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Corinna Vinschen 30add3e6b3 Cygwin: exec: don't access cygheap before it's initialized
This is a long-standing thinko.

When you exec a process, dll_crt0_0 in the child process calls
child_info_spawn::handle_spawn().  handle_spawn() initialises the
cygheap.

Now consider calling strace.  Strace is a non-Cygwin process dynamically
loading cygwin1.dll via LoadLibrary.  This in turn initializes the DLL:

- dll_crt0_0 finds that the process it attaches to has been exec'd, so
  child_info_spawn::handle_spawn() is called.

- If the DLL is being dynamically loaded, handle_spawn() calls
  child_info_spawn::get_parent_handle().  This in turn tries to set
  the moreinfo->myself_pinfo value inside the cygheap to NULL.

- However, at this time, the cygheap has not yet been initialized.  This
  only occurs in the cygheap_fixup_in_child() call after get_parent_handle()
  returns.

--> SEGV

This thinko never had a negative side effect, because the cygheap was
pre-allocated at DLL load time until commit 2f9b8ff00c ("Cygwin:
decouple cygheap from Cygwin DLL").  With 2f9b8ff00c, the cygheap
actually doesn't exist until after the call to cygheap_fixup_in_child().

Fix this problem by moving the assignment after the call to
cygheap_fixup_in_child().

Fixes: 3de7be4c1d ("* DevNotes: Add entry cgf-000007. [...]")
Fixes: 2f9b8ff00c ("Cygwin: decouple cygheap from Cygwin DLL")
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>
2022-12-01 22:34:53 +01:00
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README

		   README for GNU development tools

This directory contains various GNU compilers, assemblers, linkers, 
debuggers, etc., plus their support routines, definitions, and documentation.

If you are receiving this as part of a GDB release, see the file gdb/README.
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see libg++/README, etc.  That'll give you info about this
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It is now possible to automatically configure and build a variety of
tools with one command.  To build all of the tools contained herein,
run the ``configure'' script here, e.g.:

	./configure 
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then do:
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(If the configure script can't determine your type of computer, give it
the name as an argument, for instance ``./configure sun4''.  You can
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If you have more than one compiler on your system, it is often best to
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	CC=gcc ./configure
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A similar example using csh:

	setenv CC gcc
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