[OE-core] [PATCH 7/7] linux-yocto_4.1.bb: Fix build with gcc7
Bruce Ashfield
bruce.ashfield at gmail.com
Sat May 13 15:45:52 UTC 2017
I already have this queued, I'm just not sending any kernel pull requests
while
the release is finalizing.
So please, do not queue or merge this change.
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 ?= "7140ddb86e4b01529185e6d4a60600
> 1ad152b8f3"
> 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
>
> --
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> Openembedded-core at lists.openembedded.org
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>
--
"Thou shalt not follow the NULL pointer, for chaos and madness await thee
at its end"
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