Re: [PATCH v7] arm64: implement support for static call trampolines

[Peter Zijlstra]

On Fri, Mar 13, 2026 at 06:18:52AM +0000, Carlos Llamas wrote:
> From: Ard Biesheuvel <ardb@xxxxxxxxxx>
> 
> Implement arm64 support for the 'unoptimized' static call variety, which
> routes all calls through a single trampoline that is patched to perform a
> tail call to the selected function.
> 
> Since static call targets may be located in modules loaded out of direct
> branching range, we need to use a ADRP/ADD pair to load the branch target
> into R16 and use a branch-to-register (BR) instruction to perform an
> indirect call. Unlike on x86, there is no pressing need on arm64 to avoid
> indirect calls at all cost, but hiding it from the compiler as is done
> here does have some benefits:
> - the literal is located in .rodata, which gives us the same robustness
>   advantage that code patching does;
> - no performance hit on CFI enabled Clang builds that decorate compiler
>   emitted indirect calls with branch target validity checks.
> 
> Cc: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> Signed-off-by: Carlos Llamas <cmllamas@xxxxxxxxxx>

Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>