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From: Harald van Dijk
Subject: Two AX_PROG_CC_FOR_BUILD issues
Date: Sat, 13 Jul 2019 18:48:05 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.0


I am using AX_PROG_CC_FOR_BUILD to support cross-compilation. Some utilities are needed to generate files at build time, so these must not be built with a cross-compiler. This mostly works, except for two things.


When doing a native build, if CC is set and CC_FOR_BUILD is unset, I expect CC to be used for build-time jobs too. Instead, the default compiler is used. Would it be acceptable to change it to check whether a cross-compile is performed, and if not, if CC_FOR_BUILD is not set, just copy all the host compilation variables without doing any extra checks?


When CC and CC_FOR_BUILD are different, a few checks are done both for CC and for CC_FOR_BUILD, but they use the same cache variables. As a result, the CC results are also re-used for CC_FOR_BUILD. On an AIX system, configuring with ./configure CC=cc detected that the -qlanglvl=extc89 option was needed for C90 conformance, but it picked CC_FOR_BUILD=gcc and still used that same -qlanglvl=extc89 option. Needless to say, the build broke.

For 1, I have not yet looked at what would be needed to change this, since I do not know whether the current behaviour is by design.

For 2, I have looked a bit at what would be needed to change this, but it is problematic. For the flags, it is easy: just add a pushdef() and popdef() for ac_cv_prog_cc_c89, same as all the other variables. However, this is not the only check that is performed, and other checks are more difficult. There is AC_PROG_CC_C_O, but it is defined one way in Autoconf, and is redefined another way in Automake, using different cache variables. There is also _AC_LANG_COMPILER_GNU, where pushdef() and popdef() for the cache variable does not work, for reasons I have not yet figured out. Would it be okay to submit a patch just for the C90 conformance flag issue and to ignore the other problems?

Harald van Dijk

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