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Re: [PATCH] Use libc_hidden_proto / _def for hidden wchar ifunc symbols.
On 11/13/2017 06:30 PM, H.J. Lu wrote:
On Mon, Nov 13, 2017 at 9:11 AM, Stefan Liebler <stli@linux.vnet.ibm.com> wrote:
On 11/13/2017 02:58 PM, H.J. Lu wrote:
On Mon, Nov 13, 2017 at 3:55 AM, Florian Weimer <fweimer@redhat.com>
wrote:
On 11/13/2017 11:16 AM, Stefan Liebler wrote:
This patch adds the libc_hidden_proto / libc_hidden_def construct.
Then the __GI_* symbols are the default-ifunc-variants which can be
called
without PLT.
attribute_hidden and *_hidden_{proto,def} conflict on some architectures.
You need to remove attribute_hidden as part of this change.
That is true. On i686, a hidden IFUNC function inside libc.so must be
compiled
with -fPIC via PLT since EBX must be loaded with GOT first. This
isn't an issue
for x86-64 since PLT uses PC-relative addressing. In this case, we
should remove
hidden attribute, instead of using __GI_* symbols, if we sill want to use
IFUNC
inside libc.so.
For the moment, I propose to remove the attribute_hidden in order to fix
those internal IFUNC calls.
Is the attached patch okay to commit?
On s390/s390x, just removing attribute_hidden in wchar.h is fine, too. Then
r12 will be setup with the GOT-pointer and IFUNC will be used inside
libc.so.
What was your original intention? Getting rid of "PLT" or "PLT and IFUNC"
for calls inside libc.so?
The original intention is to remove PLT. But it doesn't work for targets which
need to set up a special register for PLT which is required by IFUNC.
Now I have question, is there a way to apply attribute_hidden to a
function
depending on architecture? For example, we remove attribute_hidden
from __wcsnlen, __wcscat, __wcsncpy, __wcpncpy, __wcschrnul in headers
under include/. For x86, we mark them hidden in a header file under
sysdeps/x86?
I don't know if duplicating the wchar.h file is such a good idea.
Can we add
#include <wcharP.h>
to include/wchar.h and add a dummy sysdeps/generic/wcharP.h? Then
I can add sysdeps/x86_64/wcharP.h to hide __wcsnlen, __wcscat, __wcsncpy,
_wcpncpy, __wcschrnul
@H.J. Lu: Can you propose a separate patch for architecture dependent
wcharP.h files?
Bye.
Stefan
commit 70c17e8f6a07236aaa37e1aab67703d3bc1e09a2
Author: Stefan Liebler <stli@linux.vnet.ibm.com>
Date: Mon Nov 20 12:26:24 2017 +0100
Remove attribute_hidden for wchar ifunc symbols.
On s390 (31bit) various debug/tst-*chk* testcases are failing as the tests
are ending with a segmentation fault.
One test is e.g. calling wcsnrtombs in debug/tst-chk1.c:1549.
The function wcsnrtombs itself calls __wcsnlen. This function is called via
PLT! The PLT-stub itself loads the address from GOT (r12 is assumed to be
the GOT-pointer). In this case the loaded address is zero and the following
branch leads to the segmentation fault.
Due to the attribute_hidden in commit 44af8a32c341672b5160fdc2839767e9a837ad26
"Mark internal wchar functions with attribute_hidden [BZ #18822]"
for e.g. the __wcsnlen function, r12 is not loaded with the GOT-pointer
in wcsnrtombs.
On s390x (64bit), this __wcsnlen call is also using the PLT-stub. But it is
not failing as the GOT-pointer is setup with larl-instruction by the PLT-stub
itself.
Note: On s390x/s390, __wcsnlen is an IFUNC symbol.
On x86_64, __wcsnlen is also an IFUNC symbol and is called via PLT, too.
Further IFUNC symbols on s390 which were marked as hidden by the mentioned
commit are: __wcscat, __wcsncpy, __wcpncpy, __wcschrnul.
This patch removes the attribute_hidden in wchar.h.
Then the compiler setups e.g. r12 on s390 in order to call __wcsnlen via PLT.
ChangeLog:
* include/wchar.h (__wcsnlen, __wcscat, __wcsncpy, __wcpncpy,
__wcschrnul): Remove attribute_hidden.
diff --git a/include/wchar.h b/include/wchar.h
index 24b2eaa..1db0ac8 100644
--- a/include/wchar.h
+++ b/include/wchar.h
@@ -152,9 +152,8 @@ extern int __wcsncasecmp (const wchar_t *__s1, const wchar_t *__s2,
__attribute_pure__;
extern size_t __wcslen (const wchar_t *__s) __attribute_pure__;
extern size_t __wcsnlen (const wchar_t *__s, size_t __maxlen)
- attribute_hidden __attribute_pure__;
-extern wchar_t *__wcscat (wchar_t *dest, const wchar_t *src)
- attribute_hidden;
+ __attribute_pure__;
+extern wchar_t *__wcscat (wchar_t *dest, const wchar_t *src);
extern wint_t __btowc (int __c) attribute_hidden;
extern int __mbsinit (const __mbstate_t *__ps);
extern size_t __mbrtowc (wchar_t *__restrict __pwc,
@@ -182,11 +181,10 @@ extern size_t __wcsnrtombs (char *__restrict __dst,
__mbstate_t *__restrict __ps)
attribute_hidden;
extern wchar_t *__wcsncpy (wchar_t *__restrict __dest,
- const wchar_t *__restrict __src, size_t __n)
- attribute_hidden;
+ const wchar_t *__restrict __src, size_t __n);
extern wchar_t *__wcpcpy (wchar_t *__dest, const wchar_t *__src);
extern wchar_t *__wcpncpy (wchar_t *__dest, const wchar_t *__src,
- size_t __n) attribute_hidden;
+ size_t __n);
extern wchar_t *__wmemcpy (wchar_t *__s1, const wchar_t *s2,
size_t __n) attribute_hidden;
extern wchar_t *__wmempcpy (wchar_t *__restrict __s1,
@@ -195,7 +193,7 @@ extern wchar_t *__wmempcpy (wchar_t *__restrict __s1,
extern wchar_t *__wmemmove (wchar_t *__s1, const wchar_t *__s2,
size_t __n) attribute_hidden;
extern wchar_t *__wcschrnul (const wchar_t *__s, wchar_t __wc)
- attribute_hidden __attribute_pure__;
+ __attribute_pure__;
extern wchar_t *__wmemset_chk (wchar_t *__s, wchar_t __c, size_t __n,
size_t __ns) __THROW;