Add patch from Josh Stone to restore var-tracking via Kconfig (rhbz 1126580)

This commit is contained in:
Josh Boyer 2014-12-16 12:13:21 -05:00
parent 2b541ad477
commit 401d0d95f4
3 changed files with 101 additions and 0 deletions

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@ -0,0 +1,92 @@
From: Josh Stone <jistone@redhat.com>
Date: Fri, 21 Nov 2014 10:40:00 -0800
Subject: [PATCH] Kbuild: Add an option to enable GCC VTA
MIME-Version: 1.0
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Due to recent codegen issues, gcc -fvar-tracking-assignments was
unconditionally disabled in commit 2062afb4f804a ("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: Frank Ch. Eigler <fche@redhat.com>
Cc: Jakub Jelinek <jakub@redhat.com>
Cc: Josh Boyer <jwboyer@fedoraproject.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Markus Trippelsdorf <markus@trippelsdorf.de>
Cc: Michel Dänzer <michel@daenzer.net>
Signed-off-by: Josh Stone <jistone@redhat.com>
---
Makefile | 4 ++++
lib/Kconfig.debug | 18 +++++++++++++++++-
2 files changed, 21 insertions(+), 1 deletion(-)
diff --git a/Makefile b/Makefile
index fd80c6e9bc23..4ba81e0dce46 100644
--- a/Makefile
+++ b/Makefile
@@ -704,7 +704,11 @@ KBUILD_CFLAGS += -fomit-frame-pointer
endif
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
ifdef CONFIG_DEBUG_INFO
ifdef CONFIG_DEBUG_INFO_SPLIT
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 4e35a5d767ed..27410417de1d 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -165,7 +165,23 @@ config DEBUG_INFO_DWARF4
Generate dwarf4 debug info. This requires recent versions
of gcc and gdb. It makes the debug information larger.
But it significantly improves the success of resolving
- variables in gdb on optimized code.
+ variables in gdb on optimized code. The gcc docs also
+ recommend enabling -fvar-tracking-assignments for maximum
+ benefit. (see DEBUG_INFO_VTA)
+
+config DEBUG_INFO_VTA
+ bool "Enable var-tracking-assignments for debuginfo"
+ depends on DEBUG_INFO
+ help
+ Enable gcc -fvar-tracking-assignments for improved debug
+ information on variable locations in optimized code. Per
+ gcc, DEBUG_INFO_DWARF4 is recommended for best use of VTA.
+
+ VTA has been implicated in codegen bugs (gcc PR61801,
+ PR61904), so this may deserve some caution. One can set
+ GCC_COMPARE_DEBUG=-fvar-tracking-assignments-toggle in the
+ environment to automatically compile everything both ways,
+ generating an error if anything differs.
config ENABLE_WARN_DEPRECATED
bool "Enable __deprecated logic"
--
2.1.0

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@ -4372,6 +4372,7 @@ CONFIG_FRAME_WARN=1024
CONFIG_MAGIC_SYSRQ=y CONFIG_MAGIC_SYSRQ=y
CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE=0x0 CONFIG_MAGIC_SYSRQ_DEFAULT_ENABLE=0x0
CONFIG_DEBUG_INFO=y CONFIG_DEBUG_INFO=y
CONFIG_DEBUG_INFO_VTA=y
# Revisit both of these options # Revisit both of these options
# CONFIG_DEBUG_INFO_SPLIT is not set # CONFIG_DEBUG_INFO_SPLIT is not set
# CONFIG_DEBUG_INFO_DWARF4 is not set # CONFIG_DEBUG_INFO_DWARF4 is not set

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@ -519,6 +519,9 @@ Patch530: silence-fbcon-logo.patch
Patch600: lib-cpumask-Make-CPUMASK_OFFSTACK-usable-without-deb.patch Patch600: lib-cpumask-Make-CPUMASK_OFFSTACK-usable-without-deb.patch
#rhbz 1126580
Patch601: Kbuild-Add-an-option-to-enable-GCC-VTA.patch
Patch800: crash-driver.patch Patch800: crash-driver.patch
# crypto/ # crypto/
@ -1278,6 +1281,8 @@ ApplyPatch input-silence-i8042-noise.patch
ApplyPatch silence-fbcon-logo.patch ApplyPatch silence-fbcon-logo.patch
# Changes to upstream defaults. # Changes to upstream defaults.
#rhbz 1126580
ApplyPatch Kbuild-Add-an-option-to-enable-GCC-VTA.patch
# /dev/crash driver. # /dev/crash driver.
ApplyPatch crash-driver.patch ApplyPatch crash-driver.patch
@ -2243,6 +2248,9 @@ fi
# ||----w | # ||----w |
# || || # || ||
%changelog %changelog
* Tue Dec 16 2014 Josh Boyer <jwboyer@fedoraproject.org>
- Add patch from Josh Stone to restore var-tracking via Kconfig (rhbz 1126580)
* Mon Dec 15 2014 Josh Boyer <jwboyer@fedoraproject.org> * Mon Dec 15 2014 Josh Boyer <jwboyer@fedoraproject.org>
- Fix ppc64 boot with smt-enabled=off (rhbz 1173806) - Fix ppc64 boot with smt-enabled=off (rhbz 1173806)
- CVE-2014-8133 x86: espfix(64) bypass via set_thread_area and CLONE_SETTLS (rhbz 1172797 1174374) - CVE-2014-8133 x86: espfix(64) bypass via set_thread_area and CLONE_SETTLS (rhbz 1172797 1174374)