# How is TOOLCHAIN\_LD used?

**URL:** https://discourse.cmake.org/t/how-is-toolchain-ld-used/4841
**Category:** Usage
**Created:** [January 13, 2022, 12:29pm UTC](https://discourse.cmake.org/t/how-is-toolchain-ld-used/4841 "2022-01-13T12:29:56Z")
**Posts on this page:** 6
**Page:** 1

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### Author: ![DavidA](https://discourse.cmake.org/user_avatar/discourse.cmake.org/davida/32/128_2.png) [@DavidA](https://discourse.cmake.org/u/DavidA)
#### Post date: [January 13, 2022, 12:29pm UTC](https://discourse.cmake.org/t/how-is-toolchain-ld-used/4841/1 "2022-01-13T12:29:56Z")

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I am using the GNU ARM toolchain to cross-compile an ARM Cortex-M4 application on Windows.

In my toolchain file I have:

```auto
get_filename_component(TOOLCHAIN ${CROSS_GCC_PATH} PATH)
set(CMAKE_C_COMPILER ${TOOLCHAIN}/arm-none-eabi-gcc${SUFFIX})
set(CMAKE_Cxx_COMPILER ${TOOLCHAIN}/arm-none-eabi-g++${SUFFIX})
set(TOOLCHAIN_as ${TOOLCHAIN}/arm-none-eabi-as${SUFFIX} CACHE STRING "arm-none-eabi-as")
set(TOOLCHAIN_LD ${TOOLCHAIN}/arm-none-eabi-ld${SUFFIX} CACHE STRING "arm-none-eabi-ld")
set(TOOLCHAIN_SIZE ${TOOLCHAIN}/arm-none-eabi-size${SUFFIX} CACHE STRING "arm-none-eabi-size")

```

The resulting compiler command correctly uses **arm-none-eabi-gcc** but I find that the linker command also uses **arm-none-eabi-gcc** whereas I need it to call **arm-none-eabi-ld**.

Any ideas why please?

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### Author: ![fenrir](https://discourse.cmake.org/user_avatar/discourse.cmake.org/fenrir/32/734_2.png) [@fenrir](https://discourse.cmake.org/u/fenrir)
#### Post date: [January 13, 2022, 12:39pm UTC](https://discourse.cmake.org/t/how-is-toolchain-ld-used/4841/2 "2022-01-13T12:39:51Z")

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`TOOLCHAIN_*` are not variables used by CMake - they have no special meaning. See here: [https://cmake.org/cmake/help/latest/manual/cmake-variables.7.html](https://cmake.org/cmake/help/latest/manual/cmake-variables.7.html) for a list of recognised variables.

Additionally `CMAKE_Cxx_COMPILER` is misspelled - should be all upper case or you’re in for a surprise.

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### Author: ![DavidA](https://discourse.cmake.org/user_avatar/discourse.cmake.org/davida/32/128_2.png) [@DavidA](https://discourse.cmake.org/u/DavidA)
#### Post date: [January 13, 2022, 1:13pm UTC](https://discourse.cmake.org/t/how-is-toolchain-ld-used/4841/3 "2022-01-13T13:13:52Z")

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> [@fenrir](#):
>
> `TOOLCHAIN_*` are not variables used by CMake - they have no special meaning.

Thanks for your reply. I reworked my toolchain file to have:

```auto
set(CMAKE_C_COMPILER ${TOOLCHAIN}/arm-none-eabi-gcc${SUFFIX})
set(CMAKE_CXX_COMPILER ${TOOLCHAIN}/arm-none-eabi-g++${SUFFIX})
set(CMAKE_LINKER ${TOOLCHAIN}/arm-none-eabi-ld${SUFFIX} CACHE STRING "arm-none-eabi-ld")

```

but the linker command is still calling **arm-none-eabi-gcc** instead of **arm-none-eabi-ld**.

Any further thoughts please?

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<div class="post-metadata">

### Author: ![fenrir](https://discourse.cmake.org/user_avatar/discourse.cmake.org/fenrir/32/734_2.png) [@fenrir](https://discourse.cmake.org/u/fenrir)
#### Post date: [January 13, 2022, 1:28pm UTC](https://discourse.cmake.org/t/how-is-toolchain-ld-used/4841/4 "2022-01-13T13:28:43Z")

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Well, typically you just don’t and gcc will forward everything just right to the ld.  
If you really have to, I think you must adjust `CMAKE_LINKER` and `CMAKE_CXX_LINK_EXECUTABLE` as described here: [gcc - CMake: use a custom linker - Stack Overflow](https://stackoverflow.com/a/25274328/3114889)

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### Author: ![DavidA](https://discourse.cmake.org/user_avatar/discourse.cmake.org/davida/32/128_2.png) [@DavidA](https://discourse.cmake.org/u/DavidA)
#### Post date: [January 13, 2022, 2:37pm UTC](https://discourse.cmake.org/t/how-is-toolchain-ld-used/4841/5 "2022-01-13T14:37:33Z")

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The makefile that I am replacing explicitly calls arm-none-eabi-ld to do the linking so I think it best to do that.

I tried the suggestion from the Stack Overflow post:

`cmake -S .. -G "Unix Makefiles" -DCMAKE_TOOLCHAIN_FILE=toolchain-gnu-arm.cmake -DCMAKE_LINKER=/home/asic/lib/ARM/gcc-arm-none-eabi-10.3-2021.10/bin/arm-none-eabi-ld -DCMAKE_CXX_LINK_EXECUTABLE="<CMAKE_LINKER> <FLAGS> <CMAKE_CXX_LINK_FLAGS> <LINK_FLAGS> <OBJECTS> -o <TARGET> <LINK_LIBRARIES>"`

but CMake is still calling arm-none-eabi-gcc to do the link.

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<div class="post-metadata">

### Author: ![ben.boeckel](https://discourse.cmake.org/letter_avatar_proxy/v4/letter/b/ea5d25/32.png) [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [January 16, 2022, 6:01pm UTC](https://discourse.cmake.org/t/how-is-toolchain-ld-used/4841/6 "2022-01-16T18:01:41Z")

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> [@DavidA](#):
>
> but CMake is still calling arm-none-eabi-gcc to do the link.

CMake uses the compiler to drive the linker since it adds things like the standard library and other such things on its own. If CMake always used the linker, it would have to reverse engineer whatever flags get passed through the compiler driver.

> [@DavidA](#):
>
> The makefile that I am replacing explicitly calls arm-none-eabi-ld to do the linking so I think it best to do that.

Does using the compiler work? If so, just go with it. CMake does not offer fine-grained control over the linker because it is not well-abstracted at CMake level (between languages or generators).