Add a test case

std/os/linux/test.zig

@@ -1,6 +1,8 @@
 const std = @import("../../std.zig");
 const builtin = @import("builtin");
 const linux = std.os.linux;
+const mem = std.mem;
+const elf = std.elf;
 const expect = std.testing.expect;
 
 test "getpid" {
@@ -42,3 +44,42 @@ test "timer" {
     // TODO implicit cast from *[N]T to [*]T
     err = linux.epoll_wait(@intCast(i32, epoll_fd), @ptrCast([*]linux.epoll_event, &events), 8, -1);
 }
+
+export fn iter_fn(info: *linux.dl_phdr_info, size: usize, data: ?*usize) i32 {
+    var counter = data.?;
+    // Count how many libraries are loaded
+    counter.* += usize(1);
+
+    // The image should contain at least a PT_LOAD segment
+    if (info.dlpi_phnum < 1) return -1;
+
+    // Quick & dirty validation of the phdr pointers, make sure we're not
+    // pointing to some random gibberish
+    var i: usize = 0;
+    var found_load = false;
+    while (i < info.dlpi_phnum) : (i += 1) {
+        const phdr = info.dlpi_phdr[i];
+
+        if (phdr.p_type != elf.PT_LOAD) continue;
+
+        // Find the ELF header
+        const elf_header = @intToPtr(*elf.Ehdr, phdr.p_vaddr - phdr.p_offset);
+        // Validate the magic
+        if (!mem.eql(u8, elf_header.e_ident[0..], "\x7fELF")) return -1;
+        // Consistency check
+        if (elf_header.e_phnum != info.dlpi_phnum) return -1;
+
+        found_load = true;
+        break;
+    }
+
+    if (!found_load) return -1;
+
+    return 42;
+}
+
+test "dl_iterate_phdr" {
+    var counter: usize = 0;
+    expect(linux.dl_iterate_phdr(usize, iter_fn, &counter) != 0);
+    expect(counter != 0);
+}