{"slug":"cross-gcc","title":"cross-gcc","summary":"Use when compiling for ARM, AArch64, RISC-V, or MIPS from x86-64 with a GCC cross toolchain: triplets, sysroots, pkg-config, CMake toolchain files, QEMU. Not for Zig: use zig-cross.","platform":"Claude","tags":[],"authorName":"LLM Mart","authorSlug":"llm-mart","score":0,"source":"github","price":null,"verified":false,"createdAt":"2026-09-30T19:50:11.620244Z","repo":{"url":"https://github.com/OutlineDriven/outline-driven-development","stars":54,"forks":10,"license":"Apache-2.0","updatedAt":"2026-09-28T03:16:21Z"},"bodyHtml":"
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name: cross-gcc\ndescription: 'Use when compiling for ARM, AArch64, RISC-V, or MIPS from x86-64 with a GCC cross toolchain: triplets, sysroots, pkg-config, CMake toolchain files, QEMU. Not for Zig: use zig-cross.'

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Cross-compilation with GCC

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Contract

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FieldBound contract
TriggerThe user needs to build for a different architecture with a <triplet>-gcc toolchain, gets Exec format error or wrong ELF class, finds host libraries leaking into a cross link, or wants to run and debug a cross-built binary under QEMU.
AuthorityRead-only. The skill emits install commands, compiler invocations, environment settings, and a toolchain file to chat; the user runs them. Rollback is not needed. No remote mutation.
Side effectChat output. Confirmation compiles run on scratch files.
DoneThe triplet, toolchain, sysroot, and build-system wiring are stated for the target, every flag is confirmed against the GCC target-options documentation or the installed cross compiler, and each error in the request has a cause and fix.
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Inputs

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Procedure

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  1. Choose the triplet <arch>-<vendor>-<os>-<abi>, three or four parts. Common values: aarch64-linux-gnu (64-bit ARM, glibc), arm-linux-gnueabihf (32-bit ARM, hard float), arm-none-eabi (bare-metal ARM), riscv64-linux-gnu, mipsel-linux-gnu, x86_64-w64-mingw32 (Windows from Linux). Done when: one triplet is chosen.

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    2. \n

  2. Install and confirm the toolchain. Debian and Ubuntu: apt install gcc-aarch64-linux-gnu g++-aarch64-linux-gnu binutils-aarch64-linux-gnu; bare-metal ARM: apt install gcc-arm-none-eabi. Confirm with aarch64-linux-gnu-gcc --version. Done when: the compiler prints its version.

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    3. \n

  3. Compile. Hosted: aarch64-linux-gnu-gcc -O2 -o hello hello.c, aarch64-linux-gnu-g++ -O2 -std=c++20 -o hello hello.cpp. Bare-metal Cortex-M4: arm-none-eabi-gcc -mcpu=cortex-m4 -mthumb -mfloat-abi=hard -mfpu=fpv4-sp-d16 -ffreestanding -nostdlib -nostartfiles -T linker.ld -o firmware.elf startup.s main.c. Target flags from the reference: -march, -mcpu, -mthumb, -mfloat-abi=soft|softfp|hard, -mfpu, and for AArch64 -moutline-atomics; RISC-V uses -march=rv64gc -mabi=lp64d style ISA strings. Done when: the compile command names the CPU and ABI.

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  4. Add a sysroot when the program links target libraries: --sysroot=/path/to/sysroot on every compile and link. Sources: a vendor image, debootstrap --arch arm64 <suite> <dir> for Debian, or the Yocto or Buildroot output tree. Confirm with aarch64-linux-gnu-gcc --sysroot=<dir> -v -E - < /dev/null 2>&1 | grep sysroot. Done when: the sysroot path appears in the compiler's verbose output.

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  5. Redirect pkg-config, which returns host paths by default: export PKG_CONFIG_SYSROOT_DIR=<sysroot>, export PKG_CONFIG_LIBDIR=$PKG_CONFIG_SYSROOT_DIR/usr/lib/aarch64-linux-gnu/pkgconfig:$PKG_CONFIG_SYSROOT_DIR/usr/share/pkgconfig, export PKG_CONFIG_PATH=. Check with pkg-config --libs <lib>. Done when: the printed paths are under the sysroot.

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  6. Wire the build system. Environment for Make and autoconf: CC, CXX, AR, STRIP, OBJDUMP set to the triplet-prefixed tools, and ./configure --host=aarch64-linux-gnu. CMake toolchain file:

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    set(CMAKE_SYSTEM_NAME Linux)\nset(CMAKE_SYSTEM_PROCESSOR aarch64)\nset(CMAKE_C_COMPILER aarch64-linux-gnu-gcc)\nset(CMAKE_CXX_COMPILER aarch64-linux-gnu-g++)\nset(CMAKE_SYSROOT /path/to/sysroot)\nset(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)\nset(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)\nset(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)\n
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    Configure with cmake -S . -B build -DCMAKE_TOOLCHAIN_FILE=aarch64.cmake. Done when: the build system resolves the cross compiler and searches only the sysroot for libraries.

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    7. \n

  7. Run under QEMU user mode: apt install qemu-user-static, then qemu-aarch64-static ./hello; with binfmt_misc registered the binary runs directly. Debug: qemu-aarch64-static -g 1234 ./hello & then aarch64-linux-gnu-gdb -ex \"target remote :1234\" ./hello. Done when: the binary runs or the debugger attaches.

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  8. Map errors from the table. Done when: each reported error has a cause and fix.

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    ErrorCauseFix
    cannot execute binary file: Exec format errorTarget binary run on the hostRun under qemu-<arch>-static
    wrong ELF class: ELFCLASS64 (or 32)Object from another architecture in the linkOne toolchain for every object; check AR and CC
    ld: cannot find -lfooHost library path used in a cross linkSet --sysroot; fix PKG_CONFIG_LIBDIR
    undefined reference to '__aeabi_*'ARM runtime helpers missing from a -nostdlib linkAdd -lgcc
    relocation ... out of rangeCode or data too far apart for the relocation-mcmodel=large or restructure
    unrecognized opcode-mcpu or -march does not match the sourceSet the CPU flags for the real target
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    9. \n
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Failure and recovery

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Failure classBehavior
No distribution package for the targetPoint to the vendor toolchain download; do not invent a package name.
Sysroot lacks a needed libraryReport the library as missing from the sysroot; the fix is to install it into the sysroot, not to use the host copy.
Windows target requestedUse the x86_64-w64-mingw32 triplet; MSVC-flavored builds: use msvc-cl.
No system cross toolchain wantedzig cc -target cross-compiles C without one: use zig-cross.
Assembly-level questionAArch64 or ARM assembly: use assembly-arm.
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Output

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A chat report with the triplet, install and confirmation commands, the compile command with target flags, sysroot and pkg-config settings when needed, the build-system wiring, the QEMU run or debug command, and the error table entries that apply. Flag details are in references/arm-flags.md.

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