Ensure __set_errno is still visible on LP32.

The use of the .hidden directive to avoid going via the PLT for
__set_errno had the side-effect of actually making __set_errno
hidden (which is odd because assembler directives don't usually
affect symbols defined in a different file --- you can't even
create a weak reference to a symbol that's defined in a different
file).

This change switches the system call stubs over to a new always-hidden
__set_errno_internal and has a visible __set_errno on LP32 just for
binary compatibility with old NDK apps.

Bug: 17423135
Change-Id: I6b6d7a05dda85f923d22e5ffd169a91e23499b7b

1 files changed, 12 insertions, 6 deletions

diff --git a/libc/bionic/__set_errno.cpp b/libc/bionic/__set_errno.cpp
index 236aeacee..30df350ea 100644
--- a/libc/bionic/__set_errno.cpp
+++ b/libc/bionic/__set_errno.cpp
@@ -36,14 +36,20 @@
 // system these are the same size, but on a 64-bit system they're not.
 // 'long' gives us 32-bit on 32-bit systems, 64-bit on 64-bit systems.
 
-#if __LP64__
-extern "C" __LIBC_HIDDEN__ long __set_errno(int);
-#else
 // __set_errno was mistakenly exposed in <errno.h> in the 32-bit NDK.
-extern "C" long __set_errno(int);
-#endif
+// We need the extra level of indirection so that the .hidden directives
+// in the system call stubs don't cause __set_errno to be hidden, breaking
+// old NDK apps.
 
-long __set_errno(int n) {
+// This one is for internal use only and used by both LP32 and LP64 assembler.
+extern "C" __LIBC_HIDDEN__ long __set_errno_internal(int n) {
   errno = n;
   return -1;
 }
+
+// This one exists for the LP32 NDK and is not present at all in LP64.
+#if !defined(__LP64__)
+extern "C" long __set_errno(int n) {
+  return __set_errno_internal(n);
+}
+#endif