[libcamera-devel] [PATCH 02/11] libcamera: utils: Add a function to retrieve the libcamera source tree

[Laurent Pinchart]

Hi Kieran,

On Mon, Apr 27, 2020 at 11:11:35AM +0100, Kieran Bingham wrote:
> On 27/04/2020 04:17, Laurent Pinchart wrote:
> > Similarly to libcameraBuildPath(), there's a need to locate resources
> > within the source tree when running libcamera without installing it.
> > Support this use case with a new utils::libcameraSourcePath() function.
> 
> Eeeep.

I know :-S

> > The implementation currently leaks the path to the source tree in the
> > installed binary. The data is put in a separate section named .zero
> > which will need to be zeroed at installation time to fix this.
> 
> Indeed.
> 
> I guess we can't get any of this from the debug symbols can we? That
> won't be reliable.

Do we really want a debug symbols parser inside libcamera ? :-)

> > Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> 
> This is always going to be painful... but I don't think we should block
> this branch just because of leaking the source path - but we certainly
> want to fix it soon after.
> 
> Reviewed-by: Kieran Bingham <kieran.bingham at ideasonboard.com>

I'll try another approach, based on a symlink to the source tree inside
the build directory. If I can't do so in a reasonable amount of time
I'll merge this patch as-is and fix the issue on top.

> > ---
> >  meson.build                   |  2 ++
> >  src/libcamera/include/utils.h |  1 +
> >  src/libcamera/utils.cpp       | 37 ++++++++++++++++++++++++++++++++---
> >  3 files changed, 37 insertions(+), 3 deletions(-)
> > 
> > diff --git a/meson.build b/meson.build
> > index c6e6a934e54e..2058a6a77ceb 100644
> > --- a/meson.build
> > +++ b/meson.build
> > @@ -26,6 +26,8 @@ libcamera_version = libcamera_git_version.split('+')[0]
> >  cc = meson.get_compiler('c')
> >  config_h = configuration_data()
> >  
> > +config_h.set('LIBCAMERA_SOURCE_DIR', '"' + meson.current_source_dir() + '"')
> > +
> >  if cc.has_header_symbol('execinfo.h', 'backtrace')
> >      config_h.set('HAVE_BACKTRACE', 1)
> >  endif
> > diff --git a/src/libcamera/include/utils.h b/src/libcamera/include/utils.h
> > index 242eeded9d50..3334ff16613d 100644
> > --- a/src/libcamera/include/utils.h
> > +++ b/src/libcamera/include/utils.h
> > @@ -188,6 +188,7 @@ private:
> >  details::StringSplitter split(const std::string &str, const std::string &delim);
> >  
> >  std::string libcameraBuildPath();
> > +std::string libcameraSourcePath();
> >  
> >  } /* namespace utils */
> >  
> > diff --git a/src/libcamera/utils.cpp b/src/libcamera/utils.cpp
> > index 97f9b632e45b..056a67e93e0f 100644
> > --- a/src/libcamera/utils.cpp
> > +++ b/src/libcamera/utils.cpp
> > @@ -360,9 +360,10 @@ bool isLibcameraInstalled()
> >   *
> >   * During development, it is useful to run libcamera binaries directly from the
> >   * build directory without installing them. This function helps components that
> > - * need to locate resources, such as IPA modules or IPA proxy workers, by
> > - * providing them with the path to the root of the build directory. Callers can
> > - * then use it to complement or override searches in system-wide directories.
> > + * need to locate resources in the build tree, such as IPA modules or IPA proxy
> > + * workers, by providing them with the path to the root of the build directory.
> > + * Callers can then use it to complement or override searches in system-wide
> > + * directories.
> >   *
> >   * If libcamera has been installed, the build directory path is not available
> >   * and this function returns an empty string.
> > @@ -385,6 +386,36 @@ std::string libcameraBuildPath()
> >  	return dirname(info.dli_fname) + "/../../";
> >  }
> >  
> > +namespace {
> > +/* \todo Figure out a way to zero this section at install time */
> > +__attribute__((section(".zero")))
> > +const char sourceDirectory[] = LIBCAMERA_SOURCE_DIR;
> 
> Even if we can zero this out - it won't give us reproducible builds, as
> the section size will be dependant upon the size of the
> LIBCAMERA_SOURCE_DIR string.
> 
> Now I think about it - I can't recall if we hit the same issue on the
> buildPath too.
> 
> If this 'works for now' we can defer though.
> 
> > +} /* namespace */
> > +
> > +/**
> > + * \brief Retrieve the path to the source directory
> > + *
> > + * During development, it is useful to run libcamera binaries directly from the
> > + * build directory without installing them. This function helps components that
> > + * need to locate resources in the source tree, such as IPA configuration
> > + * files, by providing them with the path to the root of the source directory.
> > + * Callers can then use it to complement or override searches in system-wide
> > + * directories.
> > + *
> > + * If libcamera has been installed, the source directory path is not available
> > + * and this function returns an empty string.
> > + *
> > + * \return The path to the source directory if running from a build, or an empty
> > + * string otherwise
> > + */
> > +std::string libcameraSourcePath()
> > +{
> > +	if (isLibcameraInstalled())
> > +		return std::string();
> > +
> > +	return std::string(sourceDirectory) + "/";
> > +}
> > +
> >  } /* namespace utils */
> >  
> >  } /* namespace libcamera */

-- 
Regards,

Laurent Pinchart