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Document Architecture Profile Test Macros #128

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31 changes: 31 additions & 0 deletions src/c-api.adoc
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Expand Up @@ -128,6 +128,37 @@ 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.

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+`.

The profile macro is defined (with value 1) when the compiler detects that the enabled extensions match a specific RISC-V profile.
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The word "match" leaves some room for interpretation:

  • Are the S* and H* extensions of a profile considered in the match?
  • What if additional extensions beyond those in the profile are enabled?
  • What if vendor extensions are enabled?

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@ZhongyaoChen ZhongyaoChen Oct 14, 2025 •
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Are the S* and H* extensions of a profile considered in the match?

Yes, if they are part of the profile definition.

What if additional extensions beyond those in the profile are enabled?

Additional extensions do not prevent a profile match. as long as all extensions required by the profile are present, this matched profile macro will be defined.

What if vendor extensions are enabled?

don't affect profile matching.


Example usage:

[source, C]
----
#ifdef __riscv_rva23u64
// Code specific to the RVA23U64 profile
#endif

#ifdef __riscv_rvi20u32
// Code specific to the RVI20U32 profile
#endif
----

NOTE: The compiler selects the best matching profile based on the maximum number of matching extensions when multiple profiles could apply.
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@topperc topperc Oct 14, 2025 •
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Doesn't this create a compatibility issue.

Developer writes code for RVA23U64 today.
In the future the code is compiled with RVA30U64 that is superset of RVA23U64. __riscv_rva23u64 macro is not defined because __riscv_rva30u64. Code no longer does the correct thing and must be updated to check for __riscv_rva30u64 OR __riscv_rva23u64.

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Thanks for the review, I do miss the compatibility issue.
maybe this better ? anyway, need reconsider the macro definitions.

#define __riscv_profile_number 23
#define __riscv_profile_class 'A'
#define __riscv_xlen 64

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#define __riscv_profile_class 'A'

https://github.com/riscv/riscv-profiles/blob/main/src/profiles.adoc#34-profile-naming-convention

Single letter might not work because spec say:

"A specific profile family name string. Initially a single letter (I, M, or A), but later profiles may have longer family name strings."

Also rvX30u64 might also a super-set of rva23u64...so I would prefer to define every profile macro if the extension meet the requirement of that profile.

That means -march=rva23s64 will define __riscv_rva23s64, __riscv_rva23u64, __riscv_rvi20u64, __riscv_rva20u64, __riscv_rva20s64, __riscv_rva22u64 and __riscv_rva22s64.

This seems little bit mess, but that could guarantee the code guarded with __riscv_rva23u64 could work on any future version which compatible with that.


=== ABI Related Preprocessor Definitions

.ABI Related Preprocessor Definitions
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