kit

kit
git clone https://git.ryansepassi.com/git/kit.git
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crt.c (1457B)

      1 /* Freestanding entry point for the bounce harness.
      2  *
      3  * The harness compiles this with a -DBOUNCE_<ARCH> define selecting the
      4  * guest architecture (kit does not predefine __x86_64__ etc.).  _start
      5  * calls bounce_main with a normal C call so the compiler emits the proper
      6  * cross-translation-unit relocation — the very edge the format-bounce
      7  * exercises — then exits via exit_group with its return value.
      8  *
      9  * The syscall is set up with explicit `mov` instructions taking the exit
     10  * code through a generic "r" operand rather than GCC local register
     11  * variables (which kit does not honor) or per-arch call/syscall pseudos
     12  * (which the standalone assembler does not model). */
     13 
     14 int bounce_main(void);
     15 
     16 __attribute__((noreturn)) static void sys_exit(int code) {
     17 #if defined(BOUNCE_X64)
     18   __asm__ volatile(
     19       "movl %0, %%edi\n\t"
     20       "movl $231, %%eax\n\t" /* exit_group */
     21       "syscall\n\t"
     22       :
     23       : "r"(code)
     24       : "eax", "edi", "memory");
     25 #elif defined(BOUNCE_AARCH64)
     26   __asm__ volatile(
     27       "mov x0, %0\n\t"
     28       "mov x8, #94\n\t"
     29       "svc #0\n\t"
     30       :
     31       : "r"((long)code)
     32       : "x0", "x8", "memory");
     33 #elif defined(BOUNCE_RV64)
     34   __asm__ volatile(
     35       "mv a0, %0\n\t"
     36       "li a7, 94\n\t"
     37       "ecall\n\t"
     38       :
     39       : "r"((long)code)
     40       : "a0", "a7", "memory");
     41 #else
     42 #error "define BOUNCE_X64 / BOUNCE_AARCH64 / BOUNCE_RV64"
     43 #endif
     44   for (;;) {
     45   }
     46 }
     47 
     48 void _start(void) { sys_exit(bounce_main()); }