Debugging GNU Emacs
-Copyright (C) 1985, 2000-2011 Free Software Foundation, Inc.
+Copyright (C) 1985, 2000-2014 Free Software Foundation, Inc.
See the end of the file for license conditions.
read the Windows-specific section near the end of this document.]
** When you debug Emacs with GDB, you should start it in the directory
-where the executable was made. That directory has a .gdbinit file
-that defines various "user-defined" commands for debugging Emacs.
-(These commands are described below under "Examining Lisp object
-values" and "Debugging Emacs Redisplay problems".)
-
-** When you are trying to analyze failed assertions, it will be
-essential to compile Emacs either completely without optimizations or
-at least (when using GCC) with the -fno-crossjumping option. Failure
-to do so may make the compiler recycle the same abort call for all
-assertions in a given function, rendering the stack backtrace useless
-for identifying the specific failed assertion.
+where the executable was made (the 'src' directory in the Emacs source
+tree). That directory has a .gdbinit file that defines various
+"user-defined" commands for debugging Emacs. (These commands are
+described below under "Examining Lisp object values" and "Debugging
+Emacs Redisplay problems".)
+
+Some GDB versions by default do not automatically load .gdbinit files
+in the directory where you invoke GDB. With those versions of GDB,
+you will see a warning when GDB starts, like this:
+
+ warning: File ".../src/.gdbinit" auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/auto-load".
+
+There are several ways to overcome that difficulty, they are all
+described in the node "Auto-loading safe path" in the GDB user manual.
+
+** When you are trying to analyze failed assertions or backtraces, it
+is essential to compile Emacs with flags suitable for debugging.
+With GCC 4.8 or later, you can invoke 'make' with CFLAGS="-Og -g3".
+With older GCC or non-GCC compilers, you can use CFLAGS="-O0 -g3".
+With GCC and higher optimization levels such as -O2, the
+-fno-omit-frame-pointer and -fno-crossjumping options are often
+essential. The latter prevents GCC from using the same abort call for
+all assertions in a given function, rendering the stack backtrace
+useless for identifying the specific failed assertion.
** It is a good idea to run Emacs under GDB (or some other suitable
debugger) *all the time*. Then, when Emacs crashes, you will be able
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