Add hidden visibility to internal function prototypes
Commit Message
On Thu, Aug 17, 2017 at 5:40 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Thu, Aug 17, 2017 at 5:34 AM, Florian Weimer <fweimer@redhat.com> wrote:
>> On 08/17/2017 02:22 PM, H.J. Lu wrote:
>>> Add hidden visibility to internal function prototypes to allow direct
>>> access to internal functions within libc.a without using GOT when the
>>> compiler defaults to -fPIE.
>>>
>>> Size comparison of elf/ldconfig when the compiler defaults to -fPIE:
>>
>> This is for static linking, right?
>>
>> Is there a reason to restrict this to PIE builds? Why not use hidden
>> visibility unconditionally?
>>
>
> Yes, there is only used for static PIE build and we can replace
> BUILD_PIE_DEFAULT with !defined SHARED. But it makes
> no difference for non-PIE static build.
>
Here is the updated patch to add hidden visibility to internal function
prototypes used within libc.a.
Tested on x86-64 and i686 with and without GCC defaulting to PIE.
OK for master?
Comments
On Thu, Aug 17, 2017 at 11:25 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Thu, Aug 17, 2017 at 5:40 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> On Thu, Aug 17, 2017 at 5:34 AM, Florian Weimer <fweimer@redhat.com> wrote:
>>> On 08/17/2017 02:22 PM, H.J. Lu wrote:
>>>> Add hidden visibility to internal function prototypes to allow direct
>>>> access to internal functions within libc.a without using GOT when the
>>>> compiler defaults to -fPIE.
>>>>
>>>> Size comparison of elf/ldconfig when the compiler defaults to -fPIE:
>>>
>>> This is for static linking, right?
>>>
>>> Is there a reason to restrict this to PIE builds? Why not use hidden
>>> visibility unconditionally?
>>>
>>
>> Yes, there is only used for static PIE build and we can replace
>> BUILD_PIE_DEFAULT with !defined SHARED. But it makes
>> no difference for non-PIE static build.
>>
>
> Here is the updated patch to add hidden visibility to internal function
> prototypes used within libc.a.
>
> Tested on x86-64 and i686 with and without GCC defaulting to PIE.
>
> OK for master?
>
I will check it in tomorrow.
From 236f3b88f74d408d3ab925809da3bd6d8a995730 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Sun, 13 Aug 2017 07:37:34 -0700
Subject: [PATCH] Add hidden visibility to internal function prototypes
Add hidden visibility to internal function prototypes to allow direct
access to internal functions within libc.a without using GOT when the
compiler defaults to -fPIE.
Size comparison of elf/ldconfig when the compiler defaults to -fPIE:
On x86-64:
text data bss dec hex
Before: 619646 20132 5488 645266 9d892
After : 619502 20132 5488 645122 9d802
On i686:
text data bss dec hex
Before: 550333 10748 3060 564141 89bad
After : 546453 10732 3060 560245 88c75
* include/libc-symbols.h (__hidden_proto_hiddenattr): New for
building libc.a.
(hidden_proto): Likewise.
(hidden_tls_proto): Likewise.
(__hidden_proto): Likewise.
---
include/libc-symbols.h | 16 ++++++++++++++--
1 file changed, 14 insertions(+), 2 deletions(-)
@@ -513,8 +513,20 @@ for linking")
# endif
#else
# ifndef __ASSEMBLER__
-# define hidden_proto(name, attrs...)
-# define hidden_tls_proto(name, attrs...)
+# if !defined SHARED && IS_IN (libc) && !defined LIBC_NONSHARED \
+ && !defined NO_HIDDEN
+# define __hidden_proto_hiddenattr(attrs...) \
+ __attribute__ ((visibility ("hidden"), ##attrs))
+# define hidden_proto(name, attrs...) \
+ __hidden_proto (name, , name, ##attrs)
+# define hidden_tls_proto(name, attrs...) \
+ __hidden_proto (name, __thread, name, ##attrs)
+# define __hidden_proto(name, thread, internal, attrs...) \
+ extern thread __typeof (name) name __hidden_proto_hiddenattr (attrs);
+# else
+# define hidden_proto(name, attrs...)
+# define hidden_tls_proto(name, attrs...)
+# endif
# else
# define HIDDEN_JUMPTARGET(name) JUMPTARGET(name)
# endif /* Not __ASSEMBLER__ */
--
2.13.5