[OE-core] [PATCH 7/7] linux-yocto_4.1.bb: Fix build with gcc7
Khem Raj
raj.khem at gmail.com
Sat May 13 16:10:58 UTC 2017
On Sat, May 13, 2017 at 8:45 AM, Bruce Ashfield
<bruce.ashfield at gmail.com> wrote:
> I already have this queued, I'm just not sending any kernel pull requests
> while
> the release is finalizing.
its already done yesterday :) so you are free to send
>
> So please, do not queue or merge this change.
>
sure
> Bruce
>
> On Fri, May 12, 2017 at 10:59 PM, Khem Raj <raj.khem at gmail.com> wrote:
>>
>> Signed-off-by: Khem Raj <raj.khem at gmail.com>
>> ---
>> ...ve-up-on-gcc-ilog2-constant-optimizations.patch | 134
>> +++++++++++++++++++++
>> meta/recipes-kernel/linux/linux-yocto_4.1.bb | 2 +
>> 2 files changed, 136 insertions(+)
>> create mode 100644
>> meta/recipes-kernel/linux/linux-yocto/0001-give-up-on-gcc-ilog2-constant-optimizations.patch
>>
>> diff --git
>> a/meta/recipes-kernel/linux/linux-yocto/0001-give-up-on-gcc-ilog2-constant-optimizations.patch
>> b/meta/recipes-kernel/linux/linux-yocto/0001-give-up-on-gcc-ilog2-constant-optimizations.patch
>> new file mode 100644
>> index 0000000000..35c4484f20
>> --- /dev/null
>> +++
>> b/meta/recipes-kernel/linux/linux-yocto/0001-give-up-on-gcc-ilog2-constant-optimizations.patch
>> @@ -0,0 +1,134 @@
>> +From 273bf720b7acb5f808337fe57c5f400422a30051 Mon Sep 17 00:00:00 2001
>> +From: Linus Torvalds <torvalds at linux-foundation.org>
>> +Date: Thu, 2 Mar 2017 12:17:22 -0800
>> +Subject: [PATCH] give up on gcc ilog2() constant optimizations
>> +
>> +commit 474c90156c8dcc2fa815e6716cc9394d7930cb9c upstream.
>> +
>> +gcc-7 has an "optimization" pass that completely screws up, and
>> +generates the code expansion for the (impossible) case of calling
>> +ilog2() with a zero constant, even when the code gcc compiles does not
>> +actually have a zero constant.
>> +
>> +And we try to generate a compile-time error for anybody doing ilog2() on
>> +a constant where that doesn't make sense (be it zero or negative). So
>> +now gcc7 will fail the build due to our sanity checking, because it
>> +created that constant-zero case that didn't actually exist in the source
>> +code.
>> +
>> +There's a whole long discussion on the kernel mailing about how to work
>> +around this gcc bug. The gcc people themselevs have discussed their
>> +"feature" in
>> +
>> + https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72785
>> +
>> +but it's all water under the bridge, because while it looked at one
>> +point like it would be solved by the time gcc7 was released, that was
>> +not to be.
>> +
>> +So now we have to deal with this compiler braindamage.
>> +
>> +And the only simple approach seems to be to just delete the code that
>> +tries to warn about bad uses of ilog2().
>> +
>> +So now "ilog2()" will just return 0 not just for the value 1, but for
>> +any non-positive value too.
>> +
>> +It's not like I can recall anybody having ever actually tried to use
>> +this function on any invalid value, but maybe the sanity check just
>> +meant that such code never made it out in public.
