Hello,
the Autoconf manual states for “Macro: AC_PROG_CC ([compiler-search-list])”:
“If using the GNU C compiler, set shell variable GCC to ‘yes’. If output variable CFLAGS was not already set, set it to
-g -O2 for the GNU C compiler (-O2 on systems where GCC does not accept -g), or -g for other compilers. If your package
does not like this default, then it is acceptable to insert the line “: ${CFLAGS=""}” after AC_INIT and before
AC_PROG_CC to select an empty default instead.”
The common pattern is, that
• when CONFIG_SITE rules do not apply, calling “./configure” implies passing -g -O2 to the compiler
• when CONFIG_SITE rules do not apply, calling “CFLAGS=-flto” implies passing -flto but no -g -O2 to the compiler
• when CONFIG_SITE rules do apply, calling “./configure” implies CFLAGS specified in config.site
With “: ${CFLAGS=""}” the third bullet/expectation still applies, but not the first two.
So when one wants debug information in all self-compiled autoconf-based packages, the user has to put CFLAGS=-g -O2 in
CONFIG_SITE. Then it does not matter, if the package maintainer likes the default, the package is compiled with the
“default -g -O2”.
But if the user just calls ./configure without CONFIG_SITE, then the package maintainer is per documentation allowed to
tweak the default CFLAGS.
What is the rationale for this?
Usually I have CFLAGS=-O3 -flto in CONFIG_SITE and when I want to have debug information, I remove the overwriting from
CONFIG_SITE. Reading the documentation this does not seem to be the right way to have debug information in a package, I
am supposed to add -g in CFLAGS in CONFIG_SITE.
Quite cumbersome… Posgresql goes beyond this by having “unset CFLAGS” in configure.in. This is not much different than
: ${CFLAGS=""}, except it completely ignores CONFIG_SITE. When compiling Postgresql CONFIG_SITE-users are supposed to
hack the resulting files and tweak them for LTO…
The documentation of Autoconf is supposed recommend common behavior of Autoconf-based packages, on which users can rely.
Regards
Дилян
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