On Thu, Apr 23, 2015 at 5:25 PM, Frank Ch. Eigler <[email protected]> wrote: > From: Josh Stone <[email protected]> > > Due to isolated gcc codegen issues, gcc -fvar-tracking-assignments > was unconditionally disabled in commit 2062afb4f804 ("Fix gcc-4.9.0 > miscompilation of load_balance() in scheduler"). > > However, this reduces the debuginfo coverage for variable locations, > especially in inline functions. VTA is certainly not perfect either > in those cases, but it is much better than without. With compiler > versions that have fixed the codegen bugs, we would prefer to have the > better details for SystemTap, and surely other debuginfo consumers > like perf will benefit as well. > > This patch simply makes CONFIG_DEBUG_INFO_VTA an option. I considered > Frank and Linus's discussion of a cc-option-like -fcompare-debug test, > but I'm convinced that a narrow test of an arch-specific codegen issue > is not really useful. GCC has their own regression tests for this, so > I'd suggest GCC_COMPARE_DEBUG=-fvar-tracking-assignments-toggle is more > useful for kernel developers to test confidence. > > In fact, I ran into a couple more issues when testing for this patch[1], > although neither of those had any codegen impact. > [1] https://bugzilla.redhat.com/show_bug.cgi?id=1140872 > > With gcc-4.9.2-1.fc22, I can now build v3.18-rc5 with Fedora's i686 and > x86_64 configs, and this is completely clean with GCC_COMPARE_DEBUG. > > Cc: Jakub Jelinek <[email protected]> > Cc: Josh Boyer <[email protected]> > Cc: Greg Kroah-Hartman <[email protected]> > Cc: Linus Torvalds <[email protected]> > Cc: Andrew Morton <[email protected]> > Cc: Markus Trippelsdorf <[email protected]> > Cc: Michel Dänzer <[email protected]> > Signed-off-by: Josh Stone <[email protected]> > Signed-off-by: Frank Ch. Eigler <[email protected]>
Frank, did you rebase this against some newer tree or something? Curious why you sent it again. > Makefile | 8 ++++++-- > lib/Kconfig.debug | 21 ++++++++++++++++++++- > 2 files changed, 26 insertions(+), 3 deletions(-) > > diff --git a/Makefile b/Makefile > index 6cc5b2434224..c8e1fcfdb41a 100644 > --- a/Makefile > +++ b/Makefile > @@ -704,8 +704,6 @@ KBUILD_CFLAGS += -fomit-frame-pointer > endif > endif > > -KBUILD_CFLAGS += $(call cc-option, -fno-var-tracking-assignments) > - > ifdef CONFIG_DEBUG_INFO > ifdef CONFIG_DEBUG_INFO_SPLIT > KBUILD_CFLAGS += $(call cc-option, -gsplit-dwarf, -g) > @@ -718,6 +716,12 @@ ifdef CONFIG_DEBUG_INFO_DWARF4 > KBUILD_CFLAGS += $(call cc-option, -gdwarf-4,) > endif > > +ifdef CONFIG_DEBUG_INFO_VTA > +KBUILD_CFLAGS += $(call cc-option, -fvar-tracking-assignments) > +else > +KBUILD_CFLAGS += $(call cc-option, -fno-var-tracking-assignments) > +endif > + Is there a reason you moved this hunk under the DWARF4 options instead of modifying it in-place like the original patch did? josh -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
