undefined behavior land

print.c

#include <stdio.h>

#define fmt(x) _Generic((x), \
  int:          "%d",        \
  long:         "%ld",       \
  float:        "%f",        \
  double:       "%lf",       \
  char:         "%c",        \
  char*:        "%s",        \
  const char*:  "%s",        \
  default:      "%p"         \
)

#define print_one(x) printf(fmt(x), x)

#define PRINT_1(a)         print_one(a)
#define PRINT_2(a,b)       print_one(a); print_one(b)
#define PRINT_3(a,b,c)     print_one(a); print_one(b); print_one(c)
#define PRINT_4(a,b,c,d)   print_one(a); print_one(b); print_one(c); print_one(d)
#define PRINT_5(a,b,c,d,e) print_one(a); print_one(b); print_one(c); print_one(d); print_one(e)

#define GET_MACRO(_1,_2,_3,_4,_5,NAME,...) NAME
#define print(...) GET_MACRO(__VA_ARGS__, PRINT_5,PRINT_4,PRINT_3,PRINT_2,PRINT_1)(__VA_ARGS__)

int main(void){
  print("This print works in c and does not care about types\n");

  char* name = "Pablo";
  int age = 67;

  print("this guy's name is ", name, " and he's ", age, " years old\n");
}

print2.c

#include <stdio.h>
#include <stdarg.h>
#include <stdint.h>
#include <signal.h>
#include <setjmp.h>

#define SENTINEL 0xDEADBEEFCAFEBABEULL

static sigjmp_buf probe_jmp;
static void probe_handler(int sig) { siglongjmp(probe_jmp, 1); }

static int can_read(uint64_t v) {
  struct sigaction sa = {
    .sa_handler = probe_handler
  }, old_bus, old_segv;
  
  sigaction(SIGBUS, &sa, &old_bus);
  sigaction(SIGSEGV, &sa, &old_segv);
  
  volatile int ok = 0;
  if (sigsetjmp(probe_jmp, 1) == 0) {
    (void)*(volatile char *)(uintptr_t)v;
    ok = 1;
  }
  
  sigaction(SIGBUS, &old_bus, NULL);
  sigaction(SIGSEGV, &old_segv, NULL);
  
  return ok;
}

__attribute__((noinline))
static void __print_inner(int dummy, ...) {
  enum { T_INT, T_STR, T_DBL, T_COUNT };

  va_list ap;
  va_start(ap, dummy);
  uint64_t *slot = (uint64_t *)(void *)ap;

  static const void *dispatch[] = {
    [T_INT] = &&l_int,
    [T_STR] = &&l_str,
    [T_DBL] = &&l_double,
  };

  while (*slot != SENTINEL) {
    uint64_t v = *slot++;
    uint8_t t = T_INT;
    
    if (v >= 0x1000 && v <= 0x0000ffffffffffff && can_read(v)) {
      unsigned char c = *(unsigned char *)(uintptr_t)v;
      if ((c >= 0x20 && c < 0x7f) || c == '\n' || c == '\t' || c == '\r' || c == '\0') t = T_STR;
    }
    
    if (t == T_INT && v > 0x7FFFFFFF) {
      uint64_t exp = (v >> 52) & 0x7FF;
      if (exp > 0 && exp < 0x7FF) t = T_DBL;
    }

    if (t < T_COUNT && dispatch[t]) goto *dispatch[t];
    continue;

    l_double: {
      double d;
      __builtin_memcpy(&d, &v, 8);
      printf("%g", d);
      continue;
    }
    
    l_int: printf("%d", (int)v); continue;
    l_str: printf("%s", (const char *)(uintptr_t)v); continue;
  }

  va_end(ap);
}

#define print(...) __print_inner(0, __VA_ARGS__, SENTINEL)

int main(void) {
  print("This print works in c and does not care about types\n");

  char *name = "Pablo";
  int age = 67;
  double pi = 3.14159;
  long big = 42L;

  print("name: ", name, " age: ", age, " pi: ", pi, " big: ", big, "\n");
}

print3.c

#include <stdio.h>
#include <stdarg.h>
#include <stdint.h>
#include <signal.h>
#include <setjmp.h>

#define SENTINEL 0xDEADBEEFCAFEBABEULL

static sigjmp_buf probe_jmp;
static void probe_handler(int sig) { siglongjmp(probe_jmp, 1); }


