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 <bonz...@gnu.org> --- lib/autoconf/general.m4 | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) 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], [AS_ECHO(["AS_ESCAPE([$1], [""])"]) >>confdefs.h], [cat >>confdefs.h <<_ACEOF [$1] -- 2.7.4