[RFC PATCH libinput] tools: run list-quirks from the git data when running from the builddir

[Peter Hutterer]

On Mon, Jun 25, 2018 at 11:06:36AM +0300, Pekka Paalanen wrote:
> On Fri, 22 Jun 2018 12:48:53 +1000
> Peter Hutterer <peter.hutterer at who-t.net> wrote:
> 
> > I'd like some comment on this from someone who knows this stuff better than
> > I do. The main goal is to have the same binary default to different search
> > paths, depending whether it's the installed version or the one run from the
> > build directory. This is the only solution I could come up with and it
> > works, but I'm not sure how much of that is coincidence vs "yes, this is how
> > ELF stripping works".
> > 
> > Any comments welcome. Or other solutions to this. Thanks
> > 
> > ---
> > 
> > Push the git data directory into a special variable in a custom ELF section.
> > Then after install, strip that ELF section out. The result is that when we're
> > running from the builddir, the data path is set and we read from there. When
> > running from the system install, the data path is zeroes only and we're
> > running with the defaults.
> 
> Hi Peter,
> 
> this is certainly interesting. I don't know about the correctness, but
> I have been wondering about how to disable the test suite scaffolding
> (e.g. WESTON_MODULE_MAP env var) in an installed weston instance.
> 
> I've also been thinking about how to expose private functions from a
> library for a test suite but prevent those from being accessed in an
> installed version. Maybe that could be an array of function pointers
> declared in a special section like you did, so it would disappear on
> install.

I guess the easiest approach here would be to link the library twice with
different symbol export tables (--version-script). This approach mostly
depends on whether you want to guarantee that you're running the same code
for testing and normal operation.

Or maybe there's some other approach where you can apply a symbol table to
an already-built library.

Cheers,
   Peter

> > 
> > Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
> > ---
> >  meson.build                     |  5 +++++
> >  tools/libinput-list-quirks.c    | 12 ++++++++++++
> >  tools/strip-builddir-section.sh | 18 ++++++++++++++++++
> >  3 files changed, 35 insertions(+)
> >  create mode 100644 tools/strip-builddir-section.sh
> > 
> > diff --git a/meson.build b/meson.build
> > index b650bbde..0b9dc751 100644
> > --- a/meson.build
> > +++ b/meson.build
> > @@ -479,6 +479,11 @@ libinput_list_quirks = executable('libinput-list-quirks',
> >  				  install_dir : libinput_tool_path,
> >  				  install : true
> >  				 )
> > +meson.add_install_script('tools/strip-builddir-section.sh',
> > +			 libinput_tool_path,
> > +			 'libinput-list-quirks')
> > +
> > +
> >  test('validate-quirks',
> >       libinput_list_quirks,
> >       args: ['--validate-only', '--data-dir=@0@'.format(join_paths(meson.source_root(), 'data'))]
> > diff --git a/tools/libinput-list-quirks.c b/tools/libinput-list-quirks.c
> > index 533c4f3a..1207ade3 100644
> > --- a/tools/libinput-list-quirks.c
> > +++ b/tools/libinput-list-quirks.c
> > @@ -207,6 +207,13 @@ usage(void)
> >  	       "	Validate the database\n");
> >  }
> >  
> > +/* When running from builddir, we use the git data tree by default.
> > +   This section is stripped on install.
> > + */
> > +static const char builddir_data_path[]
> > +	__attribute__ ((section ("builddir_section")))
> > +	= LIBINPUT_DATA_SRCDIR;
> > +
> >  int
> >  main(int argc, char **argv)
> >  {
> > @@ -219,6 +226,11 @@ main(int argc, char **argv)
> >  	struct quirks_context *quirks;
> >  	bool validate = false;
> >  
> > +	/* After the section is stripped, builddir_data_path is zeroes */
> > +	data_path = builddir_data_path;
> > +	if (data_path && strlen(data_path) == 0)
> > +		data_path = NULL;
> > +
> >  	while (1) {
> >  		int c;
> >  		int option_index = 0;
> > diff --git a/tools/strip-builddir-section.sh b/tools/strip-builddir-section.sh
> > new file mode 100644
> > index 00000000..dbae7964
> > --- /dev/null
> > +++ b/tools/strip-builddir-section.sh
> > @@ -0,0 +1,18 @@
> > +#!/bin/bash
> > +#
> > +# Usage: strip-builddir-section /path/to/libexec/libinput file1 file2
> > +
> > +directory=$1
> > +shift
> > +
> > +files="$@"
> > +
> > +pushd $directory > /dev/null
> > +for file in $files; do
> > +	if test -e $file; then
> > +		echo "Stripping file $directory/$file"
> > +		objcopy --remove-section builddir_section $file $file.tmp
> > +		mv $file.tmp $file
> > +	fi
> > +done
> > +popd > /dev/null
>