[llvm-dev] Building an LLVM/CLANG cross compiler for legacy GCC toolchain

[Michael Dalpee via llvm-dev]

Hello,

I need to build a CLANG cross compiler for mips-linux-uclibc.  To be
completely compatible with the target system, I would like it to use linux
2.6.32.54 headers, binutils 2.25, gcc 4.1.2, and uClibc 0.9.30.1 for the
gcc toolchain.  I have been able to build the GCC toolchain a variety of
different ways, but none of these builds can be "dropped in" via clang as a
replacement for just using the gcc toolchain directly.  I am building the
toolchain on ubuntu 14.04 using gcc 4.8.4.

I believe this is because I do not understand how to build the toolchain
such that when clang invokes toolchain programs (particularly the linker),
those programs can find the things they need (include files, libraries,
etc) to operate properly.  This manifests itself in a variety of way
depending on what technique I used to build the toolchain, but here is a
representative problem from a toolchain I built using the buildroot system:

clang -v -target mips-linux-uclibc
--gcc-toolchain=/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr
--sysroot=/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr -o
build-mips-product/test-png  -fPIC
-I/home/mdalpee/checkouts/clang/source/src/program/include test_png.c png.c
../lib/build-mips-product/libutils.a

clang version 7.0.0 (trunk 328723)

Target: mips--linux-uclibc

Thread model: posix

InstalledDir: /home/milkweed/build-clang/bin

 "/home/mdalpee/build-clang/bin/clang-7.0" -cc1 -triple mips--linux-uclibc
-emit-obj -mrelax-all -disable-free -main-file-name png.c
-mrelocation-model pic -pic-level 2 -mthread-model posix -mdisable-fp-elim
-fmath-errno -masm-verbose -mconstructor-aliases -fuse-init-array
-target-cpu mips32r2 -target-feature -noabicalls -target-abi o32
-mfloat-abi hard -dwarf-column-info -debugger-tuning=gdb -v -resource-dir
/home/mdalpee/build-clang/lib/clang/7.0.0 -I
/home/mdalpee/checkouts/clang/source/src/program/include -isysroot
/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr
-internal-isystem
/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr/usr/local/include
-internal-isystem /home/mdalpee/build-clang/lib/clang/7.0.0/include
-internal-externc-isystem
/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr/include
-internal-externc-isystem
/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr/usr/include
-fdebug-compilation-dir
/home/mdalpee/checkouts/clang/source/src/program/png -ferror-limit 19
-fmessage-length 0 -fobjc-runtime=gcc -fdiagnostics-show-option -o
/tmp/png-b34eab.o -x c png.c

clang -cc1 version 7.0.0 based upon LLVM 7.0.0svn default target
x86_64-unknown-linux-gnu

ignoring nonexistent directory
"/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr/usr/local/include"

ignoring nonexistent directory
"/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr/usr/include"

#include "..." search starts here:

#include <...> search starts here:

 /home/mdalpee/checkouts/clang/source/src/program/include

 /home/mdalpee/build-clang/lib/clang/7.0.0/include

 /home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr/include

End of search list.

 "/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr/bin/mips-linux-uclibc-ld"
--sysroot=/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr -z
relro --sysroot=/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr
--eh-frame-hdr -m elf32btsmip -dynamic-linker /lib/ld.so.1 -o
build-mips-product/test-png
/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr/lib/../lib/crt1.o
/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr/lib/../lib/crti.o
crtbegin.o
-L/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr/lib/../lib
-L/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr/lib
/tmp/test_png-2da555.o /tmp/png-b34eab.o
../lib/build-mips-product/libutils.a -lgcc --as-needed -lgcc_s
--no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed crtend.o
/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr/lib/../lib/crtn.o

/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr/bin/mips-linux-uclibc-ld:
cannot find crtbegin.o: No such file or directory

/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr/bin/mips-linux-uclibc-ld:
cannot find -lgcc

/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr/bin/mips-linux-uclibc-ld:
cannot find -lgcc_s

/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr/bin/mips-linux-uclibc-ld:
cannot find /lib/libc.so.0 inside
/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr

/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr/bin/mips-linux-uclibc-ld:
cannot find /usr/lib/uclibc_nonshared.a inside
/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr

/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr/bin/mips-linux-uclibc-ld:
cannot find /lib/ld-uClibc.so.0 inside
/home/mdalpee/buildroot-2009.05/build_mips/staging_dir/usr

clang-7.0: error: linker command failed with exit code 1 (use -v to see
invocation)

make[4]: *** [build-mips-product/test-png] Error 1

make[3]: *** [png] Error 2


Any guidance about how to best create the gcc toolchain (particularly how
to properly build gcc to use uclibc instead of glibc) would be appreciated.
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