From 7e0bd9ea7e27243661a1ca0291f59ff6c95e692d Mon Sep 17 00:00:00 2001 From: Simon Marchi Date: Wed, 4 Jan 2023 16:15:02 -0500 Subject: [PATCH] gdbsupport: fix scoped_debug_start_end's move constructor I spotted a problem with scoped_debug_start_end's move constructor. When constructing a scoped_debug_start_end through it, it doesn't disable the moved-from object, meaning there are now two objects that will do the side-effects of decrementing the debug_print_depth global and printing the "end" message. Decrementing the debug_print_depth global twice is actually problematic, because the increments and decrements get out of sync, meaning we should hit this assertion, in theory: gdb_assert (debug_print_depth > 0); However, in practice, we don't see that. This is because despite the move constructor being required for this to compile: template static inline scoped_debug_start_end ATTRIBUTE_NULL_PRINTF (6, 7) make_scoped_debug_start_end (PT &&pred, const char *module, const char *func, const char *start_prefix, const char *end_prefix, const char *fmt, ...) { va_list args; va_start (args, fmt); auto res = scoped_debug_start_end (pred, module, func, start_prefix, end_prefix, fmt, args); va_end (args); return res; } ... it is never actually called, because compilers elide the move constructors all the way (the scoped_debug_start_end gets constructed directly in the instance of the top-level caller). To confirm this, I built GDB with -fno-elide-constructors, and now I see it: /home/simark/src/binutils-gdb/gdb/../gdbsupport/common-debug.h:147: internal-error: ~scoped_debug_start_end: Assertion `debug_print_depth > 0' failed. #9 0x00005614ba5f17c3 in internal_error_loc (file=0x5614b8749960 "/home/simark/src/binutils-gdb/gdb/../gdbsupport/common-debug.h", line=147, fmt=0x5614b8733fa0 "%s: Assertion `%s' failed.") at /home/simark/src/binutils-gdb/gdbsupport/errors.cc:58 #10 0x00005614b8e1b2e5 in scoped_debug_start_end::~scoped_debug_start_end (this=0x7ffc6c5e7b40, __in_chrg=) at /home/simark/src/binutils-gdb/gdb/../gdbsupport/common-debug.h:147 #11 0x00005614b96dbe34 in make_scoped_debug_start_end (pred=@0x5614baad7200: true, module=0x5614b891d840 "infrun", func=0x5614b891d800 "infrun_debug_show_threads", start_prefix=0x5614b891d7c0 "enter", end_prefix=0x5614b891d780 "exit", fmt=0x0) at /home/simark/src/binutils-gdb/gdb/../gdbsupport/common-debug.h:235 Fix this by adding an m_disabled field to scoped_debug_start_end, and setting it in the move constructor. Change-Id: Ie5213269c584837f751d2d11de831f45ae4a899f --- gdbsupport/common-debug.h | 21 ++++++++++++++++++++- 1 file changed, 20 insertions(+), 1 deletion(-) diff --git a/gdbsupport/common-debug.h b/gdbsupport/common-debug.h index ec36d88fdea..33b15a005f1 100644 --- a/gdbsupport/common-debug.h +++ b/gdbsupport/common-debug.h @@ -138,10 +138,25 @@ struct scoped_debug_start_end DISABLE_COPY_AND_ASSIGN (scoped_debug_start_end); - scoped_debug_start_end (scoped_debug_start_end &&other) = default; + scoped_debug_start_end (scoped_debug_start_end &&other) + : m_debug_enabled (other.m_debug_enabled), + m_module (other.m_module), + m_func (other.m_func), + m_end_prefix (other.m_end_prefix), + m_msg (other.m_msg), + m_with_format (other.m_with_format), + m_must_decrement_print_depth (other.m_must_decrement_print_depth), + m_disabled (other.m_disabled) + { + /* Avoid the moved-from object doing the side-effects in its destructor. */ + other.m_disabled = true; + } ~scoped_debug_start_end () { + if (m_disabled) + return; + if (m_must_decrement_print_depth) { gdb_assert (debug_print_depth > 0); @@ -194,6 +209,10 @@ private: construction but not during destruction, or vice-versa. We want to make sure there are as many increments are there are decrements. */ bool m_must_decrement_print_depth = false; + + /* True if this object was moved from, and the destructor behavior must be + inhibited. */ + bool m_disabled = false; }; /* Implementation of is_debug_enabled when PT is an invokable type. */ -- 2.30.2