Use hidden visibility for early static PIE code

Extern symbol access in position independent code usually involves GOT
indirection which needs RELATIVE reloc in a static linked PIE. (On
some targets this is avoided e.g. because the linker can relax a GOT
access to a pc-relative access, but this is not generally true.) Code
that runs before static PIE self relocation must avoid relying on
dynamic relocations which can be ensured by using hidden visibility.
However we cannot just make all symbols hidden:

On i386, all calls to IFUNC functions must go through PLT and calls to
hidden functions CANNOT go through PLT in PIE since EBX used in PIE PLT
may not be set up for local calls to hidden IFUNC functions.

This patch aims to make symbol references hidden in code that is used
before and by _dl_relocate_static_pie when building a static PIE libc.
Note: for an object that is used in the startup code, its references
and definition may not have consistent visibility: it is only forced
hidden in the startup code.

This is needed for fixing bug 27072.

Co-authored-by: H.J. Lu <hjl.tools@gmail.com>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

8 files changed, 34 insertions, 0 deletions

diff --git a/csu/libc-start.c b/csu/libc-start.c
index 5b9ce1d..a2f6e12 100644
--- a/csu/libc-start.c
+++ b/csu/libc-start.c
@@ -15,6 +15,10 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
+/* Mark symbols hidden in static PIE for early self relocation to work.  */
+#if BUILD_PIE_DEFAULT
+# pragma GCC visibility push(hidden)
+#endif
 #include <assert.h>
 #include <stdlib.h>
 #include <stdio.h>
diff --git a/elf/dl-reloc-static-pie.c b/elf/dl-reloc-static-pie.c
index a8d9640..d5bd2f3 100644
--- a/elf/dl-reloc-static-pie.c
+++ b/elf/dl-reloc-static-pie.c
@@ -17,6 +17,8 @@
    <https://www.gnu.org/licenses/>.  */
 
 #if ENABLE_STATIC_PIE
+/* Mark symbols hidden in static PIE for early self relocation to work.  */
+# pragma GCC visibility push(hidden)
 #include <unistd.h>
 #include <ldsodefs.h>
 #include "dynamic-link.h"
diff --git a/elf/dl-support.c b/elf/dl-support.c
index 2434c47..7abb65d 100644
--- a/elf/dl-support.c
+++ b/elf/dl-support.c
@@ -19,6 +19,12 @@
 /* This file defines some things that for the dynamic linker are defined in
    rtld.c and dl-sysdep.c in ways appropriate to bootstrap dynamic linking.  */
 
+#include <string.h>
+/* Mark symbols hidden in static PIE for early self relocation to work.
+   Note: string.h may have ifuncs which cannot be hidden on i686.  */
+#if BUILD_PIE_DEFAULT
+# pragma GCC visibility push(hidden)
+#endif
 #include <errno.h>
 #include <libintl.h>
 #include <stdlib.h>
diff --git a/elf/dl-tunables.c b/elf/dl-tunables.c
index e44476f..b1a50b8 100644
--- a/elf/dl-tunables.c
+++ b/elf/dl-tunables.c
@@ -18,6 +18,10 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
+/* Mark symbols hidden in static PIE for early self relocation to work.  */
+#if BUILD_PIE_DEFAULT
+# pragma GCC visibility push(hidden)
+#endif
 #include <startup.h>
 #include <stdint.h>
 #include <stdbool.h>
diff --git a/elf/enbl-secure.c b/elf/enbl-secure.c
index 5dcf649..9e47526 100644
--- a/elf/enbl-secure.c
+++ b/elf/enbl-secure.c
@@ -19,6 +19,10 @@
 /* This file is used in the static libc.  For the shared library,
    dl-sysdep.c defines and initializes __libc_enable_secure.  */
 
+/* Mark symbols hidden in static PIE for early self relocation to work.  */
+#if BUILD_PIE_DEFAULT
+# pragma GCC visibility push(hidden)
+#endif
 #include <startup.h>
 #include <libc-internal.h>
 
diff --git a/misc/sbrk.c b/misc/sbrk.c
index 99b3fb5..95800b3 100644
--- a/misc/sbrk.c
+++ b/misc/sbrk.c
@@ -15,6 +15,10 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
+/* Mark symbols hidden in static PIE for early self relocation to work.  */
+#if BUILD_PIE_DEFAULT
+# pragma GCC visibility push(hidden)
+#endif
 #include <errno.h>
 #include <libc-internal.h>
 #include <stdbool.h>
diff --git a/sysdeps/unix/sysv/linux/aarch64/libc-start.c b/sysdeps/unix/sysv/linux/aarch64/libc-start.c
index f816f04..e1604a6 100644
--- a/sysdeps/unix/sysv/linux/aarch64/libc-start.c
+++ b/sysdeps/unix/sysv/linux/aarch64/libc-start.c
@@ -17,6 +17,11 @@
    <https://www.gnu.org/licenses/>.  */
 
 #ifndef SHARED
+
+/* Mark symbols hidden in static PIE for early self relocation to work.  */
+# if BUILD_PIE_DEFAULT
+#  pragma GCC visibility push(hidden)
+# endif
 # include <ldsodefs.h>
 # include <cpu-features.c>
 
diff --git a/sysdeps/x86/libc-start.c b/sysdeps/x86/libc-start.c
index 4bbd7d5..d30aec2 100644
--- a/sysdeps/x86/libc-start.c
+++ b/sysdeps/x86/libc-start.c
@@ -16,6 +16,11 @@
    <https://www.gnu.org/licenses/>.  */
 
 #ifndef SHARED
+
+/* Mark symbols hidden in static PIE for early self relocation to work.  */
+# if BUILD_PIE_DEFAULT
+#  pragma GCC visibility push(hidden)
+# endif
 /* Define I386_USE_SYSENTER to support syscall during startup in static
    PIE.  */
 # include <startup.h>