![]() ![]() The particular way this assembly does this is first copying the value from i to the output,įirst, we can see that asm! allows multiple template string arguments each This will add 5 to the input in variable i and write the result to variable o. Let us see another example that also uses an input: #! The template and will read the variable from there after the inline assembly finishes executing. The compiler will choose an appropriate register to insert into In this case we put it in an arbitrary general purpose register by specifying reg. We also need to specify in what kind of register the assembly expects the variable. First we need to specify if the variable is an input or an output of the The arguments that are inserted into the template however look a bit different than you mayīe familiar with. It is governed by the same rules as Rust. You can see that the string literal we use to specify instructions is actually a template string. This will write the value 5 into the u64 variable x. Now inserting an instruction that does nothing is rather boring. In the first argument of the asm! macro as a string literal. ![]() The instructions to be inserted are listed Note that all asm! invocations have to be inside an unsafe block, as they could insertĪrbitrary instructions and break various invariants. This will insert a NOP (no operation) instruction into the assembly generated by the compiler. Let us start with the simplest possible example: #! Inline assembly is currently supported on the following architectures: Note: the examples here are given in x86/x86-64 assembly, but other architectures are also supported. in kernel code, may also demand this functionality. Accessing low level hardware primitives, e.g. Generally this should not be necessary, but might be where the required performance or timingĬannot be otherwise achieved. It can be used to embed handwritten assembly in the assembly output generated by the compiler. Rust provides support for inline assembly via the asm! macro. ![]()
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