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Jonathon Penix (jonathonpenix) merged 2 commits into from
Mar 11, 2026
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[cpullvm] Add basic information about multilib #255

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[cpullvm] Add basic information about multilib
jonathonpenix Mar 11, 2026
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fixup! [cpullvm] Add basic information about multilib
jonathonpenix Mar 11, 2026
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4 changes: 4 additions & 0 deletions qualcomm-software/README.md
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Expand Up @@ -49,4 +49,8 @@ CPULLVM is built and tested on

Binary releases of CPULLVM are available [here](https://github.com/qualcomm/cpullvm-toolchain/releases).

For tips on getting started with using CPULLVM, please see [user.md](./docs/user.md).

For instructions on building from source, please see [building.md](./docs/building.md).
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If you are interested in contributing to CPULLVM, please see [CONTRIBUTING.md](/CONTRIBUTING.md).
27 changes: 27 additions & 0 deletions qualcomm-software/docs/user.md
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Expand Up @@ -24,3 +24,30 @@ supported include:
* RTTI

If variants with exceptions and RTTI enabled are required, please file an issue.

## Multilib
CPULLVM automatically selects a set of headers and runtime libraries to use when compiling and linking based on
the set of arguments passed on the command line. A warning will be emitted if no appropriate set of headers/libraries
can be found.

@apazos Ana Pazos (apazos) Mar 11, 2026

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can the warning be suppressed if build has to be clean of warnings, please indicate how

@jonathonpenix Jonathon Penix (jonathonpenix) Mar 11, 2026

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It works the same as any other warning.

I'm hesitant to put it here--people should not be disabling this unless they know what they're up to, at which point they should be able to figure out how to turn the warning off.

@apazos Ana Pazos (apazos) Mar 11, 2026

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this might be information useful in the migration guide - please if you do not want to add it here, share it with CE team


When compiling and linking, you should provide at least the following options on the command line:
* The target triple (ex: `--target=riscv32-unknown-elf`)
* `-march`, `-mabi`, and `-mfpu`, if using non-default options and applicable to your target
* Whether to use position independent code
* Any additional options like sanitizers or `-mbranch-protection`

Additionally, CPULLVM implements custom multilib flags to allow selecting variants that are not otherwise tied
to normal compiler flags. These are specified by `-fmultilib-flag=<flag>`. Currently implemented flags include:
* **`threads`/`nothreads`**: Picolibc only. When `threads` is set, a variant with [`thread-local-storage`](https://github.com/picolibc/picolibc/blob/ce4e736ebef081d13a81a29b6cfb51335f6f890d/doc/build.md#thread-local-storage-options) enabled,
[`single-thread`](https://github.com/picolibc/picolibc/blob/ce4e736ebef081d13a81a29b6cfb51335f6f890d/doc/build.md#locking-options) disabled,
and [`atomic-ungetc`](https://github.com/picolibc/picolibc/blob/ce4e736ebef081d13a81a29b6cfb51335f6f890d/doc/build.md#locking-options) enabled is selected. `nothreads` selects a variant with the inverse. `threads` is default.

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To display all available multilibs run clang with the flag `-print-multi-lib` and an appropriate target triple.

To display the directory selected by the multilib system, add the flag `-print-multi-directory` to your clang command line options.

> [!WARNING]
> Using `--sysroot` to select a variant or hardcoding paths to variants should generally not be done.
> Please file an issue if you find that this is needed.
>
> Variant names and paths may change at any time without notice.
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