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

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 ...

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])

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