libc-bottom-half/sources/sbrk.c

   1 #include <unistd.h>
   2 #include <stdlib.h>
   3 #include <errno.h>
   4 #include <__macro_PAGESIZE.h>
   5
   6 // Bare-bones implementation of sbrk.
   7 void *sbrk(intptr_t increment) {
   8     // sbrk(0) returns the current memory size.
   9     if (increment == 0) {
  10         // The wasm spec doesn't guarantee that memory.grow of 0 always succeeds.
  11         return (void *)(__builtin_wasm_memory_size(0) * PAGESIZE);
  12     }
  13
  14     // We only support page-size increments.
  15     if (increment % PAGESIZE != 0) {
  16         abort();
  17     }
  18
  19     // WebAssembly doesn't support shrinking linear memory.
  20     if (increment < 0) {
  21         abort();
  22     }
  23
  24     uintptr_t old = __builtin_wasm_memory_grow(0, (uintptr_t)increment / PAGESIZE);
  25
  26     if (old == SIZE_MAX) {
  27         errno = ENOMEM;
  28         return (void *)-1;
  29     }
  30
  31     return (void *)(old * PAGESIZE);
  32 }