[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=45aaf8c6154298d3e00e8f6e1eb0558875a84121

commit 45aaf8c6154298d3e00e8f6e1eb0558875a84121
Author: Szabolcs Nagy <szabolcs.nagy@arm.com>
Date:   Wed Jan 6 11:31:04 2021 +0000

    Make libc symbols hidden in static PIE
    
    Hidden matters with static PIE: extern symbol access in position
    independent code usually involves GOT indirections which needs
    RELATIVE relocs in a static linked PIE. Using So hidden avoids
    indirections and RELATIVE relocs on targets that can access symbols
    pc-relative.
    
    The check should use IS_IN_LIB instead of IS_IN(libc) since all
    static libraries can use hidden visibility to avoid indirections,
    however the test system links objects from libcrypt.a into dynamic
    linked test binaries so hidden does not work there.  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.
    
    From -static-pie linked 'int main(){}' this shaves off 73 relative
    relocs on aarch64 and reduces code size too.

Diff:
---
 include/libc-symbols.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/libc-symbols.h b/include/libc-symbols.h
index ea126ae70c..93e63ee889 100644
--- a/include/libc-symbols.h
+++ b/include/libc-symbols.h
@@ -434,13 +434,17 @@ 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 && 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")))