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Avoid linker bug on Microblaze (was Re: Default build-many-glibcs.py to GCC 7 branch [committed])
- From: Zack Weinberg <zackw at panix dot com>
- To: Joseph Myers <joseph at codesourcery dot com>
- Cc: GNU C Library <libc-alpha at sourceware dot org>
- Date: Tue, 30 May 2017 21:25:24 -0400
- Subject: Avoid linker bug on Microblaze (was Re: Default build-many-glibcs.py to GCC 7 branch [committed])
- Authentication-results: sourceware.org; auth=none
- References: <alpine.DEB.2.20.1704261527200.24779@digraph.polyomino.org.uk> <CAKCAbMgS_9LURjc_GYQLNciWpt7Ljx=V97txeiF3ioWY9KHV1g@mail.gmail.com> <alpine.DEB.2.20.1705101304060.3001@digraph.polyomino.org.uk>
On 05/10/2017 09:16 AM, Joseph Myers wrote:
> That said,
> <https://lists.yoctoproject.org/pipermail/meta-xilinx/2016-November/002258.html>
> seems to have a plausible explanation of the problem (alias to undefined
> __libc_vfork, apparently triggering a linker bug). I'd prefer making
> MicroBlaze follow the same symbol handling as other architectures (so
> defining __libc_vfork and then defining other symbols as aliases to it)
> over the approach in that patch of a MicroBlaze-specific pt-vfork.S.
Indeed, this fixes the problem. Is this roughly what you had in mind?
I'm probably gonna go ahead and check it in if I don't hear objections
in, like, 24 hours or so.
zw
--
[PATCH] Avoid tickling a linker bug from microblaze pt-vfork.S.
libpthread used to have its own vfork implementation that differed
from libc's only in having a pointless micro-optimization. There is
no longer any use to having a separate copy in libpthread, but the
historical ABI requires it. microblaze was trying to be slightly
too clever about how it did this, and tickled a linker bug. The
linker bug should get fixed eventually, but there's no reason for
us to keep tickling it in the meantime.
This doesn't reuse the generic pt-vfork.c because microblaze doesn't
have IFUNC support yet, and it doesn't reuse aarch64/pt-vfork.c
because that fails to generate a tailcall (with GCC 7.1.1).
* sysdeps/unix/sysv/linux/microblaze/pt-vfork.S: Don't include
alpha/pt-vfork.S. Provide own complete compat stub for vfork
and __vfork.
* sysdeps/unix/sysv/linux/microblaze/vfork.S: Add __libc_vfork
alias.
* sysdeps/unix/sysv/linux/microblaze/localplt.data:
libpthread.so no longer references __errno_location.
---
sysdeps/unix/sysv/linux/microblaze/localplt.data | 1 -
sysdeps/unix/sysv/linux/microblaze/pt-vfork.S | 50
+++++++++++++++++++++++-
sysdeps/unix/sysv/linux/microblaze/vfork.S | 1 +
3 files changed, 50 insertions(+), 2 deletions(-)
diff --git a/sysdeps/unix/sysv/linux/microblaze/localplt.data
b/sysdeps/unix/sysv/linux/microblaze/localplt.data
index a61b94dfb8..ca476bedd8 100644
--- a/sysdeps/unix/sysv/linux/microblaze/localplt.data
+++ b/sysdeps/unix/sysv/linux/microblaze/localplt.data
@@ -5,7 +5,6 @@ libc.so: malloc
libc.so: memalign
libc.so: realloc
libm.so: matherr
-libpthread.so: __errno_location
# The dynamic loader needs __tls_get_addr for TLS.
ld.so: __tls_get_addr ?
# The main malloc is interposed into the dynamic linker, for
diff --git a/sysdeps/unix/sysv/linux/microblaze/pt-vfork.S
b/sysdeps/unix/sysv/linux/microblaze/pt-vfork.S
index 65cc3823ac..f201f0429f 100644
--- a/sysdeps/unix/sysv/linux/microblaze/pt-vfork.S
+++ b/sysdeps/unix/sysv/linux/microblaze/pt-vfork.S
@@ -1 +1,49 @@
-#include <sysdeps/unix/sysv/linux/alpha/pt-vfork.S>
+/* vfork ABI-compatibility entry points for libpthread.
+ Copyright (C) 2014-2017 Free Software Foundation, Inc.
+ This file is part of the GNU C Library.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library is distributed in the hope that it will be useful,
+ but WITHOUT ANY WARRANTY; without even the implied warranty of
+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#include <sysdep.h>
+#include <shlib-compat.h>
+
+/* libpthread used to have its own vfork implementation that differed
+ from libc's only in having a pointless micro-optimization. There
+ is no longer any use to having a separate copy in libpthread, but
+ the historical ABI requires it. For static linking, there is no
+ need to provide anything here--the libc version will be linked in.
+ For shared library ABI compatibility, there must be __vfork and
+ vfork symbols in libpthread.so.
+
+ As of GCC 7, microblaze can *not* rely on the compiler to generate
+ a tail call from this vfork to __libc_vfork. */
+
+#if (SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_20) \
+ || SHLIB_COMPAT (libpthread, GLIBC_2_1_2, GLIBC_2_20))
+
+ENTRY (vfork_compat)
+ bri __libc_vfork
+END (vfork_compat)
+
+#endif
+
+#if SHLIB_COMPAT (libpthread, GLIBC_2_0, GLIBC_2_20)
+compat_symbol (libpthread, vfork_compat, vfork, GLIBC_2_0)
+#endif
+
+#if SHLIB_COMPAT (libpthread, GLIBC_2_1_2, GLIBC_2_20)
+strong_alias (vfork_compat, vfork_compat2)
+compat_symbol (libpthread, vfork_compat2, __vfork, GLIBC_2_1_2)
+#endif
diff --git a/sysdeps/unix/sysv/linux/microblaze/vfork.S
b/sysdeps/unix/sysv/linux/microblaze/vfork.S
index 1ad86229a9..f1e4508d20 100644
--- a/sysdeps/unix/sysv/linux/microblaze/vfork.S
+++ b/sysdeps/unix/sysv/linux/microblaze/vfork.S
@@ -43,3 +43,4 @@ PSEUDO_END (__vfork)
libc_hidden_def (__vfork)
weak_alias (__vfork, vfork)
+strong_alias (__vfork, __libc_vfork)
--
2.11.0