simple malloc and free using mmap

CMakeLists.txt

@@ -123,6 +123,7 @@ set(ZIG_STD_SRC
     "${CMAKE_SOURCE_DIR}/std/syscall.zig"
     "${CMAKE_SOURCE_DIR}/std/errno.zig"
     "${CMAKE_SOURCE_DIR}/std/rand.zig"
+    "${CMAKE_SOURCE_DIR}/std/mem.zig"
 )
 
 set(C_HEADERS_DEST "lib/zig/include")

std/mem.zig

@@ -0,0 +1,21 @@
+import "syscall.zig";
+import "std.zig";
+
+pub fn malloc(bytes: isize) -> ?&u8 {
+    if (bytes > 4096) {
+        %%stderr.printf("TODO alloc sizes > 4096B\n");
+        return null;
+    }
+
+    const result = mmap(0, 4096, MMAP_PROT_READ|MMAP_PROT_WRITE, MMAP_MAP_ANON|MMAP_MAP_SHARED, -1, 0);
+
+    if (result == -1) {
+        return null;
+    }
+
+    (&u8)(result)
+}
+
+pub fn free(ptr: &u8) {
+    munmap(isize(ptr), 4096);
+}

std/syscall.zig

@@ -1,8 +1,22 @@
 const SYS_read      = 0;
 const SYS_write     = 1;
+const SYS_mmap      = 9;
+const SYS_munmap    = 11;
 const SYS_exit      = 60;
 const SYS_getrandom = 318;
 
+// mmap constants
+pub const MMAP_PROT_NONE =  0;
+pub const MMAP_PROT_READ =  1;
+pub const MMAP_PROT_WRITE = 2;
+pub const MMAP_PROT_EXEC =  4;
+
+pub const MMAP_MAP_FILE =    0;
+pub const MMAP_MAP_SHARED =  1;
+pub const MMAP_MAP_PRIVATE = 2;
+pub const MMAP_MAP_FIXED =   16;
+pub const MMAP_MAP_ANON =    32;
+
 fn syscall1(number: isize, arg1: isize) -> isize {
     asm volatile ("syscall"
         : [ret] "={rax}" (-> isize)
@@ -17,6 +31,28 @@ fn syscall3(number: isize, arg1: isize, arg2: isize, arg3: isize) -> isize {
         : "rcx", "r11")
 }
 
+fn syscall2(number: isize, arg1: isize, arg2: isize) -> isize {
+    asm volatile ("syscall"
+        : [ret] "={rax}" (-> isize)
+        : [number] "{rax}" (number), [arg1] "{rdi}" (arg1), [arg2] "{rsi}" (arg2)
+        : "rcx", "r11")
+}
+
+fn syscall6(number: isize, arg1: isize, arg2: isize, arg3: isize, arg4: isize, arg5: isize, arg6: isize) -> isize {
+    asm volatile ("syscall"
+        : [ret] "={rax}" (-> isize)
+        : [number] "{rax}" (number), [arg1] "{rdi}" (arg1), [arg2] "{rsi}" (arg2), [arg3] "{rdx}" (arg3), [arg4] "{r10}" (arg4), [arg5] "{r8}" (arg5), [arg6] "{r9}" (arg6)
+        : "rcx", "r11")
+}
+
+pub fn mmap(address: isize, length: isize, prot: isize, flags: isize, fd: isize, offset: isize) -> isize {
+    syscall6(SYS_mmap, address, length, prot, flags, fd, offset)
+}
+
+pub fn munmap(address: isize, length: isize) -> isize {
+    syscall2(SYS_munmap, address, length)
+}
+
 pub fn read(fd: isize, buf: &u8, count: isize) -> isize {
     syscall3(SYS_read, isize(fd), isize(buf), count)
 }

test/run_tests.cpp

@@ -1344,6 +1344,24 @@ pub fn main(args: [][]u8) -> %void {
         %%stdout.printf("BAD\n");
     }
     %%stdout.printf("OK\n");
+}
+    )SOURCE", "OK\n");
+
+    add_simple_case("malloc and free", R"SOURCE(
+import "mem.zig";
+import "std.zig";
+
+pub fn main(args: [][]u8) -> %void {
+    var ptr = malloc(1) ?? unreachable{};
+
+    *ptr = 6;
+
+    if (*ptr != 6) {
+        %%stdout.printf("BAD\n");
+    }
+    %%stdout.printf("OK\n");
+
+    free(ptr);
 }
     )SOURCE", "OK\n");
 }