setjmp.h

// Copyright Microsoft and CHERIoT Contributors.
// SPDX-License-Identifier: MIT
#pragma once
 
/**
 * This is a minimal implementation of setjmp/longjmp.
 *
 * CHERIoT cannot store a `jmp_buf` anywhere other than the stack without
 * clearing tags (which will then cause `longjmp` to fail).
 */
 
#include <cdefs.h>
#include <stddef.h>
#include <stdint.h>
 
/**
 * Jump buffer for setjmp/longjmp.
 */
struct __jmp_buf
{
    uintptr_t __cs0;
    uintptr_t __cs1;
    uintptr_t __csp;
    uintptr_t __cra;
};
 
/**
 * C requires that `setjmp` and `longjmp` take a `jmp_buf` by reference and so
 * this ends up being defined as an array of one element, which allows it to
 * both be allocated and passed by reference.
 */
typedef struct __jmp_buf jmp_buf[1];
 
#include <setjmp-assembly.h>
 
__BEGIN_DECLS
/**
 * C `setjmp` function.  Returns (up to) twice.  First returns 0, returns a
 * value passed to `longjmp` on the second return.
 */
__attribute__((returns_twice)) int setjmp(jmp_buf env);
__asm__(".section .text.setjmp,\"awG\",@progbits,setjmp,comdat\n"
        ".globl setjmp\n"
        ".p2align 2\n"
        ".type setjmp,@function\n"
        "setjmp:\n"
        "   csc cs0, 0(ca0)\n"
        "   csc cs1, 8(ca0)\n"
        "   csc csp, 16(ca0)\n"
        "   csc cra, 24(ca0)\n"
        "   li  a0, 0\n"
        "   cret\n");
 
/**
 * C `longjmp` function.  Does not return, jumps back to the `setjmp` call.
 */
__attribute__((__noreturn__)) void longjmp(jmp_buf env, int val);
__asm__(".section .text.longjmp,\"awG\",@progbits,longjmp,comdat\n"
        ".globl longjmp\n"
        ".p2align 2\n"
        ".type longjmp,@function\n"
        "longjmp:\n"
        "   clc cs0, 0(ca0)\n"
        "   clc cs1, 8(ca0)\n"
        "   clc csp, 16(ca0)\n"
        "   clc cra, 24(ca0)\n"
        "   mv  a0, a1\n"
        "   cjr cra\n");
__END_DECLS