problems [...] Backport this commit to 9.2 in Buildroot. Signed-off-by: Thomas De Schampheleire --- ...x-Python3.9-related-runtime-problems.patch | 227 ++++++++++++++++++ 1 file changed, 227 insertions(+) create mode 100644 package/gdb/9.2/0007-Fix-Python3.9-related-runtime-problems.patch diff --git a/package/gdb/9.2/0007-Fix-Python3.9-related-runtime-problems.patch b/package/gdb/9.2/0007-Fix-Python3.9-related-runtime-problems.patch new file mode 100644 index 0000000000..89b0cdc4a0 --- /dev/null +++ b/package/gdb/9.2/0007-Fix-Python3.9-related-runtime-problems.patch @@ -0,0 +1,227 @@ +From c47bae859a5af0d95224d90000df0e529f7c5aa0 Mon Sep 17 00:00:00 2001 +From: Kevin Buettner +Date: Wed, 27 May 2020 20:05:40 -0700 +Subject: [PATCH] Fix Python3.9 related runtime problems + +Python3.9b1 is now available on Rawhide. GDB w/ Python 3.9 support +can be built using the configure switch -with-python=/usr/bin/python3.9. + +Attempting to run gdb/Python3.9 segfaults on startup: + + #0 0x00007ffff7b0582c in PyEval_ReleaseLock () from /lib64/libpython3.9.so.1.0 + #1 0x000000000069ccbf in do_start_initialization () + at worktree-test1/gdb/python/python.c:1789 + #2 _initialize_python () + at worktree-test1/gdb/python/python.c:1877 + #3 0x00000000007afb0a in initialize_all_files () at init.c:237 + ... + +Consulting the the documentation... + +https://docs.python.org/3/c-api/init.html + +...we find that PyEval_ReleaseLock() has been deprecated since version +3.2. It recommends using PyEval_SaveThread or PyEval_ReleaseThread() +instead. In do_start_initialization, in gdb/python/python.c, we +can replace the calls to PyThreadState_Swap() and PyEval_ReleaseLock() +with a single call to PyEval_SaveThread. (Thanks to Keith Seitz +for working this out.) + +With that in place, GDB gets a little bit further. It still dies +on startup, but the backtrace is different: + + #0 0x00007ffff7b04306 in PyOS_InterruptOccurred () + from /lib64/libpython3.9.so.1.0 + #1 0x0000000000576e86 in check_quit_flag () + at worktree-test1/gdb/extension.c:776 + #2 0x0000000000576f8a in set_active_ext_lang (now_active=now_active at entry=0x983c00 ) + at worktree-test1/gdb/extension.c:705 + #3 0x000000000069d399 in gdbpy_enter::gdbpy_enter (this=0x7fffffffd2d0, + gdbarch=0x0, language=0x0) + at worktree-test1/gdb/python/python.c:211 + #4 0x0000000000686e00 in python_new_inferior (inf=0xddeb10) + at worktree-test1/gdb/python/py-inferior.c:251 + #5 0x00000000005d9fb9 in std::function::operator()(inferior*) const (__args#0=, this=0xccad20) + at /usr/include/c++/10/bits/std_function.h:617 + #6 gdb::observers::observable::notify (args#0=0xddeb10, + this=) + at worktree-test1/gdb/../gdbsupport/observable.h:106 + #7 add_inferior_silent (pid=0) + at worktree-test1/gdb/inferior.c:113 + #8 0x00000000005dbcb8 in initialize_inferiors () + at worktree-test1/gdb/inferior.c:947 + ... + +We checked with some Python Developers and were told that we should +acquire the GIL prior to calling any Python C API function. We +definitely don't have the GIL for calls of PyOS_InterruptOccurred(). + +I moved class_gdbpy_gil earlier in the file and use it in +gdbpy_check_quit_flag() to acquire (and automatically release) the +GIL. + +With those changes in place, I was able to run to a GDB prompt. But, +when trying to quit, it segfaulted again due to due to some other +problems with gdbpy_check_quit_flag(): + + Thread 1 "gdb" received signal SIGSEGV, Segmentation fault. + 0x00007ffff7bbab0c in new_threadstate () from /lib64/libpython3.9.so.1.0 + (top-gdb) bt 8 + #0 0x00007ffff7bbab0c in new_threadstate () from /lib64/libpython3.9.so.1.0 + #1 0x00007ffff7afa5ea in PyGILState_Ensure.cold () + from /lib64/libpython3.9.so.1.0 + #2 0x000000000069b58c in gdbpy_gil::gdbpy_gil (this=) + at worktree-test1/gdb/python/python.c:278 + #3 gdbpy_check_quit_flag (extlang=) + at worktree-test1/gdb/python/python.c:278 + #4 0x0000000000576e96 in check_quit_flag () + at worktree-test1/gdb/extension.c:776 + #5 0x000000000057700c in restore_active_ext_lang (previous=0xe9c050) + at worktree-test1/gdb/extension.c:729 + #6 0x000000000088913a in do_my_cleanups ( + pmy_chain=0xc31870 , + old_chain=0xae5720 ) + at worktree-test1/gdbsupport/cleanups.cc:131 + #7 do_final_cleanups () + at worktree-test1/gdbsupport/cleanups.cc:143 + +In this case, we're trying to call a Python C API function after +Py_Finalize() has been called from finalize_python(). I made +finalize_python set gdb_python_initialized to false and then cause +check_quit_flag() to return early when it's false. + +With these changes in place, GDB seems to be working again with +Python3.9b1. I think it likely that there are other problems lurking. +I wouldn't be surprised to find that there are other calls into Python +where we don't first make sure that we have the GIL. Further changes +may well be needed. + +I see no regressions testing on Rawhide using a GDB built with the +default Python version (3.8.3) versus one built using Python 3.9b1. + +I've also tested on Fedora 28, 29, 30, 31, and 32 (all x86_64) using +the default (though updated) system installed versions of Python on +those OSes. This means that I've tested against Python versions +2.7.15, 2.7.17, 2.7.18, 3.7.7, 3.8.2, and 3.8.3. In each case GDB +still builds without problem and shows no regressions after applying +this patch. + +gdb/ChangeLog: + +2020-MM-DD Kevin Buettner + Keith Seitz + + * python/python.c (do_start_initialization): For Python 3.9 and + later, call PyEval_SaveThread instead of PyEval_ReleaseLock. + (class gdbpy_gil): Move to earlier in file. + (finalize_python): Set gdb_python_initialized. + (gdbpy_check_quit_flag): Acquire GIL via gdbpy_gil. Return early + when not initialized. + + +[import into Buildroot, removing ChangeLog change to avoid conflict] +Signed-off-by: Thomas De Schampheleire + +--- + gdb/ChangeLog | 10 ++++++++ + gdb/python/python.c | 56 ++++++++++++++++++++++++--------------------- + 2 files changed, 40 insertions(+), 26 deletions(-) + +diff --git a/gdb/python/python.c b/gdb/python/python.c +index 67f362b852d..4bdd2201abc 100644 +--- a/gdb/python/python.c ++++ b/gdb/python/python.c +@@ -238,6 +238,30 @@ gdbpy_enter::~gdbpy_enter () + PyGILState_Release (m_state); + } + ++/* A helper class to save and restore the GIL, but without touching ++ the other globals that are handled by gdbpy_enter. */ ++ ++class gdbpy_gil ++{ ++public: ++ ++ gdbpy_gil () ++ : m_state (PyGILState_Ensure ()) ++ { ++ } ++ ++ ~gdbpy_gil () ++ { ++ PyGILState_Release (m_state); ++ } ++ ++ DISABLE_COPY_AND_ASSIGN (gdbpy_gil); ++ ++private: ++ ++ PyGILState_STATE m_state; ++}; ++ + /* Set the quit flag. */ + + static void +@@ -251,6 +275,10 @@ gdbpy_set_quit_flag (const struct extension_language_defn *extlang) + static int + gdbpy_check_quit_flag (const struct extension_language_defn *extlang) + { ++ if (!gdb_python_initialized) ++ return 0; ++ ++ gdbpy_gil gil; + return PyOS_InterruptOccurred (); + } + +@@ -943,30 +971,6 @@ gdbpy_source_script (const struct extension_language_defn *extlang, + + /* Posting and handling events. */ + +-/* A helper class to save and restore the GIL, but without touching +- the other globals that are handled by gdbpy_enter. */ +- +-class gdbpy_gil +-{ +-public: +- +- gdbpy_gil () +- : m_state (PyGILState_Ensure ()) +- { +- } +- +- ~gdbpy_gil () +- { +- PyGILState_Release (m_state); +- } +- +- DISABLE_COPY_AND_ASSIGN (gdbpy_gil); +- +-private: +- +- PyGILState_STATE m_state; +-}; +- + /* A single event. */ + struct gdbpy_event + { +@@ -1616,6 +1620,7 @@ finalize_python (void *ignore) + + Py_Finalize (); + ++ gdb_python_initialized = false; + restore_active_ext_lang (previous_active); + } + +@@ -1785,8 +1790,7 @@ do_start_initialization () + return false; + + /* Release the GIL while gdb runs. */ +- PyThreadState_Swap (NULL); +- PyEval_ReleaseLock (); ++ PyEval_SaveThread (); + + make_final_cleanup (finalize_python, NULL); + +-- +2.26.3 + -- 2.26.3