[libcamera-devel] [PATCH v3 5/6] libcamera: ipa_manager: Search for IPA libraries in build tree

[Laurent Pinchart]

Hi Kieran,

Thank you for the patch.

On Thu, Feb 20, 2020 at 04:57:03PM +0000, Kieran Bingham wrote:
> When libcamera is built and tested (or used at all) before installing to
> the configured prefix path, it will be unable to locate the IPA
> binaries, or IPA binaries previously installed in the system paths may
> be incorrect to load.
> 
> Utilise the build_rpath dynamic tag which is stripped out by meson at
> install time to determine at runtime if the library currently executing
> has been installed or not.
> 
> When not installed and running from a build tree, identify the location
> of that tree by finding the path of the active libcamera.so itself, and
> from that point add a relative path to be able to load the most recently
> built IPA modules.
> 
> Signed-off-by: Kieran Bingham <kieran.bingham at ideasonboard.com>
> 
> ---
> v2:
>  - Move get_runpath to ipa_manager.c : libcamera::elfRunPath()
>  - Minor fixes
>  - Squash elfRunPath() into this patch
> 
> v3:
>  - Full rework. It's just all different :-)
>  - Maybe this one is going to cut it ...
> ---
>  src/libcamera/ipa_manager.cpp | 46 ++++++++++++++++++++++++++++++++++-
>  src/libcamera/meson.build     |  6 +++++
>  2 files changed, 51 insertions(+), 1 deletion(-)
> 
> diff --git a/src/libcamera/ipa_manager.cpp b/src/libcamera/ipa_manager.cpp
> index 3b1d4c0b295e..e60bf3dabebe 100644
> --- a/src/libcamera/ipa_manager.cpp
> +++ b/src/libcamera/ipa_manager.cpp
> @@ -9,6 +9,9 @@
>  
>  #include <algorithm>
>  #include <dirent.h>
> +#include <dlfcn.h>
> +#include <elf.h>
> +#include <link.h>
>  #include <string.h>
>  #include <sys/types.h>
>  
> @@ -24,6 +27,30 @@
>   * \brief Image Processing Algorithm module manager
>   */
>  
> +static bool isLibcameraInstalled()
> +{

I'd add a comment here to state

	/* musl doesn't declare _DYNAMIC in link.h, declare it manually. */

to remember this is here for a reason.

> +	extern ElfW(Dyn) _DYNAMIC[];

Maybe add a blank line here ?

> +	/* DT_RUNPATH (DT_RPATH on musl) is removed on install. */

Do we really need to check for DT_RPATH ? As far as I know the tag that
is generated depends solely on the linker version, not on the C library.
Does musl really generate DT_RPATH ?

> +	for (const ElfW(Dyn) *dyn = _DYNAMIC; dyn->d_tag != DT_NULL; ++dyn)
> +		if (dyn->d_tag == DT_RUNPATH || dyn->d_tag == DT_RPATH)
> +			return false;

Braces for the 'for' ?

> +
> +	return true;
> +}
> +
> +static const char *libcameraPath()
> +{
> +	Dl_info info;
> +	int ret;
> +
> +	/* look up our own symbol. */

s/look/Look/

That's a neat way to do it, we could have used an unrelated static
function (such as IPAManager::instance) and inlined this code in
IPAManager::IPAManager, but create a separate static function makes the
code self-contained.

> +	ret = dladdr(reinterpret_cast<void *>(libcameraPath), &info);
> +	if (ret == 0)
> +		return nullptr;
> +
> +	return info.dli_fname;
> +}

I would move these two functions just above IPAManager::IPAManager to
keep them close to the location where they're used.

> +
>  namespace libcamera {
>  
>  LOG_DEFINE_CATEGORY(IPAManager)
> @@ -108,7 +135,24 @@ IPAManager::IPAManager()
>  				<< "No IPA found in '" << modulePaths << "'";
>  	}
>  
> -	/* Load IPAs from the installed system path. */
> +	/*
> +	 * When libcamera is used before it is installed, load IPAs from the
> +	 * same build directory as the libcamera library itself. This requires
> +	 * identifying the path of the libcamera.so, and referencing a relative
> +	 * path for the IPA from that point.

Maybe add "We need to recursive into one level of sub-directories to
match the build tree." ?

> +	 */
> +	if (!isLibcameraInstalled()) {
> +		std::string ipaBuildPath = utils::dirname(libcameraPath()) + "/../ipa";
> +		constexpr int maxDepth = 1;
> +
> +		LOG(IPAManager, Info)
> +			<< "libcamera is not installed. Adding '"
> +			<< ipaBuildPath << "' to the IPA search path";
> +
> +		ipaCount += addDir(ipaBuildPath.c_str(), maxDepth);
> +	}
> +
> +	/* Finally try to load IPAs from the installed system path. */
>  	ret = addDir(IPA_MODULE_DIR);
>  	if (ret > 0)
>  		ipaCount += ret;
> diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build
> index 1e5b54b34078..88658ac563f7 100644
> --- a/src/libcamera/meson.build
> +++ b/src/libcamera/meson.build
> @@ -107,11 +107,17 @@ if get_option('android')
>      libcamera_link_with += android_camera_metadata
>  endif
>  
> +# We add '/' to the build_rpath as a 'safe' path to act as a boolean flag.
> +# The build_rpath is stripped at install time by meson, so we determine at
> +# runtime if the library is running from an installed location by checking
> +# for the presence or abscence of the dynamic tag.

s/abscence/absence/

Don't tell me this is a UK spelling :-)

> +
>  libcamera = shared_library('camera',
>                             libcamera_sources,
>                             install : true,
>                             link_with : libcamera_link_with,
>                             include_directories : includes,
> +                           build_rpath : '/',
>                             dependencies : libcamera_deps)

I double-checked based on what criteria build_rpath would generate
DT_RPATH or DT_RUNPATH. It turns out this is controlled by the
--enable-new-dtags and --disable-new-dtags options to ld, with the
format generating DT_RUNPATH and the latter DT_RPATH. None of these
are set by meson by default. GNU ld defaulted to --enable-new-dtags in
binutils v2.24, released on December 2013, before gcc 5.1 (April 2015)
which is the earliest compiler version we support (I'm actually not even
sure we support gcc 5.1, I have gcc 5.4 installed in my test setup,
released on June 2016). Debian Jessie ships binutils v2.25 and Ubuntu
16.04 ships binutils v2.26. We should thus be safe.

Assuming the DT_RPATH comment for musl isn't right and the corresponding
condition can be removed,

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

Otherwise let's discuss it.

>  
>  libcamera_dep = declare_dependency(sources : [libcamera_api, libcamera_ipa_api, libcamera_h],

-- 
Regards,

Laurent Pinchart