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Re: missing backslash escaping in AC_TRY_EVAL yields binary data in conf

From: Nick Bowler
Subject: Re: missing backslash escaping in AC_TRY_EVAL yields binary data in config.log with dash
Date: Tue, 2 Oct 2018 09:31:33 -0400

On 10/2/18, Vincent Lefevre <address@hidden> wrote:
> I originally reported this bug in libtool:
>   https://debbugs.gnu.org/cgi/bugreport.cgi?bug=21309
> but this actually seems to be a bug in AC_TRY_EVAL (or another macro
> it uses).

AC_TRY_EVAL is not documented in the Autoconf manual.

Drilling into the Autoconf source, we find that this is intentional:

  # The AC_TRY_EVAL and AC_TRY_COMMAND macros are dangerous and
  # undocumented, and should not be used.
  # They may be removed or their API changed in a future release.
  # Autoconf itself no longer uses these two macros; they are present
  # only for backward compatibility with previous versions of Autoconf.
  # Not every shell command will work due to problems with eval
  # and quoting, and the rules for exactly what does work are tricky.
  # Worse, due to double-expansion during evaluation, arbitrary unintended
  # shell commands could be executed in some situations.

If libtool is still using this macro, and it is causing problems,
then this does seem like a bug in libtool.  The solution would seem
to be for libtool to stop using AC_TRY_EVAL.


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