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Enable hidden visibility in libc.a compiled with PIE

Message ID CAMe9rOqpH+xyemoffg7XCcdBA2qPjCLp70_S91T5GmEpbp6nvA@mail.gmail.com
State New, archived
Headers show

Commit Message

H.J. Lu Aug. 21, 2017, 5:33 p.m. UTC
On Mon, Aug 21, 2017 at 9:50 AM, Szabolcs Nagy <szabolcs.nagy@arm.com> wrote:
> On 21/08/17 17:44, H.J. Lu wrote:
>> On Mon, Aug 21, 2017 at 9:31 AM, Szabolcs Nagy <szabolcs.nagy@arm.com> wrote:
>>> On 08/08/17 17:40, H.J. Lu wrote:
>>>> When building libc.a with PIE, enable hidden visibility to allow direct
>>>> access to definitions within libc.a without using GOT.
>>> ...
>>>> -#if defined SHARED || defined LIBC_NONSHARED
>>>> +#if defined SHARED || defined LIBC_NONSHARED \
>>>> +  || (BUILD_PIE_DEFAULT && IS_IN (libc))
>>>>  # define attribute_hidden __attribute__ ((visibility ("hidden")))
>>>
>>> btw what happens if this is enabled for non-pie libc.a ?
>>
>> It makes those symbols in libc.a hidden.
>>
>>> i'd expect that to work too (it prevents some symbol
>>> interpositions?)
>>>
>>
>> You can't interpose any symbols in libc.a, PIE or non-PIE.
>> What my patch does is to avoid GOT/PLT in PIE libc.a when
>> accessing them within libc.a.
>>
>
> yes, but my point is that the ifdef can be simplified
> if it's valid for the non-pie case too.

Here is the patch.   Tested with PIE and non-PIE libc.a.

Any comments?
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Patch

From d301c3c02e70ee9ff50d173da7d4d9626767bc4c Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Mon, 21 Aug 2017 10:27:57 -0700
Subject: [PATCH] Always hide symbols referenced internally within libc.a

Since none of internal symbols within libc.a, PIE or non-PIE, can be
interposed, we can always hide symbols referenced internally within
libc.a.

	* include/libc-symbols.h (attribute_hidden): Remove
	BUILD_PIE_DEFAULT check.
---
 include/libc-symbols.h | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/include/libc-symbols.h b/include/libc-symbols.h
index fe3571af52..d11844b97d 100644
--- a/include/libc-symbols.h
+++ b/include/libc-symbols.h
@@ -363,8 +363,7 @@  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 || IS_IN (libc)
 # define attribute_hidden __attribute__ ((visibility ("hidden")))
 #else
 # define attribute_hidden
-- 
2.13.5