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Explain entry/prefix values may be restricted 

Some existing codegens (notably ELFv2+GCC+PPC) can only do some values
of `prefix`/`entry`. Call out that it is possible for some values to
cause errors, even if the target/backend combination supports
patchability.
This commit is contained in:
Matthew Maurer 2024-01-23 22:37:31 +00:00
parent 6d1b0a2a21
commit 5c3fd167e3
1 changed files with 2 additions and 2 deletions
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@ -79,7 +79,7 @@ This flag sets the default nop padding for all functions in the crate. In most c
`prefix` is calculated as `offset`. `entry` is calculated as `nop_count - offset`. This unusual mode of specification is intended to mimic the compiler flags of `clang` and `gcc` for ease of build system integration.
Specifying the compiler flag for a backend or architecture which does not support this feature will result in an error.
Specifying the compiler flag for a backend or architecture which does not support this feature will result in an error. Some backend / architecture combinations may only support some values of `entry` and `prefix`, in which case an error will also be generated for invalid values.
## Attributes `#[patchable]` and `#[unpatchable]`.
@ -87,7 +87,7 @@ This attribute allows specification of either the `prefix` or `entry` values or
As this is specified via an attribute, it will persist across crate boundaries unlike the compiler flag.
Specifying any amount of padding other than 0 in an attribute will result in an error on backends or architectures which do not support this feature.
Specifying any amount of padding other than 0 in an attribute will result in an error on backends or architectures which do not support this feature. Some architecture/backend combinations may only support a subset of prefix and entry nop counts, and may generate errors when other counts are requested.
`#[unpatchable]` is a built-in alias for `#[patchable(prefix = 0, entry = 0)]`.