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To build libfuzzer package Matthew Weber noticed that (host) clang
doesn't run on the host without "-B $(HOST_DIR)/opt/ext-toolchain"
option. This option add a new search path for binaries and object
files used implicitly.
Without -B clang fail to link due to missing crtbeging.o file and libgcc:
output/host/bin/aarch64-linux-gnu-ld: cannot find crtbegin.o: No such file or directory
output/host/bin/aarch64-linux-gnu-ld: cannot find -lgcc
Indeed, clang search path doesn't include the dafault cross-gcc's search paths:
$ output/host/bin/clang -print-search-dirs
programs: = output/host/bin:output/host/bin:/..//bin
libraries: = output/host/lib/clang/8.0.0:
output/host/bin/../lib64:
/lib/../lib64:
/usr/lib/../lib64:
output/host/bin/../lib:
/lib:/usr/lib
Here is the same command for cross-gcc:
$ output/host/bin/aarch64-linux-gnu-gcc -print-search-dirs
install: output/host/opt/ext-toolchain/bin/../lib/gcc/aarch64-linux-gnu/8.3.0/
programs: = output/host/opt/ext-toolchain/bin/../libexec/gcc/aarch64-linux-gnu/8.3.0/:
output/host/opt/ext-toolchain/bin/../libexec/gcc/:
output/host/opt/ext-toolchain/bin/../lib/gcc/aarch64-linux-gnu/8.3.0/../../../../aarch64-linux-gnu/bin/aarch64-linux-gnu/8.3.0/:
output/host/opt/ext-toolchain/bin/../lib/gcc/aarch64-linux-gnu/8.3.0/../../../../aarch64-linux-gnu/bin/
libraries: = output/opt/ext-toolchain/bin/../lib/gcc/aarch64-linux-gnu/8.3.0/:
output/host/opt/ext-toolchain/bin/../lib/gcc/:
output/host/opt/ext-toolchain/bin/../lib/gcc/aarch64-linux-gnu/8.3.0/../../../../aarch64-linux-gnu/lib/aarch64-linux-gnu/8.3.0/:
output/host/opt/ext-toolchain/bin/../lib/gcc/aarch64-linux-gnu/8.3.0/../../../../aarch64-linux-gnu/lib/../lib64/:
output/host/aarch64-buildroot-linux-gnu/sysroot/lib/aarch64-linux-gnu/8.3.0/:
output/host/aarch64-buildroot-linux-gnu/sysroot/lib/../lib64/:
output/host/aarch64-buildroot-linux-gnu/sysroot/usr/lib/aarch64-linux-gnu/8.3.0/:
output/host/aarch64-buildroot-linux-gnu/sysroot/usr/lib/../lib64/:
output/host/opt/ext-toolchain/bin/../lib/gcc/aarch64-linux-gnu/8.3.0/../../../../aarch64-linux-gnu/lib/:
output/host/aarch64-buildroot-linux-gnu/sysroot/lib/:
output/host/aarch64-buildroot-linux-gnu/sysroot/usr/lib/
We can see that gcc default search path contains
"output/host/opt/ext-toolchain" directory where the external toolchain
has been extracted.
Since we want to use clang without additional option like -B,
patch clang in order to use GCC_INSTALL_PREFIX instead of
using automatic detection (which doesn't work for Buildroot).
We eventually want to relocate the Buildroot SDK containing the clang
cross-compiler, so we provide a relative path to GCC_INSTALL_PREFIX
in order to avoid to hardcode the path to the GCC toolchain.
Also the path between clang and the GCC external toolchain is not always
the same, we have the following case:
* Toolchain to be downloaded and installed
The toolchain is extracted into $(HOST_DIR)/opt/ext-toolchain, so the
path is "../opt/ext-toolchain".
* Pre-installed toolchain
The toolchain is localed somewhere in the host filesystem and
defined by the user using BR2_TOOLCHAIN_EXTERNAL_PATH.
So, set GCC_INSTALL_PREFIX using realpath:
-DGCC_INSTALL_PREFIX:PATH=`realpath --relative-to=$(HOST_DIR)/bin/ $(TOOLCHAIN_EXTERNAL_INSTALL_DIR)`
When we use a Buildroot's internal toolchain, clang will find theses
crt*.o files and libgcc.
http://lists.busybox.net/pipermail/buildroot/2019-August/256204.html
Signed-off-by: Romain Naour <romain.naour@smile.fr>
Cc: Matthew Weber <matthew.weber@rockwellcollins.com>
Cc: Valentin Korenblit <valentinkorenblit@gmail.com>
Tested-by: Matt Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Buildroot is a simple, efficient and easy-to-use tool to generate embedded Linux systems through cross-compilation. The documentation can be found in docs/manual. You can generate a text document with 'make manual-text' and read output/docs/manual/manual.text. Online documentation can be found at http://buildroot.org/docs.html To build and use the buildroot stuff, do the following: 1) run 'make menuconfig' 2) select the target architecture and the packages you wish to compile 3) run 'make' 4) wait while it compiles 5) find the kernel, bootloader, root filesystem, etc. in output/images You do not need to be root to build or run buildroot. Have fun! Buildroot comes with a basic configuration for a number of boards. Run 'make list-defconfigs' to view the list of provided configurations. Please feed suggestions, bug reports, insults, and bribes back to the buildroot mailing list: buildroot@buildroot.org You can also find us on #buildroot on OFTC IRC. If you would like to contribute patches, please read https://buildroot.org/manual.html#submitting-patches