Re: [PATCH 3/3] autoconf: refine quadrigraph test in _AC_DEFINE_UNQUOTED
Eric Blake <[email protected]>
| Newsgroups | gmane.comp.sysutils.autoconf.patches |
|---|---|
| Organization | Red Hat, Inc. |
| Message-ID | <[email protected]> |
On 10/31/2016 06:39 AM, Paolo Bonzini wrote:
> It is a very common case that a quadrigraph appears in the argument of
> _AC_DEFINE_UNQUOTED, because "#define" is expanded through a quadrigraph.
> Therefore, restrict the quadrigraph tests to "$" (for "$(" and "${")
> and "(" (for "$(").
>
> At the same time, "#" should not be used inside AC_ECHO because it confuses
> m4's comment parsing. This pre-existing latent bug is caught by test 251:
>
> AC_DEFINE_UNQUOTED([bar], [[%!_!# X]])
>
> Previously the quadrigraph in "@%:@define bar %!_!# X" made Autoconf fall back
> to cat anyway. Now that Autoconf is not fooled by the quadrigraph, the test
> catches that "#" is not special-cased. Kudos to Eric for coming up with it!
>
> * lib/autoconf/general (_AC_DEFINE_UNQUOTED): Do not blindly
> use cat on all quadrigraphs.
>
> Signed-off-by: Paolo Bonzini <[email protected]>
> ---
> lib/autoconf/general.m4 | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
ACK.
>
> diff --git a/lib/autoconf/general.m4 b/lib/autoconf/general.m4
> index c15fb13..ef6285d 100644
> --- a/lib/autoconf/general.m4
> +++ b/lib/autoconf/general.m4
> @@ -2167,9 +2167,11 @@ m4_define([AC_DEFINE_UNQUOTED], [_AC_DEFINE_Q([_$0], $@)])
> # Append the pre-expanded STRING and a newline to confdefs.h, as if
> # with an unquoted here-doc, but avoiding a fork in the common case of
> # no backslash, no command substitution, no complex variable
> -# substitution, and no quadrigraphs.
> +# substitution (taking into account quadrigraphs as well). Also
> +# avoid AS_ECHO if "#" is present to avoid confusing m4 with comments,
> +# but quadrigraphs are fine in that case.
> m4_define([_AC_DEFINE_UNQUOTED],
> -[m4_if(m4_bregexp([$1], [\\\|`\|\$(\|\${\|@]), [-1],
> +[m4_if(m4_bregexp([$1], [#\|\\\|`\|\(\$\|@S|@\)\((|{|@{:@\)]), [-1],
Line noise for the win!
> [AS_ECHO(["AS_ESCAPE([$1], [""])"]) >>confdefs.h],
> [cat >>confdefs.h <<_ACEOF
> [$1]
>
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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