diff --git a/src/codegen.cpp b/src/codegen.cpp
index 678433db5..7a2c95d1b 100644
--- a/src/codegen.cpp
+++ b/src/codegen.cpp
@@ -381,10 +381,10 @@ static LLVMValueRef fn_llvm_value(CodeGen *g, FnTableEntry *fn_table_entry) {
             LLVMSetLinkage(fn_table_entry->llvm_value, LLVMExternalLinkage);
             break;
         case GlobalLinkageIdWeak:
-            LLVMSetLinkage(fn_table_entry->llvm_value, LLVMWeakODRLinkage);
+            LLVMSetLinkage(fn_table_entry->llvm_value, LLVMWeakAnyLinkage);
             break;
         case GlobalLinkageIdLinkOnce:
-            LLVMSetLinkage(fn_table_entry->llvm_value, LLVMLinkOnceODRLinkage);
+            LLVMSetLinkage(fn_table_entry->llvm_value, LLVMLinkOnceAnyLinkage);
             break;
     }
 
diff --git a/std/debug.zig b/std/debug.zig
index af9bfe314..47f38748d 100644
--- a/std/debug.zig
+++ b/std/debug.zig
@@ -92,7 +92,8 @@ pub fn writeStackTrace(out_stream: &io.OutStream, allocator: &mem.Allocator, tty
                 const ptr_hex = if (@sizeOf(usize) == 4) "0x{x8}" else "0x{x16}";
 
                 const compile_unit = findCompileUnit(st, return_address) ?? {
-                    %return out_stream.print(DIM ++ ptr_hex ++ " in ??? (???)" ++ RESET ++ "\n\n\n", return_address);
+                    %return out_stream.print("???:?:?: " ++ DIM ++ ptr_hex ++ " in ??? (???)" ++ RESET ++ "\n    ???\n\n",
+                        return_address);
                     %return out_stream.flush();
                     continue;
                 };
diff --git a/std/os/index.zig b/std/os/index.zig
index 82db879f5..c0cb46b19 100644
--- a/std/os/index.zig
+++ b/std/os/index.zig
@@ -52,6 +52,7 @@ error ReadOnlyFileSystem;
 error LinkQuotaExceeded;
 error RenameAcrossMountPoints;
 error DirNotEmpty;
+error WouldBlock;
 
 /// Fills `buf` with random bytes. If linking against libc, this calls the
 /// appropriate OS-specific library call. Otherwise it uses the zig standard
@@ -128,6 +129,11 @@ pub fn posixClose(fd: i32) {
     }
 }
 
+error WouldBlock;
+error FileClosed;
+error DestinationAddressRequired;
+error FileSystem;
+
 /// Calls POSIX write, and keeps trying if it gets interrupted.
 pub fn posixWrite(fd: i32, bytes: []const u8) -> %void {
     while (true) {
@@ -136,12 +142,15 @@ pub fn posixWrite(fd: i32, bytes: []const u8) -> %void {
         if (write_err > 0) {
             return switch (write_err) {
                 errno.EINTR  => continue,
-                errno.EINVAL => unreachable,
+                errno.EINVAL, errno.EFAULT => unreachable,
+                errno.EAGAIN => error.WouldBlock,
+                errno.EBADF => error.FileClosed,
+                errno.EDESTADDRREQ => error.DestinationAddressRequired,
                 errno.EDQUOT => error.DiskQuota,
                 errno.EFBIG  => error.FileTooBig,
-                errno.EIO    => error.Io,
+                errno.EIO    => error.FileSystem,
                 errno.ENOSPC => error.NoSpaceLeft,
-                errno.EPERM  => error.BadPerm,
+                errno.EPERM  => error.AccessDenied,
                 errno.EPIPE  => error.PipeFail,
                 else         => error.Unexpected,
             }
@@ -185,7 +194,7 @@ pub fn posixOpen(file_path: []const u8, flags: usize, perm: usize, allocator: ?&
 
                 errno.EFAULT => unreachable,
                 errno.EINVAL => unreachable,
-                errno.EACCES => error.BadPerm,
+                errno.EACCES => error.AccessDenied,
                 errno.EFBIG, errno.EOVERFLOW => error.FileTooBig,
                 errno.EISDIR => error.IsDir,
                 errno.ELOOP => error.SymLinkLoop,
@@ -197,7 +206,7 @@ pub fn posixOpen(file_path: []const u8, flags: usize, perm: usize, allocator: ?&
                 errno.ENOMEM => error.SystemResources,
                 errno.ENOSPC => error.NoSpaceLeft,
                 errno.ENOTDIR => error.NotDir,
-                errno.EPERM => error.BadPerm,
+                errno.EPERM => error.AccessDenied,
                 else => error.Unexpected,
             }
         }
diff --git a/std/special/builtin.zig b/std/special/builtin.zig
index 26e5080d8..271b3936c 100644
--- a/std/special/builtin.zig
+++ b/std/special/builtin.zig
@@ -4,6 +4,7 @@
 // Note that these functions do not return `dest`, like the libc API.
 // The semantics of these functions is dictated by the corresponding
 // LLVM intrinsics, not by the libc API.
+const builtin = @import("builtin");
 
 export fn memset(dest: ?&u8, c: u8, n: usize) {
     @setDebugSafety(this, false);
@@ -31,5 +32,9 @@ export fn memcpy(noalias dest: ?&u8, noalias src: ?&const u8, n: usize) {
 }
 
 export fn __stack_chk_fail() {
+    if (builtin.is_release) {
+        @setGlobalLinkage(__stack_chk_fail, builtin.GlobalLinkage.Internal);
+        unreachable;
+    }
     @panic("stack smashing detected");
 }
diff --git a/std/special/zigrt.zig b/std/special/zigrt.zig
index 396a3b3cb..f5904050c 100644
--- a/std/special/zigrt.zig
+++ b/std/special/zigrt.zig
@@ -5,7 +5,7 @@
 const builtin = @import("builtin");
 
 export coldcc fn __zig_panic(message_ptr: &const u8, message_len: usize) -> noreturn {
-    @setGlobalLinkage(__zig_panic, builtin.GlobalLinkage.Weak);
+    @setGlobalLinkage(__zig_panic, builtin.GlobalLinkage.LinkOnce);
     @setDebugSafety(this, false);
 
     if (builtin.__zig_panic_implementation_provided) {