mirror of
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e3424332d3
* `doc/langref` formatting
* upgrade `.{ .path = "..." }` to `b.path("...")`
* avoid using arguments named `self`
* make `Build.Step.Id` usage more consistent
* add `Build.pathResolve`
* use `pathJoin` and `pathResolve` everywhere
* make sure `Build.LazyPath.getPath2` returns an absolute path
61 lines
3.2 KiB
Zig
61 lines
3.2 KiB
Zig
pub fn syscall1(number: usize, arg1: usize) usize {
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// Inline assembly is an expression which returns a value.
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// the `asm` keyword begins the expression.
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return asm
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// `volatile` is an optional modifier that tells Zig this
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// inline assembly expression has side-effects. Without
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// `volatile`, Zig is allowed to delete the inline assembly
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// code if the result is unused.
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volatile (
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// Next is a comptime string which is the assembly code.
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// Inside this string one may use `%[ret]`, `%[number]`,
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// or `%[arg1]` where a register is expected, to specify
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// the register that Zig uses for the argument or return value,
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// if the register constraint strings are used. However in
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// the below code, this is not used. A literal `%` can be
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// obtained by escaping it with a double percent: `%%`.
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// Often multiline string syntax comes in handy here.
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\\syscall
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// Next is the output. It is possible in the future Zig will
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// support multiple outputs, depending on how
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// https://github.com/ziglang/zig/issues/215 is resolved.
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// It is allowed for there to be no outputs, in which case
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// this colon would be directly followed by the colon for the inputs.
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:
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// This specifies the name to be used in `%[ret]` syntax in
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// the above assembly string. This example does not use it,
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// but the syntax is mandatory.
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[ret]
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// Next is the output constraint string. This feature is still
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// considered unstable in Zig, and so LLVM/GCC documentation
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// must be used to understand the semantics.
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// http://releases.llvm.org/10.0.0/docs/LangRef.html#inline-asm-constraint-string
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// https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html
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// In this example, the constraint string means "the result value of
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// this inline assembly instruction is whatever is in $rax".
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"={rax}"
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// Next is either a value binding, or `->` and then a type. The
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// type is the result type of the inline assembly expression.
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// If it is a value binding, then `%[ret]` syntax would be used
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// to refer to the register bound to the value.
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(-> usize),
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// Next is the list of inputs.
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// The constraint for these inputs means, "when the assembly code is
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// executed, $rax shall have the value of `number` and $rdi shall have
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// the value of `arg1`". Any number of input parameters is allowed,
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// including none.
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: [number] "{rax}" (number),
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[arg1] "{rdi}" (arg1),
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// Next is the list of clobbers. These declare a set of registers whose
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// values will not be preserved by the execution of this assembly code.
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// These do not include output or input registers. The special clobber
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// value of "memory" means that the assembly writes to arbitrary undeclared
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// memory locations - not only the memory pointed to by a declared indirect
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// output. In this example we list $rcx and $r11 because it is known the
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// kernel syscall does not preserve these registers.
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: "rcx", "r11"
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);
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}
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// syntax
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