help with building STM32H735 demo project with clang

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I have a custom board with a STM32H735 and I have several issues with it building with clang and TouchGFX 4.26 for vscode. It works fine with 4.25 and GCC. I'm putting this migration on hold for now as many of these tools are still experimental.

What I now want is to first get a demo project working on the STM32H735G-DK board in vscode with cmake and clang.
I tried it this way:

1. in TouchGFX Designer 4.26 I select my board and select Dynamic Graph example. This builds and runs in Designer. 
2. I open the IOC file in STM32CubeMX V6.15.0 and change toolchain to CMake+Clang
3. I build in VScode using STM32Cube plugin (pre-release)
4. I get build errors

[main] Building folder: C:/TouchGFXProjects/MyApplication_24/build/Debug 
[build] Starting build
[driver] NOTE: You are building with preset Debug, but there are some overrides being applied from your VS Code settings.
[proc] Executing command: chcp
[proc] Executing command: cube-cmake --build C:/TouchGFXProjects/MyApplication_24/build/Debug --
[build] [1/132] Building C object CMakeFiles/STM32H735G-DK.dir/LIBJPEG/App/libjpeg.c.obj
...
[build] C:/TouchGFXProjects/MyApplication_24/Core/Src/main.c:545:23: warning: unused variable 'ospi_ram_init' [-Wunused-variable]
[build] 545 | BSP_OSPI_RAM_Init_t ospi_ram_init;
...
[build] C:\ST\STM32CubeCLT_1.19.0\GNU-tools-for-STM32\bin/../lib/gcc/arm-none-eabi/13.3.1/../../../../arm-none-eabi/bin/ld: STM32H735G-DK.elf section `TouchGFX_Framebuffer' will not fit in region `DTCMRAM'
[build] C:\ST\STM32CubeCLT_1.19.0\GNU-tools-for-STM32\bin/../lib/gcc/arm-none-eabi/13.3.1/../../../../arm-none-eabi/bin/ld: STM32H735G-DK.elf section `TouchGFX_Framebuffer' will not fit in region `FLASH'
[build] C:\ST\STM32CubeCLT_1.19.0\GNU-tools-for-STM32\bin/../lib/gcc/arm-none-eabi/13.3.1/../../../../arm-none-eabi/bin/ld: region `DTCMRAM' overflowed by 1542024 bytes
[build] C:\ST\STM32CubeCLT_1.19.0\GNU-tools-for-STM32\bin/../lib/gcc/arm-none-eabi/13.3.1/../../../../arm-none-eabi/bin/ld: region `FLASH' overflowed by 1256628 bytes
[build] Memory region         Used Size  Region Size  %age Used
[build]          DTCMRAM:     1673096 B       128 KB    1276.47%
[build]           RAM_D1:           0 B       320 KB      0.00%
[build]           RAM_D2:           0 B        32 KB      0.00%
[build]           RAM_D3:           0 B        16 KB      0.00%
[build]          ITCMRAM:           0 B        64 KB      0.00%
[build]            FLASH:     2305204 B         1 MB    219.84%
[build] starm-clang++: error: ld command failed with exit code 1 (use -v to see invocation)

Obviously one problem is the linker file here. I will try to merge this with the GCC linker file. It also seems ospi-ram is not used.

I've also tried to make the project starting from STM32CubeMX V6.15.0, but by default TouchGFX and all the needed peripherals are not configured. It's too much work to get it working from MX.

Why doesn't it work out of the box? Or am I doing something wrong?

UPDATE:

I've copied the linker file from the STM32CubeIDE project and now it builds. But I cannot flash/debug in vscode. I can only flash it from STM32CubeProgrammer.

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After copying the linker file from the unmodified STM32CubeIDE project to the clang project the build worked, but flashing/debugging failed. I had to add the following to launch.json to get debugging working. I switched to a different vscode profile, since the ST plugin doesn't work with cortex-debug.

