commit

Pointer Authentication

Branch Target Identification

Memory Tagging Extension

AAPCS64 -> ARM Architecture Procedure Call Standard for 64-bit

These routines can be used for error handling recovery, and are included in <setjmp.h>

Saves the current execution context into a variable of type jmp_buf. It returns 0 on the first call, and a value different from zero if program control is restored with longjmp.

impl

Loads the execution context env saved by a previous call to setjmp. If the function that called setjmp has exited, the behavior is undefined (in other words, only long jumps up the call stack are allowed).

impl

GODBOLT

#include <math.h>
#include <setjmp.h>
#include <stdio.h>

typedef enum { DIV_BY_ZERO = 1 } division_exceptions;

jmp_buf divide_exception_h;

float divide(float x, float y) {
  if (y < 1e-6) {
    longjmp(divide_exception_h, DIV_BY_ZERO);
  }

  return x / y;
}

int main(int argc, char **argv) {
  switch (setjmp(divide_exception_h)) {
  case 0:
    float a = 1.0f;
    float b = 2.0f;
    float r = divide(a, b);
    printf("%f = %f / %f\n", r, a, b);
    break;
  case DIV_BY_ZERO:
    printf("Cannot divide by zero...\n");
    break;
  }

  switch (setjmp(divide_exception_h)) {
  case 0:
    float a = 1.0f;
    float b = 0.0f;
    float r = divide(a, b);
    printf("%f = %f / %f\n", r, a, b);
    break;
  case DIV_BY_ZERO:
    printf("Cannot divide by zero...\n");
    break;
  }

  return 0;
}

Special care is taken with X18 register which is reserved as a platform register.

jmp_buf is defined at src. Which stores register states.

TODO: investigate on add_entrypoint_object cmake

[[gnu::naked]] attribute

Use this attribute on the ARM, AVR, MCORE, MSP430, NDS32, RL78, RX and SPU ports to indicate that the specified function does not need prologue/epilogue sequences generated by the compiler. It is up to the programmer to provide these sequences. The only statements that can be safely included in naked functions are asm statements that do not have operands. All other statements, including declarations of local variables, if statements, and so forth, should be avoided. Naked functions should be used to implement the body of an assembly function, while allowing the compiler to construct the requisite function declaration for the assembler.

Attributes reference