Re: [PATCH] make gcc -O1 in fs/reiserfs optional
From: Andrew Morton <hidden>
Date: 2005-10-13 23:31:33
Olaf Hering [off-list ref] wrote:
On Wed, Apr 27, Hans Reiser wrote:quoted
Olaf Hering wrote:quoted
Jeff, you added this EXTRA_CFLAGS= during 2.4 development, I think the broken compiler was gcc 3.2 on SLES8. Can we turn this -O1 into a .config option?quoted
Sounds reasonable.only compile with -O1 if the (very old) compiler is broken We use reiserfs alot in SLES9 on ppc64, and it was never seen with gcc33.
I dunno about this.
quoted hunk ↗ jump to hunk
Index: linux-2.6.12-rc3-olh/fs/reiserfs/Makefile ===================================================================--- linux-2.6.12-rc3-olh.orig/fs/reiserfs/Makefile +++ linux-2.6.12-rc3-olh/fs/reiserfs/Makefile@@ -21,13 +21,7 @@ ifeq ($(CONFIG_REISERFS_FS_POSIX_ACL),y) reiserfs-objs += xattr_acl.o endif -# gcc -O2 (the kernel default) is overaggressive on ppc32 when many inline -# functions are used. This causes the compiler to advance the stack -# pointer out of the available stack space, corrupting kernel space, -# and causing a panic. Since this behavior only affects ppc32, this ifeq -# will work around it. If any other architecture displays this behavior, -# add it here. -ifeq ($(CONFIG_PPC32),y) +ifeq ($(CONFIG_REISERFS_CC_REDUCE_OPTIMZE),y) EXTRA_CFLAGS := -O1 endifIndex: linux-2.6.12-rc3-olh/fs/Kconfig ===================================================================--- linux-2.6.12-rc3-olh.orig/fs/Kconfig +++ linux-2.6.12-rc3-olh/fs/Kconfig@@ -186,6 +186,18 @@ config REISERFS_FS If you like it, you can pay us to add new features to it that you need, buy a support contract, or pay us to port it to another OS. +config REISERFS_CC_REDUCE_OPTIMZE + bool "Reduce CC optimization level to workaround compiler bugs" + depends on PPC32 + default n + help + gcc -O2 (the kernel default) is overaggressive on ppc32 when many inline + functions are used. This causes the compiler to advance the stack + pointer out of the available stack space, corrupting kernel space, + and causing a panic. Since this behavior only affects ppc32, this ifeq + will work around it. If any other architecture displays this behavior, + add it here. +
Are you sure it's due to inline functions? I thought the problem was that certain versions of gcc did automatic inlining of non-inlined functions and we get excessive stack windup due to that. And iirc we put in global compiler options to defeat that behaviour. Andi would recall. Furthermore, we do have infrastructure for detecting the gcc version at build time. It would be better to use that for disabling `-O2', rather than a config option.