This is the mail archive of the libc-alpha@sourceware.org mailing list for the glibc project.

Index Nav:	[Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav:	[Date Prev] [Date Next]	[Thread Prev] [Thread Next]
Other format:	[Raw text]

Re: [PATCH v3 2/9] Use gcc attribute ifunc in libc_ifunc macro instead of inline assembly due to false debuginfo.

From: Stefan Liebler <stli at linux dot vnet dot ibm dot com>
To: libc-alpha at sourceware dot org
Date: Tue, 30 Aug 2016 16:12:09 +0200
Subject: Re: [PATCH v3 2/9] Use gcc attribute ifunc in libc_ifunc macro instead of inline assembly due to false debuginfo.
Authentication-results: sourceware.org; auth=none
References: <1472047472-30307-1-git-send-email-stli@linux.vnet.ibm.com> <1472047472-30307-2-git-send-email-stli@linux.vnet.ibm.com> <fdf134f7-81b9-81a2-4447-f45427614640@linux.vnet.ibm.com>

On 08/29/2016 10:16 PM, Paul E. Murphy wrote:



On 08/24/2016 09:04 AM, Stefan Liebler wrote:


This way there is no trouble with the internal __GI_* symbols.
Glibc builds fine with this construct and the debuginfo is "correct".
For functions without a __GI_* symbol like memccpy this redirection is not needed.


Should memccpy read mempcpy?  Also, is the reason why you are able to remove the
libc_hidden_def usage later on in this patch?

Sorry. This comment means sysdeps/s390/multiarch/memccpy.c. There isalso a weak alias but no __GI_* symbol.


Regarding mempcpy in powerpc:
Before this patch there were two __GI_mempcpy symbols in powerpc-build:
readelf -s string/mempcpy.os | grep __GI_mempcpy
    16: 0000000000000000   156 IFUNC   WEAK   HIDDEN     7 __GI_mempcpy

readelf -s string/mempcpy-ppc64.os | grep __GI_mempcpy
    13: 0000000000000000    64 FUNC    GLOBAL DEFAULT    6 __GI_mempcpy

This only works as the IFUNC-one is weak. The resulting libc.so uses thenon-IFUNC-one:

readelf -s libc.so | grep _mempcpy
  4716: 00000000001d8580    64 FUNC    LOCAL  DEFAULT   27 __GI_mempcpy
  5360: 00000000001d8580    64 FUNC    LOCAL  DEFAULT   27 __mempcpy_ppc
...

With the redirection I can remove the libc_hidden_def (mempcpy) insysdeps/powerpc/powerpc64/multiarch/mempcpy.c andsysdeps/powerpc/powerpc32/power4/multiarch/mempcpy.c. Now it is obviousthat the libc_hidden_def insysdeps/powerpc/powerpc64/multiarch/mempcpy-ppc64.c andsysdeps/powerpc/powerpc32/power4/multiarch/mempcpy-ppc32.c is used.

--- a/sysdeps/powerpc/powerpc32/power4/fpu/multiarch/s_finite.c
+++ b/sysdeps/powerpc/powerpc32/power4/fpu/multiarch/s_finite.c
@@ -16,6 +16,9 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */

+#define __finite __redirect___finite
+#define __finitef __redirect___finitef
+#define __finitel __redirect___finitel

finitef and finitel don't seem to be needed here.

If I omit the the redirection of finitef and finitel the following erroroccurs (See my further comments below):

gcc ../sysdeps/powerpc/powerpc64/fpu/multiarch/s_finite.c -c ...
In file included from <command-line>:0:0:

../include/math.h:15:15: error: ‘__finitef’ undeclared here (not in afunction)

 hidden_proto (__finitef)
               ^

./../include/libc-symbols.h:409:27: note: in definition of macro‘__hidden_proto’extern thread __typeof (name) name __asm__ (__hidden_asmname(#internal)) \

                           ^
../include/math.h:15:1: note: in expansion of macro ‘hidden_proto’
 hidden_proto (__finitef)
 ^

../include/math.h:20:15: error: ‘__finitel’ undeclared here (not in afunction)

 hidden_proto (__finitel)
               ^

./../include/libc-symbols.h:409:27: note: in definition of macro‘__hidden_proto’extern thread __typeof (name) name __asm__ (__hidden_asmname(#internal)) \

                           ^
../include/math.h:20:1: note: in expansion of macro ‘hidden_proto’
 hidden_proto (__finitel)
 ^
In file included from ../sysdeps/powerpc/fpu/math_private.h:26:0,
                 from ../sysdeps/ieee754/ldbl-opt/math_ldbl_opt.h:40,

from../sysdeps/powerpc/powerpc64/fpu/multiarch/s_finite.c:23:../sysdeps/generic/math_private.h:325:12: error: ‘__finitel’ redeclaredas different kind of symbol

 extern int __finitel (long double);
            ^
In file included from <command-line>:0:0:
../include/math.h:20:15: note: previous declaration of ‘__finitel’ was here
 hidden_proto (__finitel)
               ^

./../include/libc-symbols.h:409:33: note: in definition of macro‘__hidden_proto’extern thread __typeof (name) name __asm__ (__hidden_asmname(#internal)) \

                                 ^
../include/math.h:20:1: note: in expansion of macro ‘hidden_proto’
 hidden_proto (__finitel)

Due to the mechanism in math.h (see below) the redirection of __finiteleads to also redirecting the definition of __finitef, __finitel as itis also used in those __MATHDECL_1 usages in math/bits/mathcalls.h butnot in include/math.h when using hidden_proto (__finite[fl]).

Thus I also have to redirect the float and long double versions.
This also applies to __isinf, __isnan.

include/math.h:
 3: #include <math/math.h>
15: hidden_proto (__finitef)
20: hidden_proto (__finitel)

math/math.h:
96: #define __MATHDECL_1(type, function,suffix, args) \
  extern type __MATH_PRECNAME(function,suffix) args __THROW
104, 125, 172: #include <bits/mathcalls.h>
(for float, double, long double math functions)

math/bits/mathcalls.h:

194:__MATHDECL_1 (int,__isinf,, (_Mdouble_ __value)) __attribute__((__const__));197: __MATHDECL_1 (int,__finite,, (_Mdouble_ __value)) __attribute__((__const__));236: __MATHDECL_1 (int,__isnan,, (_Mdouble_ __value)) __attribute__((__const__));

 #include <math.h>
 #include <math_ldbl_opt.h>
 #include <shlib-compat.h>
@@ -23,11 +26,14 @@

 extern __typeof (__finite) __finite_ppc32 attribute_hidden;
 extern __typeof (__finite) __finite_power7 attribute_hidden;
-
-libc_ifunc (__finite,
-	    (hwcap & PPC_FEATURE_ARCH_2_06)
-	    ? __finite_power7
-            : __finite_ppc32);
+#undef __finite
+#undef __finitef
+#undef __finitel

Likewise.

diff --git a/sysdeps/powerpc/powerpc32/power4/fpu/multiarch/s_isinf.c b/sysdeps/powerpc/powerpc32/power4/fpu/multiarch/s_isinf.c
index 506c111..fe6c912 100644
--- a/sysdeps/powerpc/powerpc32/power4/fpu/multiarch/s_isinf.c
+++ b/sysdeps/powerpc/powerpc32/power4/fpu/multiarch/s_isinf.c
@@ -16,6 +16,9 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */

+#define __isinf __redirect___isinf
+#define __isinff __redirect___isinff
+#define __isinfl __redirect___isinfl

Similarly, __isinff and __isinfl don't seem to need indirect.