[glibc/nsz/bug27072] Make libc symbols hidden in static PIE

[Szabolcs Nagy <nsz@sourceware.org>]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=d7eb5cfd6953e9689c0306d808e234bd00741e6e

commit d7eb5cfd6953e9689c0306d808e234bd00741e6e
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Wed Jan 6 11:31:04 2021 +0000

    Make libc symbols hidden in static PIE
    
    Hidden visibility can avoid indirections and RELATIVE relocs in
    static PIE libc.
    
    The check should use IS_IN_LIB instead of IS_IN(libc) since all
    symbols are defined locally in static PIE and the optimization is
    useful in all libraries not just libc. However the test system
    links objects from libcrypt.a into dynamic linked test binaries
    where hidden visibility does not work.  I think mixing static and
    shared libc components in the same binary should not be supported
    usage, but to be safe only use hidden in libc.a.
    
    On some targets (i386) this optimization cannot be applied because
    hidden visibility PIE ifunc functions don't work, so it is gated by
    NO_HIDDEN_EXTERN_FUNC_IN_PIE.
    
    From -static-pie linked 'int main(){}' this shaves off 71 relative
    relocs on aarch64 and reduces code size by about 2k.

Diff:
---
 include/libc-symbols.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/include/libc-symbols.h b/include/libc-symbols.h
index ea126ae70c..f4dd735555 100644
--- a/include/libc-symbols.h
+++ b/include/libc-symbols.h
@@ -434,13 +434,18 @@ for linking")
   strong_alias(real, name)
 #endif
 
-#if defined SHARED || defined LIBC_NONSHARED \
-  || (BUILD_PIE_DEFAULT && IS_IN (libc))
+#if defined SHARED || defined LIBC_NONSHARED
 # define attribute_hidden __attribute__ ((visibility ("hidden")))
 #else
 # define attribute_hidden
 #endif
 
+/* Mark all symbols hidden in static PIE libc to avoid GOT indirections.  */
+#if BUILD_PIE_DEFAULT && !defined NO_HIDDEN_EXTERN_FUNC_IN_PIE \
+    && IS_IN (libc) && !defined LIBC_NONSHARED
+# pragma GCC visibility push(hidden)
+#endif
+
 #define attribute_tls_model_ie __attribute__ ((tls_model ("initial-exec")))
 
 #define attribute_relro __attribute__ ((section (".data.rel.ro")))