stack_x86_64.h

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/* -*- C -*-
 * Serene programming language
 * Copyright (C) 2019-2026 Sameer Rahmani <[email protected]>
 *
 * This library is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this library.  If not, see <https://www.gnu.org/licenses/>.
 */
 
#pragma once
 
#include <stddef.h>
#include <stdint.h>
 
/// Defined in switch_x86_64.S. Not callable from C; only its address is taken,
/// to seed the initial return address of a fresh fiber.
extern void srn_fiber_trampoline(void);
 
/// srn_fiber_frame is the exact frame srn_fiber_swap (switch_x86_64.S) pushes
/// and pops, and that srn_fiber_ctx_make (ctx_x86_64.c) fabricates for a fresh
/// fiber. Its field order and offsets ARE the contract with that assembly; the
/// static asserts pin them so the C side and the assembly cannot drift apart.
/// Only the matching x86-64 sources include this header.
typedef struct srn_fiber_frame {
  uint32_t mxcsr;     ///<  0  stmxcsr/ldmxcsr (%rsp)
  uint32_t _pad0;     ///<  4
  uint16_t fcw;       ///<  8  fnstcw/fldcw 8(%rsp)
  uint16_t _pad1;     ///< 10
  uint32_t _pad2;     ///< 12  rounds the FP control block to 16 bytes
  uintptr_t r15;      ///< 16
  uintptr_t r14;      ///< 24
  uintptr_t r13;      ///< 32  entry function
  uintptr_t r12;      ///< 40  entry argument
  uintptr_t rbx;      ///< 48
  uintptr_t rbp;      ///< 56
  uintptr_t ret_addr; ///< 64  resume address (= srn_fiber_trampoline)
} srn_fiber_frame_t;
 
// NOLINTBEGIN(readability-magic-numbers)
_Static_assert(sizeof(srn_fiber_frame_t) == 72,
               "srn_fiber_frame must match switch_x86_64.S");
_Static_assert(offsetof(srn_fiber_frame_t, fcw) == 8, "fcw offset");
_Static_assert(offsetof(srn_fiber_frame_t, r13) == 32, "r13 (fn) offset");
_Static_assert(offsetof(srn_fiber_frame_t, r12) == 40, "r12 (arg) offset");
_Static_assert(offsetof(srn_fiber_frame_t, ret_addr) == 64, "ret_addr offset");
// NOLINTEND(readability-magic-numbers)
 
/// SysV AMD64 requires 16-byte stack alignment at a call; srn_fiber_ctx_make
/// rounds the frame's base down to this so the trampoline's entry rsp is
/// aligned.
#define SRN_FIBER_STACK_ALIGN 16U
 
/// Control-register values a fresh fiber starts with: all FP exceptions masked,
/// round-to-nearest, extended precision -- the environment a freshly started C
/// program runs with. srn_fiber_ctx_make seeds them into the frame above.
///
/// SSE control/status word (MXCSR)
#define SRN_FIBER_MXCSR_DEFAULT 0x1F80U
/// x87 control word
#define SRN_FIBER_FCW_DEFAULT 0x037FU