Zig code
{#syntax_block|zig|call_malloc_from_zig.zig#} // malloc prototype included for reference -extern fn malloc(size: size_t) ?*u8; +extern fn malloc(size: usize) ?*u8; fn doAThing() ?*Foo { const ptr = malloc(1234) orelse return null; @@ -7479,64 +7478,66 @@ pub fn syscall3(number: usize, arg1: usize, arg2: usize, arg3: usize) usize {Dissecting the syntax:
- {#syntax_block|zig|Assembly Syntax Explained#} -// Inline assembly is an expression which returns a value. -// the `asm` keyword begins the expression. -_ = asm -// `volatile` is an optional modifier that tells Zig this -// inline assembly expression has side-effects. Without -// `volatile`, Zig is allowed to delete the inline assembly -// code if the result is unused. -volatile ( -// Next is a comptime string which is the assembly code. -// Inside this string one may use `%[ret]`, `%[number]`, -// or `%[arg1]` where a register is expected, to specify -// the register that Zig uses for the argument or return value, -// if the register constraint strings are used. However in -// the below code, this is not used. A literal `%` can be -// obtained by escaping it with a double percent: `%%`. -// Often multiline string syntax comes in handy here. + {#code_begin|syntax|Assembly Syntax Explained#} +pub fn syscall1(number: usize, arg1: usize) usize { + // Inline assembly is an expression which returns a value. + // the `asm` keyword begins the expression. + return asm + // `volatile` is an optional modifier that tells Zig this + // inline assembly expression has side-effects. Without + // `volatile`, Zig is allowed to delete the inline assembly + // code if the result is unused. + volatile ( + // Next is a comptime string which is the assembly code. + // Inside this string one may use `%[ret]`, `%[number]`, + // or `%[arg1]` where a register is expected, to specify + // the register that Zig uses for the argument or return value, + // if the register constraint strings are used. However in + // the below code, this is not used. A literal `%` can be + // obtained by escaping it with a double percent: `%%`. + // Often multiline string syntax comes in handy here. \\syscall -// Next is the output. It is possible in the future Zig will -// support multiple outputs, depending on how -// https://github.com/ziglang/zig/issues/215 is resolved. -// It is allowed for there to be no outputs, in which case -// this colon would be directly followed by the colon for the inputs. - : -// This specifies the name to be used in `%[ret]` syntax in -// the above assembly string. This example does not use it, -// but the syntax is mandatory. - [ret] -// Next is the output constraint string. This feature is still -// considered unstable in Zig, and so LLVM/GCC documentation -// must be used to understand the semantics. -// http://releases.llvm.org/10.0.0/docs/LangRef.html#inline-asm-constraint-string -// https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html -// In this example, the constraint string means "the result value of -// this inline assembly instruction is whatever is in $rax". - "={rax}" -// Next is either a value binding, or `->` and then a type. The -// type is the result type of the inline assembly expression. -// If it is a value binding, then `%[ret]` syntax would be used -// to refer to the register bound to the value. - (-> usize) -// Next is the list of inputs. -// The constraint for these inputs means, "when the assembly code is -// executed, $rax shall have the value of `number` and $rdi shall have -// the value of `arg1`". Any number of input parameters is allowed, -// including none. - : [number] "{rax}" (number), - [arg1] "{rdi}" (arg1) -// Next is the list of clobbers. These declare a set of registers whose -// values will not be preserved by the execution of this assembly code. -// These do not include output or input registers. The special clobber -// value of "memory" means that the assembly writes to arbitrary undeclared -// memory locations - not only the memory pointed to by a declared indirect -// output. In this example we list $rcx and $r11 because it is known the -// kernel syscall does not preserve these registers. - : "rcx", "r11" -); - {#end_syntax_block#} + // Next is the output. It is possible in the future Zig will + // support multiple outputs, depending on how + // https://github.com/ziglang/zig/issues/215 is resolved. + // It is allowed for there to be no outputs, in which case + // this colon would be directly followed by the colon for the inputs. + : + // This specifies the name to be used in `%[ret]` syntax in + // the above assembly string. This example does not use it, + // but the syntax is mandatory. + [ret] + // Next is the output constraint string. This feature is still + // considered unstable in Zig, and so LLVM/GCC documentation + // must be used to understand the semantics. + // http://releases.llvm.org/10.0.0/docs/LangRef.html#inline-asm-constraint-string + // https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html + // In this example, the constraint string means "the result value of + // this inline assembly instruction is whatever is in $rax". + "={rax}" + // Next is either a value binding, or `->` and then a type. The + // type is the result type of the inline assembly expression. + // If it is a value binding, then `%[ret]` syntax would be used + // to refer to the register bound to the value. + (-> usize) + // Next is the list of inputs. + // The constraint for these inputs means, "when the assembly code is + // executed, $rax shall have the value of `number` and $rdi shall have + // the value of `arg1`". Any number of input parameters is allowed, + // including none. + : [number] "{rax}" (number), + [arg1] "{rdi}" (arg1) + // Next is the list of clobbers. These declare a set of registers whose + // values will not be preserved by the execution of this assembly code. + // These do not include output or input registers. The special clobber + // value of "memory" means that the assembly writes to arbitrary undeclared + // memory locations - not only the memory pointed to by a declared indirect + // output. In this example we list $rcx and $r11 because it is known the + // kernel syscall does not preserve these registers. + : "rcx", "r11" + ); +} + {#code_end#}For x86 and x86_64 targets, the syntax is AT&T syntax, rather than the more popular Intel syntax. This is due to technical constraints; assembly parsing is @@ -7892,7 +7893,7 @@ fn add(a: i32, b: i32) i32 { {#syntax#}@call{#endsyntax#} allows more flexibility than normal function call syntax does. The {#syntax#}CallModifier{#endsyntax#} enum is reproduced here:
- {#syntax_block|zig|builtin.CallModifier struct#} + {#code_begin|syntax|builtin.CallModifier struct#} pub const CallModifier = enum { /// Equivalent to function call syntax. auto, @@ -7926,7 +7927,7 @@ pub const CallModifier = enum { /// compile-time, a compile error is emitted instead. compile_time, }; - {#end_syntax_block#} + {#code_end#} {#header_close#} {#header_open|@cDefine#}