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authorSzabolcs Nagy <szabolcs.nagy@arm.com>2021-01-06 11:31:04 +0000
committerSzabolcs Nagy <szabolcs.nagy@arm.com>2021-01-20 14:42:46 +0000
commitd7eb5cfd6953e9689c0306d808e234bd00741e6e (patch)
tree79de8c2f0521178cb8319b470ca02e64b328b6ef
parentb5dbaa167f4317c312e22fb761036d3570e6614a (diff)
downloadglibc-nsz/bug27072.tar.gz
Make libc symbols hidden in static PIEnsz/bug27072
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.
-rw-r--r--include/libc-symbols.h9
1 files 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")))