diff mbox series

[v2,2/4] Make libc symbols hidden in static PIE

Message ID 56297d0f9c00bd27901dc41ef20d749cf564def7.1610121077.git.szabolcs.nagy@arm.com
State New
Headers show
Series fix ifunc with static pie [BZ #27072] | expand

Commit Message

Szabolcs Nagy Jan. 8, 2021, 4:20 p.m. UTC 
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.
---
 include/libc-symbols.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)
diff mbox series

Patch

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")))