From: Szabolcs Nagy <szabolcs.nagy@arm.com>
To: libc-alpha@sourceware.org
Subject: [PATCH v2 2/4] Make libc symbols hidden in static PIE
Date: Fri, 8 Jan 2021 16:20:08 +0000 [thread overview]
Message-ID: <56297d0f9c00bd27901dc41ef20d749cf564def7.1610121077.git.szabolcs.nagy@arm.com> (raw)
In-Reply-To: <cover.1610121077.git.szabolcs.nagy@arm.com>
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 --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")))
--
2.17.1
next prev parent reply other threads:[~2021-01-08 16:20 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-08 16:19 [PATCH v2 0/4] fix ifunc with static pie [BZ #27072] Szabolcs Nagy
2021-01-08 16:19 ` [PATCH v2 1/4] configure: Require PI_STATIC_AND_HIDDEN for static pie Szabolcs Nagy
2021-01-08 16:20 ` Szabolcs Nagy [this message]
2021-01-08 16:20 ` [PATCH v2 3/4] elf: Avoid RELATIVE relocs in __tunables_init Szabolcs Nagy
2021-01-08 17:59 ` Adhemerval Zanella
2021-01-08 18:22 ` Siddhesh Poyarekar
2021-01-08 18:25 ` Adhemerval Zanella
2021-01-11 10:56 ` Szabolcs Nagy
2021-01-11 12:13 ` Adhemerval Zanella
2021-01-08 16:20 ` [PATCH v2 4/4] csu: Move static pie self relocation later [BZ #27072] Szabolcs Nagy
2021-01-08 17:04 ` [PATCH v2 0/4] fix ifunc with static pie " H.J. Lu
2021-01-11 10:50 ` Szabolcs Nagy
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