make start code more versatile

 * always align the stack to 16. I saw an instance on x86_64 linux where
   it was needed.

 * detect at runtime if being interpreted by a dynamic loader and if so
   avoid clobbering the fs register.

1 files changed, 7 insertions, 1 deletions

diff --git a/lib/std/dynamic_library.zig b/lib/std/dynamic_library.zig
index 6c99ee644b..68181e5742 100644
--- a/lib/std/dynamic_library.zig
+++ b/lib/std/dynamic_library.zig
@@ -59,8 +59,14 @@ const RDebug = extern struct {
     r_ldbase: usize,
 };
 
+/// TODO make it possible to reference this same external symbol 2x so we don't need this
+/// helper function.
+pub fn get_DYNAMIC() ?[*]elf.Dyn {
+    return @extern([*]elf.Dyn, .{ .name = "_DYNAMIC", .linkage = .Weak });
+}
+
 pub fn linkmap_iterator(phdrs: []elf.Phdr) !LinkMap.Iterator {
-    const _DYNAMIC = @extern([*]elf.Dyn, .{ .name = "_DYNAMIC", .linkage = .Weak }) orelse {
+    const _DYNAMIC = get_DYNAMIC() orelse {
         // No PT_DYNAMIC means this is either a statically-linked program or a
         // badly corrupted dynamically-linked one.
         return LinkMap.Iterator{ .current = null };