1 files changed, 32 insertions, 0 deletions
diff --git a/libc-bottom-half/sources/sbrk.c b/libc-bottom-half/sources/sbrk.c
new file mode 100644
index 0000000..a26b75e
--- /dev/null
+++ b/libc-bottom-half/sources/sbrk.c
@@ -0,0 +1,32 @@
+#include <unistd.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <__macro_PAGESIZE.h>
+
+// Bare-bones implementation of sbrk.
+void *sbrk(intptr_t increment) {
+    // sbrk(0) returns the current memory size.
+    if (increment == 0) {
+        // The wasm spec doesn't guarantee that memory.grow of 0 always succeeds.
+        return (void *)(__builtin_wasm_memory_size(0) * PAGESIZE);
+    }
+
+    // We only support page-size increments.
+    if (increment % PAGESIZE != 0) {
+        abort();
+    }
+
+    // WebAssembly doesn't support shrinking linear memory.
+    if (increment < 0) {
+        abort();
+    }
+
+    uintptr_t old = __builtin_wasm_memory_grow(0, (uintptr_t)increment / PAGESIZE);
+
+    if (old == SIZE_MAX) {
+        errno = ENOMEM;
+        return (void *)-1;
+    }
+
+    return (void *)(old * PAGESIZE);
+}