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Document Architecture Profile Test Macros #128

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c0f6270
Document Architecture Profile Test Macros
ZhongyaoChen Oct 14, 2025
febba92
Document profile macro compatibility behavior
ZhongyaoChen Nov 21, 2025
4dbcbee
Clarify profile macros are optional
ZhongyaoChen Nov 21, 2025
6db8eeb
Add explicit value definition for profile macros
ZhongyaoChen Nov 22, 2025
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58 changes: 58 additions & 0 deletions src/c-api.adoc
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Expand Up @@ -128,6 +128,64 @@ For example:

- F-extension v2.2 will define `+__riscv_f+` as `2002000`.

=== Architecture Profile Test Macros

Architecture profile test macros allow checking whether a specific RISC-V profile
is in effect at compile-time. These macros enable developers to conditionally compile code
based on the target profile. These feature macros are optional, and compilers
that support them provide a `+__riscv_profile_test+` macro (with the value `1`).

The naming rule for profile test macros is `+__riscv_<profile_name>+`,
where `<profile_name>` is the lowercase profile identifier.

Examples:

- The test macro for the RVA23U64 profile is `+__riscv_rva23u64+`.
- The test macro for the RVI20U32 profile is `+__riscv_rvi20u32+`.

All profile test macros are defined with the value `1`:

[source, C]
----
#define __riscv_rva23u64 1
----

When a specific profile is targeted, the compiler defines not only the exact profile macro,
but also all compatible profile macros. This includes:

1. The exact profile macro for the targeted profile
2. Lower privilege mode variants (e.g., when targeting an S-mode profile, the corresponding U-mode profile macro is also defined, since S-mode is a superset of U-mode)
3. All previous compatible profile versions
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@topperc topperc Nov 21, 2025

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Does this include profiles that are compatible but not from the same profile family. Like RVI20 is subset of all defined RVA profiles.

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@ZhongyaoChen ZhongyaoChen Nov 21, 2025

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Yes


For example, when compiling with `-march=rva23s64`, the following macros are defined:

- `+__riscv_rva23s64+`
- `+__riscv_rva23u64+`
- `+__riscv_rva22s64+`
- `+__riscv_rva22u64+`
- `+__riscv_rva20s64+`
- `+__riscv_rva20u64+`
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@topperc topperc Nov 21, 2025 •
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So __rvi20u64 should be listed here?

Is rvb23s64/u64 also a subset of rva23s64?

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@ZhongyaoChen ZhongyaoChen Nov 21, 2025

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Yeah, __rvi20u64 should be there. Haven't checked rvb23, but I should add an ellipsis to show any profile with a subset of extensions should define its macro too.

- `+__riscv_rvi20u64+`
- ... (and any other profiles whose extension set is a subset)

This behavior ensures that code guarded with a profile macro will work correctly on any future
profile that is compatible with it, providing better forward compatibility and code portability.

Example usage:

[source, C]
----
#ifdef __riscv_rva23u64
// This code will execute on RVA23U64, RVA23S64, and any future
// profiles compatible with RVA23U64
#endif

#ifdef __riscv_rvi20u32
// This code will execute on RVI20U32 and any future
// profiles compatible with RVI20U32
#endif
----

=== ABI Related Preprocessor Definitions

.ABI Related Preprocessor Definitions
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