cleanup a tad
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Copyright 2001 Red Hat Inc., Egor Duda
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Copyright 2001, 2002 Red Hat Inc., Egor Duda
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So, your favorite program has crashed? And did you say something about
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'stackdump'? Or it just prints its output from left to right and
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@ -9,14 +9,17 @@ you can do something better than that. You can debug the problem
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yourself, and even if you can't fix it, your analysis may be very
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helpful. Here's the (incomplete) howto on cygwin debugging.
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1. The first thing you'll need to do is to build cygwin1.dll and your
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1. First things first
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The first thing you'll need to do is to build cygwin1.dll and your
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crashed application from sources. To debug them you'll need debug
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information, which is normally stripped from executables. You probably
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also want to build a version of the dll with more debugging capabilities
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by reconfiguring your build directory, specifying the --enable-debugging
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option to configure.
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2. Create known-working cygwin debugging environment.
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2. Creating a known-working cygwin debugging environment
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- create a separate directory, say, c:\cygdeb, and put known-working
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cygwin1.dll and gdb.exe in it.
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- create a wrapper c:\cygdeb\debug_wrapper.cmd:
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@ -28,13 +31,15 @@ set CYGWIN_TESTING=1
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c:\cygdeb\gdb.exe -nw %1 %2
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===================================
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3. Try to use cygwin's JIT debugging facility:
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3. Using cygwin's JIT debugging facility
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add 'error_start=c:\cygdeb\debug_wrapper.cmd' to CYGWIN environment
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variable. When some application encounters critical error, cygwin will stop
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it and execute debug_wrapper.cmd, which will run gdb and make it to attach to
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the crashed application.
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4. Strace.
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4. Strace
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You can run your program under 'strace' utility, described if user's manual.
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If you know where the problem approximately is, you can add a bunch of
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additional debug_printf()s in the source code and see what they print in
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@ -49,7 +54,8 @@ c:\cygdeb\gdb.exe -nw %1 %2
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starts does not inherit a cygwin environment. It is equivalent to starting
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a program from the command prompt.
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5. Problems at early startup.
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5. Problems at early startup
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Sometimes, something crashes at the very early stages of application
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initialization, when JIT debugging facility is not yet active. Ok, there's
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another environment variable that may help. Create program_wrapper.cmd:
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@ -71,6 +77,8 @@ c:\some\path\bad_program.exe some parameters
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After that you can normally step through the code in cygwin1.dll and
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bad_program.exe
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6. More problems at early startup
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You can also set a CYGWIN_DEBUG variable to force the debugger to pop up
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only when a certain program is run:
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@ -84,7 +92,8 @@ set CYGWIN_DEBUG=cat.exe=gdb.exe
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Note that it bears repeating that both of the above options are *only*
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available when configuring cygwin with --enable-debugging.
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6. Heap corruption.
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7. Heap corruption
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If your program crashes at malloc() or free() or when it references some
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malloc()'ed memory, it looks like heap corruption. You can configure and
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build special version of cygwin1.dll which includes heap sanity checking.
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@ -92,7 +101,8 @@ set CYGWIN_DEBUG=cat.exe=gdb.exe
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however, that this version of dll is _very_ slow (10-100 times slower than
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normal), so use it only when absolutely necessary.
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7. Program dies when running under strace.
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8. Program dies when running under strace
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If your program crashes when you run it using strace but runs ok (or has a
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different problem) otherwise, then there may be a problem in one of the
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strace *_printf statements. Usually this is caused by a change in arguments
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