On 2014.07.26 at 12:56 -0700, Linus Torvalds wrote: > On Sat, Jul 26, 2014 at 12:35 PM, Markus Trippelsdorf > <mar...@trippelsdorf.de> wrote: > > > > But fortunately the workaround for the new inode.c bug is the same as > > for the original bug: -fno-var-tracking-assignments. > > > > It would make sense to enabled it unconditionally for all debug > > configurations for now. > > So how is code generation affected - if at all? Does the whole > "var-tracking-assignments" thing *only* matter for debug information?
Yes. It should only affect the quality of the debugging information. If code generation is affected it is a compiler bug. > Also, when was it introduced as an option? Can we just unconditionally > enable it, or do we need to be careful about gcc versions? Git blame says it was introduced: Wed Sep 2 02:42:21 2009. > I'd *like* a debug kernel to not differ significantly from a non-debug > kernel. Most sane kernel developers (where "sane" is "me" by > definition) do not tend to use debug kernels, because the debug > overhead is absolutely disgustingly enormous at build time. But if we > then have most users using distro kernels that had debug info enabled, > it would be sad if code generation differences are huge. > > So I'd prefer to just unconditionally add that > "-fno-var-tracking-assignments" to the build. > > I just tested it on one file (fs/dcache.c) and it made no difference > at all for my non-debug build. Is this expected? Yes. The option only affects -g builds. > Because if the only effect of "-fno-var-tracking-assignments" is > potentially slightly worse debug information for variables, I'll > enable it in a jiffy if it fixes this code generation bug. But I'd > like to get that confirmed. > > Finally, for CONFIG_DEBUG_INFO_REDUCED, we already use > "-fno-var-tracking". Is that a stronger version that also disables > "var-tracking-assignments"? Yes. So, the option should only be enabled for debugging builds. Something like the following should be sufficient: diff --git a/Makefile b/Makefile index 6b2774145d66..037b78d0f407 100644 --- a/Makefile +++ b/Makefile @@ -689,7 +689,7 @@ endif endif ifdef CONFIG_DEBUG_INFO -KBUILD_CFLAGS += -g +KBUILD_CFLAGS += -g -fno-var-tracking-assignments KBUILD_AFLAGS += -Wa,-gdwarf-2 endif -- Markus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
