ctx_x86_64.c File Reference

x86-64 fabrication of a fresh fiber's saved context. More...

#include <stdint.h>
#include "serene/rt/fiber.h"
#include "serene/rt/fiber/arch/stack_x86_64.h"

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Functions
void	srn_fiber_ctx_make (srn_fiber_ctx_t *fiber_ctx, srn_fiber_stack_t stack, void(*fn)(void *), void *arg)
	Initialise a fresh fiber context so the first srn_fiber_swap into it begins executing fn(arg) on stack.

Detailed Description

x86-64 fabrication of a fresh fiber's saved context.

Paired with switch_x86_64.S; both are selected by CPU family in meson.build.

Definition in file ctx_x86_64.c.

Function Documentation

srn_fiber_ctx_make()

void srn_fiber_ctx_make	(	srn_fiber_ctx_t *	fiber_ctx,
		srn_fiber_stack_t	stack,
		void(*	fn )(void *),
		void *	arg )

Initialise a fresh fiber context so the first srn_fiber_swap into it begins executing fn(arg) on stack.

fn is the fiber's entry: a void (*)(void *) that runs on the new stack and receives arg. It must NEVER return – there is no frame beneath it, so a return traps in the trampoline. Instead it transfers control away with srn_fiber_switch (to yield) or srn_fiber_switch_final (when finished), and as its first action it calls srn_fiber_on_entry(). Typical shape:

static void worker(void *arg) { srn_fiber_on_entry(&scheduler); // hand the switch to the sanitizer ... do the fiber's work using arg ... srn_fiber_switch_final(&scheduler); // finished, never returns }

Definition at line 29 of file ctx_x86_64.c.

                                   {
  // Lay srn_fiber_swap's frame (see rt/fiber/stack.h and switch_x86_64.S) at
  // the top of `stack`, rounded down to SRN_FIBER_STACK_ALIGN so the
  // return-address slot -- and thus the trampoline's entry rsp -- is correctly
  // aligned. The compound literal zero-fills the slots not named here. Register
  // slots are uintptr_t, so storing fn/trampoline is a
  // function-pointer-to-integer conversion (allowed), not the
  // function-to-object-pointer conversion that -Wpedantic forbids.
  uintptr_t top = (uintptr_t)stack.start;
  uintptr_t sp = (top - sizeof(srn_fiber_frame_t)) & ~(uintptr_t)(SRN_FIBER_STACK_ALIGN - 1);
 
  *(srn_fiber_frame_t *)sp = (srn_fiber_frame_t){
      .mxcsr = SRN_FIBER_MXCSR_DEFAULT,
      .fcw = SRN_FIBER_FCW_DEFAULT,
      .r13 = (uintptr_t)fn,
      .r12 = (uintptr_t)arg,
      .ret_addr = (uintptr_t)srn_fiber_trampoline,
  };
 
  fiber_ctx->sp = (void *)sp;
}

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