>> +
>> +Reported-by: Laura Abbott <labbott at redhat.com>
>> +Cc: John Stultz <john.stultz at linaro.org>,
>> +Cc: Thomas Gleixner <tglx at linutronix.de>
>> +Cc: Ard Biesheuvel <ard.biesheuvel at linaro.org>
>> +Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
>> +Cc: Jiri Slaby <jslaby at suse.cz>
>> +Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
>> +Signed-off-by: Khem Raj <raj.khem at gmail.com>
>> +---
>> +Upstream-Status: Backport
>> +
>> + include/linux/log2.h | 13 ++-----------
>> + tools/include/linux/log2.h | 13 ++-----------
>> + 2 files changed, 4 insertions(+), 22 deletions(-)
>> +
>> +diff --git a/include/linux/log2.h b/include/linux/log2.h
>> +index fd7ff3d91e6a..f38fae23bdac 100644
>> +--- a/include/linux/log2.h
>> ++++ b/include/linux/log2.h
>> +@@ -16,12 +16,6 @@
>> + #include <linux/bitops.h>
>> +
>> + /*
>> +- * deal with unrepresentable constant logarithms
>> +- */
>> +-extern __attribute__((const, noreturn))
>> +-int ____ilog2_NaN(void);
>> +-
>> +-/*
>> + * non-constant log of base 2 calculators
>> + * - the arch may override these in asm/bitops.h if they can be
>> implemented
>> + * more efficiently than using fls() and fls64()
>> +@@ -85,7 +79,7 @@ unsigned long __rounddown_pow_of_two(unsigned long n)
>> + #define ilog2(n) \
>> + ( \
>> + __builtin_constant_p(n) ? ( \
>> +- (n) < 1 ? ____ilog2_NaN() : \
>> ++ (n) < 2 ? 0 : \
>> + (n) & (1ULL << 63) ? 63 : \
>> + (n) & (1ULL << 62) ? 62 : \
>> + (n) & (1ULL << 61) ? 61 : \
>> +@@ -148,10 +142,7 @@ unsigned long __rounddown_pow_of_two(unsigned long
>> n)
>> + (n) & (1ULL << 4) ? 4 : \
>> + (n) & (1ULL << 3) ? 3 : \
>> + (n) & (1ULL << 2) ? 2 : \
>> +- (n) & (1ULL << 1) ? 1 : \
>> +- (n) & (1ULL << 0) ? 0 : \
>> +- ____ilog2_NaN() \
>> +- ) : \
>> ++ 1 ) : \
>> + (sizeof(n) <= 4) ? \
>> + __ilog2_u32(n) : \
>> + __ilog2_u64(n) \
>> +diff --git a/tools/include/linux/log2.h b/tools/include/linux/log2.h
>> +index 41446668ccce..d5677d39c1e4 100644
>> +--- a/tools/include/linux/log2.h
>> ++++ b/tools/include/linux/log2.h
>> +@@ -13,12 +13,6 @@
>> + #define _TOOLS_LINUX_LOG2_H
>> +
>> + /*
>> +- * deal with unrepresentable constant logarithms
>> +- */
>> +-extern __attribute__((const, noreturn))
>> +-int ____ilog2_NaN(void);
>> +-
>> +-/*
>> + * non-constant log of base 2 calculators
>> + * - the arch may override these in asm/bitops.h if they can be
>> implemented
>> + * more efficiently than using fls() and fls64()
>> +@@ -78,7 +72,7 @@ unsigned long __rounddown_pow_of_two(unsigned long n)
>> + #define ilog2(n) \
>> + ( \
>> + __builtin_constant_p(n) ? ( \
>> +- (n) < 1 ? ____ilog2_NaN() : \
>> ++ (n) < 2 ? 0 : \
>> + (n) & (1ULL << 63) ? 63 : \
>> + (n) & (1ULL << 62) ? 62 : \
>> + (n) & (1ULL << 61) ? 61 : \
>> +@@ -141,10 +135,7 @@ unsigned long __rounddown_pow_of_two(unsigned long
>> n)
>> + (n) & (1ULL << 4) ? 4 : \
>> + (n) & (1ULL << 3) ? 3 : \
>> + (n) & (1ULL << 2) ? 2 : \
>> +- (n) & (1ULL << 1) ? 1 : \
>> +- (n) & (1ULL << 0) ? 0 : \
>> +- ____ilog2_NaN() \
>> +- ) : \
>> ++ 1 ) : \
>> + (sizeof(n) <= 4) ? \
>> + __ilog2_u32(n) : \
>> + __ilog2_u64(n) \
>> +--
>> +2.12.2
>> +
>> diff --git a/meta/recipes-kernel/linux/linux-yocto_4.1.bb
>> b/meta/recipes-kernel/linux/linux-yocto_4.1.bb
>> index bf7f266ee6..f90d5159d5 100644
>> --- a/meta/recipes-kernel/linux/linux-yocto_4.1.bb
>> +++ b/meta/recipes-kernel/linux/linux-yocto_4.1.bb
>> @@ -24,6 +24,8 @@ SRCREV_meta ?=
>> "7140ddb86e4b01529185e6d4a606001ad152b8f3"
>> SRC_URI =
>> "git://git.yoctoproject.org/linux-yocto-4.1.git;name=machine;branch=${KBRANCH};
>> \
>>
>> git://git.yoctoproject.org/yocto-kernel-cache;type=kmeta;name=meta;branch=yocto-4.1;destsuffix=${KMETA}"
>>
>> +SRC_URI +=
>> "file://0001-give-up-on-gcc-ilog2-constant-optimizations.patch"
>> +
>> LINUX_VERSION ?= "4.1.38"
>>
>> PV = "${LINUX_VERSION}+git${SRCPV}"
>> --
>> 2.13.0
>>
>> --
>> _______________________________________________
>> Openembedded-core mailing list
>> Openembedded-core at lists.openembedded.org
>> http://lists.openembedded.org/mailman/listinfo/openembedded-core
>
>
>
>
> --
> "Thou shalt not follow the NULL pointer, for chaos and madness await thee at
> its end"
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