__attribute__((noinline))
static void __print_inner(int dummy, ...) {
  enum { T_INT, T_STR, T_DBL, T_COUNT };

  va_list ap;
  va_start(ap, dummy);
  uint64_t *slot = (uint64_t *)(void *)ap;

  static const void *dispatch[] = {
    [T_INT] = &&l_int,
    [T_STR] = &&l_str,
    [T_DBL] = &&l_double,
  };

  struct sigaction sa = {.sa_handler = probe_handler}, ob, os;
  sigaction(SIGBUS, &sa, &ob);
  sigaction(SIGSEGV, &sa, &os);

  while (*slot != SENTINEL) {
    uint64_t v = *slot++;
    uint8_t t = T_INT;
    
    if (sigsetjmp(probe_jmp, 1) == 0) {
      uint32_t is_str;
      __asm__ volatile(
        "ldrb %w[c], [%[ptr]]\n\t"
        "sub  %w[r], %w[c], #0x20\n\t"
        "cmp  %w[r], #0x5F\n\t"
        "cset %w[r], lo\n\t"
        "sub  %w[c], %w[c], #9\n\t"
        "cmp  %w[c], #5\n\t"
        "csinc %w[r], %w[r], %w[r], hs"
        : [r] "=&r"(is_str), [c] "=&r"((uint32_t){0})
        : [ptr] "r"((void*)(uintptr_t)v)
        : "cc", "memory"
      );
      if (is_str) t = T_STR;
    }
    
    if (t == T_INT && v > 0x7FFFFFFF) {
      uint32_t is_dbl;
      __asm__ volatile(
        "ubfx %w[e], %w[hi], #20, #11\n\t"
        "sub  %w[e], %w[e], #1\n\t"
        "cmp  %w[e], #0x7FE\n\t"
        "cset %w[e], lo"
        : [e] "=r"(is_dbl) : [hi] "r"((uint32_t)(v >> 32)) : "cc"
      );
      if (is_dbl) t = T_DBL;
    }
    
    if (t < T_COUNT) goto *dispatch[t];
    continue;

    l_str:    printf("%s", (const char *)(uintptr_t)v); continue;
    l_double: { double d; __builtin_memcpy(&d, &v, 8); printf("%g", d); continue; }
    l_int:    printf("%d", (int)v); continue;
  }

  sigaction(SIGBUS, &ob, NULL);
  sigaction(SIGSEGV, &os, NULL);
  va_end(ap);
}

#define print(...) __print_inner(0, __VA_ARGS__, SENTINEL)

int main(void) {
  print("This print works in c and does not care about types\n");

  char *name = "Pablo";
  int age = 67;
  double pi = 3.14159;
  long big = 42L;

  print("name: ", name, " age: ", age, " pi: ", pi, " big: ", big, "\n");
}

print4.c

#include <stdio.h>
#include <stdarg.h>
#include <stdint.h>
#include <signal.h>
#include <setjmp.h>

#define SENTINEL 0xDEADBEEFCAFEBABEULL
static sigjmp_buf jmp;
static void handler(int s) { siglongjmp(jmp, 1); }

static void _print(int d, ...) {
  va_list ap; va_start(ap, d);
  uint64_t *slot = (uint64_t *)(void *)ap;
  
  struct sigaction sa = {.sa_handler = handler}, ob, os;
  sigaction(SIGBUS, &sa, &ob); sigaction(SIGSEGV, &sa, &os);
  
  for (uint64_t v; (v = *slot++) != SENTINEL;) {
    int t = 0;
    if (!sigsetjmp(jmp, 1)) { 
      unsigned char c = *(char *)(uintptr_t)v; 
      t = (c - 9u < 5) || (c - 0x20u < 0x5F); 
    }
    
    if (!t && ((v >> 52 & 0x7FF) - 1u < 0x7FE)) t = 2;
    double f; __builtin_memcpy(&f, &v, 8);
    
    t == 1 
      ? printf("%s", (char *)(uintptr_t)v) 
      : t == 2 ? printf("%g", f) 
      : printf("%d", (int)v);
  }
  
  sigaction(SIGBUS, &ob, 0); sigaction(SIGSEGV, &os, 0);
}

#define print(...) _print(0, __VA_ARGS__, SENTINEL)

int main(void) {
  print("This print works in c and does not care about types\n");

  char *name = "Pablo";
  int age = 67;
  double pi = 3.14159;
  long big = 42L;

  print("name: ", name, " age: ", age, " pi: ", pi, " big: ", big, "\n");
}