nixpkgs/pkgs/os-specific/linux/zfs/gcc-4.8.patch
Ricardo M. Correia d01242edb8 zfs: Fix minor filesystem corruption with gcc 4.8
It turns out that some of gcc 4.8's aggressive optimizations may
cause minor filesystem corruption in ZFS. To fix it, a patch was
cherry-picked from the upstream's git tree.

See: https://github.com/zfsonlinux/zfs/pull/2051
2014-03-04 12:58:11 +01:00

115 lines
4.5 KiB
Diff

commit 0f62f3f9abc4bfa0bcafee9bfa3d55e91dcb371d
Author: Brian Behlendorf <behlendorf1@llnl.gov>
Date: Tue Jan 14 09:39:13 2014 -0800
Disable GCCs aggressive loop optimization
GCC >+ 4.8's aggressive loop optimization breaks some of the iterators
over the dn_blkptr[] pseudo-array in dnode_phys. Since dn_blkptr[] is
defined as a single-element array, GCC believes an iterator can only
access index 0 and will unroll the loop into a single iteration.
One way to resolve the issue would be to cast the array to a pointer
and fix all the iterators that might break. The only loop where it
is known to cause a problem is this loop in dmu_objset_write_ready():
for (i = 0; i < dnp->dn_nblkptr; i++)
bp->blk_fill += dnp->dn_blkptr[i].blk_fill;
In the common case where dn_nblkptr is 3, the loop is only executed a
single time and "i" is equal to 1 following the loop.
The specific breakage caused by this problem is that the blk_fill of
root block pointers wouldn't be set properly when more than one blkptr
is in use (when no indrect blocks are needed).
The simple reproducing sequence is:
zpool create tank /tank.img
zdb -ddddd tank 0
Notice that "fill=31", however, there are two L0 indirect blocks with
"F=31" and "F=5". The fill count should be 36 rather than 31. This
problem causes an assert to be hit in a simple "zdb tank" when built
with --enable-debug.
However, this approach was not taken because we need to be absolutely
sure we catch all instances of this unwanted optimization. Therefore,
the build system has been updated to detect if GCC supports the
aggressive loop optimization. If it does the optimization will be
explicitly disabled using the -fno-aggressive-loop-optimization option.
Original-fix-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Tim Chase <tim@chase2k.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2010
Closes #2051
diff --git a/config/Rules.am b/config/Rules.am
index e3fa5b5..24f9426 100644
--- a/config/Rules.am
+++ b/config/Rules.am
@@ -1,8 +1,10 @@
DEFAULT_INCLUDES = -include ${top_builddir}/zfs_config.h
AM_LIBTOOLFLAGS = --silent
-AM_CFLAGS = -Wall -Wstrict-prototypes
-AM_CFLAGS += -fno-strict-aliasing ${NO_UNUSED_BUT_SET_VARIABLE} ${DEBUG_CFLAGS}
+AM_CFLAGS = ${DEBUG_CFLAGS} -Wall -Wstrict-prototypes
+AM_CFLAGS += ${NO_UNUSED_BUT_SET_VARIABLE}
+AM_CFLAGS += ${NO_AGGRESSIVE_LOOP_OPTIMIZATIONS}
+AM_CFLAGS += -fno-strict-aliasing
AM_CPPFLAGS = -D_GNU_SOURCE -D__EXTENSIONS__ -D_REENTRANT
AM_CPPFLAGS += -D_POSIX_PTHREAD_SEMANTICS -D_FILE_OFFSET_BITS=64
AM_CPPFLAGS += -D_LARGEFILE64_SOURCE -DTEXT_DOMAIN=\"zfs-linux-user\"
diff --git a/config/always-no-aggressive-loop-optimizations.m4 b/config/always-no-aggressive-loop-optimizations.m4
new file mode 100644
index 0000000..8f2115a
--- /dev/null
+++ b/config/always-no-aggressive-loop-optimizations.m4
@@ -0,0 +1,20 @@
+dnl #
+dnl # Check if gcc supports -fno-aggressive-loop-optimizations
+dnl #
+AC_DEFUN([ZFS_AC_CONFIG_ALWAYS_NO_AGGRESSIVE_LOOP_OPTIMIZATIONS], [
+ AC_MSG_CHECKING([for -fno-aggressive-loop-optimizations support])
+
+ saved_flags="$CFLAGS"
+ CFLAGS="$CFLAGS -fno-aggressive-loop-optimizations"
+
+ AC_RUN_IFELSE([AC_LANG_PROGRAM([], [])], [
+ NO_AGGRESSIVE_LOOP_OPTIMIZATIONS=-fno-aggressive-loop-optimizations
+ AC_MSG_RESULT([yes])
+ ], [
+ NO_AGGRESSIVE_LOOP_OPTIMIZATIONS=
+ AC_MSG_RESULT([no])
+ ])
+
+ CFLAGS="$saved_flags"
+ AC_SUBST([NO_AGGRESSIVE_LOOP_OPTIMIZATIONS])
+])
diff --git a/config/kernel.m4 b/config/kernel.m4
index cbf0ca3..62a9b42 100644
--- a/config/kernel.m4
+++ b/config/kernel.m4
@@ -104,6 +104,7 @@ AC_DEFUN([ZFS_AC_CONFIG_KERNEL], [
dnl # -Wall -fno-strict-aliasing -Wstrict-prototypes and other
dnl # compiler options are added by the kernel build system.
KERNELCPPFLAGS="$KERNELCPPFLAGS $NO_UNUSED_BUT_SET_VARIABLE"
+ KERNELCPPFLAGS="$KERNELCPPFLAGS $NO_AGGRESSIVE_LOOP_OPTIMIZATIONS"
KERNELCPPFLAGS="$KERNELCPPFLAGS -DHAVE_SPL -D_KERNEL"
KERNELCPPFLAGS="$KERNELCPPFLAGS -DTEXT_DOMAIN=\\\"zfs-linux-kernel\\\""
diff --git a/config/zfs-build.m4 b/config/zfs-build.m4
index 005185b..477b916 100644
--- a/config/zfs-build.m4
+++ b/config/zfs-build.m4
@@ -62,6 +62,7 @@ AC_DEFUN([ZFS_AC_DEBUG_DMU_TX], [
AC_DEFUN([ZFS_AC_CONFIG_ALWAYS], [
ZFS_AC_CONFIG_ALWAYS_NO_UNUSED_BUT_SET_VARIABLE
+ ZFS_AC_CONFIG_ALWAYS_NO_AGGRESSIVE_LOOP_OPTIMIZATIONS
])
AC_DEFUN([ZFS_AC_CONFIG], [