[meta-intel] [PATCH] linux-intel: Backport patch to fix build with gcc7
Saul Wold
sgw at linux.intel.com
Tue Apr 18 07:46:23 PDT 2017
On Mon, 2017-04-17 at 23:40 +0000, Khem Raj wrote:
> Signed-off-by: Khem Raj <raj.khem at gmail.com>
> ---
> ...ve-up-on-gcc-ilog2-constant-optimizations.patch | 127
> +++++++++++++++++++++
> common/recipes-kernel/linux/linux-intel_4.9.bb | 5 +-
> 2 files changed, 130 insertions(+), 2 deletions(-)
> create mode 100644 common/recipes-kernel/linux/files/0001-give-up-
> on-gcc-ilog2-constant-optimizations.patch
>
> diff --git a/common/recipes-kernel/linux/files/0001-give-up-on-gcc-
> ilog2-constant-optimizations.patch b/common/recipes-
> kernel/linux/files/0001-give-up-on-gcc-ilog2-constant-
> optimizations.patch
> new file mode 100644
> index 0000000..481e1b6
> --- /dev/null
> +++ b/common/recipes-kernel/linux/files/0001-give-up-on-gcc-ilog2-
> constant-optimizations.patch
> @@ -0,0 +1,127 @@
> +From c2812ad30bf55b62a5aefd3b1602a9c5d7f2dccc 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
> +
> +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>
> +---
> + 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 fd7ff3d..f38fae2 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 4144666..d5677d3 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) \
> +--
> +1.9.1
> +
> diff --git a/common/recipes-kernel/linux/linux-intel_4.9.bb
> b/common/recipes-kernel/linux/linux-intel_4.9.bb
> index 46821a9..d26a6ad 100644
> --- a/common/recipes-kernel/linux/linux-intel_4.9.bb
> +++ b/common/recipes-kernel/linux/linux-intel_4.9.bb
> @@ -6,8 +6,9 @@ SRCREV_machine ?=
> "6f425e57c6afaed5d61cd9b8abe898bae97f9374"
> SRCREV_meta ?= "b65e9b6153237e3ee898a01bc418c12f7404a681"
>
> SRC_URI = "git://github.com/01org/linux-intel-
> 4.9.git;protocol=https;name=machine;branch=${KBRANCH}; \
> - git://git.yoctoproject.org/yocto-kernel-
> cache;type=kmeta;name=meta;branch=yocto-4.9;destsuffix=${KMETA}"
> -
> + git://git.yoctoproject.org/yocto-kernel-
> cache;type=kmeta;name=meta;branch=yocto-4.9;destsuffix=${KMETA} \
> + file://0001-give-up-on-gcc-ilog2-constant-
> optimizations.patch \
> +"
> LINUX_VERSION ?= "4.9.15"
>
Timing is, this patch failed due to a kernel SRCREV Update that pushed
this to 4.9.20, I am also concerned about adding this patch just before
the release, can this wait until after M4 BSP releases?
I have also submitted this to the linux-intel kernel, so it might
appear there directly.
Thanks
Sau!
> PV = "${LINUX_VERSION}+git${SRCPV}"
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