        {
            "cwd": "${workspaceRoot}",
            "executable": "./build/Debug/STM32H735G-DK.elf",
            "name": "Debug with STLINK",
            "request": "launch",
            "type": "cortex-debug",
            "showDevDebugOutput": "raw",      
            "servertype": "stlink",
            "serverArgs": [
            "--extload", "C:\\ST\\STM32CubeCLT_1.19.0\\STM32CubeProgrammer\\bin\\ExternalLoader\\MX25LM51245G_STM32H735G-DK.stldr"         
            ],           
            "windows": {
            "serverpath": "C:/ST/STM32CubeCLT_1.19.0/STLink-gdb-server/bin/ST-LINK_gdbserver.exe",
            "stm32cubeprogrammer": "C:/ST/STM32CubeCLT_1.19.0/STM32CubeProgrammer/bin",
            "svdFile": "C:/ST/STM32CubeCLT_1.19.0/STMicroelectronics_CMSIS_SVD/STM32H735.svd"
            },       
            "runToEntryPoint": "main",  
        }

Now I'm having issues with clang-tidy. If I use clang-tidy from clang 1.19.5 I get the following issues:

PS C:\LLVM_19.1.5\bin> ./clang-tidy.exe -p C:\TouchGFXProjects\MyApplication_24\build\Debug C:\TouchGFXProjects\MyApplication_24\Core\Src\main.c
21 errors generated.
Error while processing C:\TouchGFXProjects\MyApplication_24\Core\Src\main.c.
error: too many errors emitted, stopping now [clang-diagnostic-error]
error: unknown argument: '--multi-lib-config=C:\ST\STM32CubeCLT_1.19.0\st-arm-clang/multilib.gnu_tools_for_stm32.yaml' [clang-diagnostic-error]
C:/TouchGFXProjects/MyApplication_24/cmake/stm32cubemx/../../Drivers/CMSIS/Include\cmsis_compiler.h:278:4: error: Unknown compiler. [clang-diagnostic-error]
278 | #error Unknown compiler.
| ^
C:/TouchGFXProjects/MyApplication_24/cmake/stm32cubemx/../../Drivers/CMSIS/Include\core_cm7.h:1871:1: error: unknown type name '__STATIC_INLINE' [clang-diagnostic-error]
1871 | __STATIC_INLINE void __NVIC_SetPriorityGrouping(uint32_t PriorityGroup)

Same for C:\LLVM_19.1.6 and C:\LLVM_21.1.4

And if I use clang-tidy from stm32cube\bundles\st-arm-clang\19.1.6+st.9:

.\starm-clang-tidy.exe -p C:\TouchGFXProjects\MyApplication_24\build\Debug C:\TouchGFXProjects\MyApplication_24\Core\Src\main.c
Error while processing C:/TouchGFXProjects/MyApplication_24/Core/Src/main.c.
error: unknown target triple 'unknown' [clang-diagnostic-error]
error: unsupported option '-mcpu=' for target '' [clang-diagnostic-error]
error: unsupported option '-mfloat-abi=' for target '' [clang-diagnostic-error]
error: unsupported option '-mfpu=' for target '' [clang-diagnostic-error]
warning: argument unused during compilation: '--gcc-toolchain=C:\ST\STM32CubeCLT_1.19.0\GNU-tools-for-STM32\bin/..' [clang-diagnostic-unused-command-line-argument]
warning: argument unused during compilation: '--multi-lib-config=C:\ST\STM32CubeCLT_1.19.0\st-arm-clang/multilib.gnu_tools_for_stm32.yaml' [clang-diagnostic-unused-command-line-argument]
Found compiler error(s).

And the same for clang-tidy from C:\ST\STM32CubeCLT_1.19.0\st-arm-clang\bin

Strangely I could not find the release of clang for arm 19.1.6 on github.  https://github.com/ARM-software/LLVM-embedded-toolchain-for-Arm/tags What version does ST base it on?

In summary these are the issues.:

• vscode + clang + cmake does not work out of the box with TouchGFX
• it requires modification of the linker file after converting it with STM32CubeMX
• debug/flashing doesn't work with STM32Cube plugin, it does work with cortex-debug plugin with a custom launch.json file
• clang-tidy doesn't work on the code