Re: [Libguestfs] [nbdkit PATCH] cc: Allow configuration without absolute paths

On Fri, Aug 18, 2023 at 08:27:45AM -0500, Eric Blake wrote: > In https://gitlab.com/nbdkit/nbdkit/-/merge_requests/30, Khem reports > that in a cross-compilation environment, nbdkit embeds the absolute > name of the cross-compiler into the resulting cc plugin, even though > running the plugin should be favoring the bare name 'cc'. This in > turn leads to non-reproducible builds. As the goal of cross-compiling > nbdkit is to produce a binary that behaves identically regardless of > the build environment used, this means we need to give the user > control over the defaults for CC and CFLAGS embedded into the cc > plugin. > > However, instead of trying to munge the build environment variable as > suggested in that merge request, I found it cleaner to just add > additional precious variables to be set at configure time, as in: > > ./configure CC=/path/to/cross-compiler CC_PLUGIN_CC='ccache gcc' ... > > Reported-by: Khem Raj > Signed-off-by: Eric Blake <eblake(a)redhat.com&gt;

> --- > > gitlab doesn't let me see the right email address to cc; if I can > figure that out, I'll tweak the Reported-by line as appropriate before > committing... > --- > plugins/cc/nbdkit-cc-plugin.pod | 9 ++++++--- > configure.ac | 11 +++++++++++ > plugins/cc/Makefile.am | 4 ++-- > 3 files changed, 19 insertions(+), 5 deletions(-) > > diff --git a/plugins/cc/nbdkit-cc-plugin.pod b/plugins/cc/nbdkit-cc-plugin.pod > index 2974890c..2bc3cfb8 100644 > --- a/plugins/cc/nbdkit-cc-plugin.pod > +++ b/plugins/cc/nbdkit-cc-plugin.pod > @@ -45,9 +45,12 @@ To replace the compiler flags: > > The plugin parameters C<CC>, C<CFLAGS> and C<EXTRA_CFLAGS> (written in > uppercase) can be used to control which C compiler and C compiler > -flags are used. If not set, the default compiler and flags from when > -nbdkit was itself compiled from source are used. To see what those > -were you can do: > +flags are used. If not set, you can hardcode the defaults for C<CC> > +and C<CFLAGS> at the time nbdkit is compiled from source by > +configuring with C<CC_PLUGIN_CC=...> and C<CC_PLUGIN_CFLAGS=...>, > +otherwise, the configuration for compiling nbdkit itself is used > +(C<EXTRA_CFLAGS> can only be set from the command line when starting > +the cc plugin). To see what those were you can do: > > $ nbdkit cc --dump-plugin > ... Widening the context, ... CC=gcc CFLAGS=-g -O2 -fPIC -shared The C<CFLAGS> parameter overrides the built-in flags completely. The C<EXTRA_CFLAGS> parameter adds extra flags to the built-in flags. Since we already mention EXTRA_CFLAGS below the example, I'm not sure if my addition of a parenthetical about EXTRA_CFLAGS above is worthwhile, or just adds noise.

> diff --git a/configure.ac b/configure.ac > index afc5ddab..e5e261c8 100644 > --- a/configure.ac > +++ b/configure.ac > @@ -820,6 +820,15 @@ AC_ARG_ENABLE([plugins], > [disable all bundled plugins and filters])]) > AM_CONDITIONAL([HAVE_PLUGINS], [test "x$enable_plugins" != "xno"]) > > +dnl For the cc plugin, let the user hard-code their preferred compiler setup > +dnl Default to the settings used for nbdkit itself > +AC_ARG_VAR([CC_PLUGIN_CC], > + [Value to use for CC when building the cc plugin, default $CC]) I'm wondering if there is a better way to word this (it shows up in './configure --help' output). Maybe: [Value to hard-code into the cc plugin's default for CC, instead of $CC]

> +: "${CC_PLUGIN_CC:=$CC}" > +AC_ARG_VAR([CC_PLUGIN_CFLAGS], > + [Value to use for CFLAGS when building the cc plugin, default $CFLAGS]) > +: "${CC_PLUGIN_CFLAGS:=$CFLAGS}" and similar