[libcamera-devel] [PATCH v4 5/6] libcamera: ipa_manager: Search for IPA libraries in build tree

[Kieran Bingham]

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 ...

v4:
 - rebase and cleanup
---
 src/libcamera/ipa_manager.cpp | 52 ++++++++++++++++++++++++++++++++++-
 src/libcamera/meson.build     |  6 ++++
 2 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/src/libcamera/ipa_manager.cpp b/src/libcamera/ipa_manager.cpp
index de99a0bc3ce1..a5f2707f6788 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 +27,35 @@
  * \brief Image Processing Algorithm module manager
  */
 
+static bool isLibcameraInstalled()
+{
+	/* musl doesn't declare _DYNAMIC in link.h, declare it manually. */
+	extern ElfW(Dyn) _DYNAMIC[];
+
+	/*
+	 * DT_RUNPATH (DT_RPATH when the linker uses old dtags) is removed on
+	 * install.
+	 */
+	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;
+	}
+
+	return true;
+}
+
+static const char *libcameraPath()
+{
+	Dl_info info;
+
+	/* Look up our own symbol. */
+	int ret = dladdr(reinterpret_cast<void *>(libcameraPath), &info);
+	if (ret == 0)
+		return nullptr;
+
+	return info.dli_fname;
+}
+
 namespace libcamera {
 
 LOG_DEFINE_CATEGORY(IPAManager)
@@ -112,7 +144,25 @@ 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. We need to recurse 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. */
 	ipaCount += addDir(IPA_MODULE_DIR);
 
 	if (!ipaCount)
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.
+
 libcamera = shared_library('camera',
                            libcamera_sources,
                            install : true,
                            link_with : libcamera_link_with,
                            include_directories : includes,
+                           build_rpath : '/',
                            dependencies : libcamera_deps)
 
 libcamera_dep = declare_dependency(sources : [libcamera_api, libcamera_ipa_api, libcamera_h],
-- 
2.20.1