fix build error when compiling with gcc7

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=72785

2 files changed, 130 insertions, 0 deletions

diff --git a/PKGBUILD b/PKGBUILD
index c529773b6554..b8682d9cfe1a 100644
--- a/PKGBUILD
+++ b/PKGBUILD
@@ -19,10 +19,12 @@ source=("git+https://github.com/GalliumOS/linux.git#branch=v${pkgver}"
         # standard config files for mkinitcpio ramdisk
         "${pkgbase}.preset"
         "dmi_product_family.diff"
+        "gcc7_compatibility_fix.diff"
         "cherryview-pinctrl.diff")
 sha256sums=('SKIP'
             '7f9b77e1ac3b59453f6bb3858d0549c3022e6ae93ca3978427d96ae23f87e451'
             '949990c191638f63f1906dbd7f4be8b82b40da94ef873b15af68c9e726b13c51'
+            '2d6a5e0a87cafeda120a509d90626579c0e857d3b277ebf1a0f5824c9376ddaf'
             'SKIP')
 
 _kernelname=${pkgbase#linux}
@@ -30,6 +32,7 @@ _kernelname=${pkgbase#linux}
 prepare() {
   cd "${_srcname}"
 
+  patch -p1 < ${srcdir}/gcc7_compatibility_fix.diff
   patch -p1 < ${srcdir}/dmi_product_family.diff
 
   cp $srcdir/cherryview-pinctrl.diff galliumos/diffs/
diff --git a/gcc7_compatibility_fix.diff b/gcc7_compatibility_fix.diff
new file mode 100644
index 000000000000..ce4c2b8fc103
--- /dev/null
+++ b/gcc7_compatibility_fix.diff
@@ -0,0 +1,127 @@
+From 474c90156c8dcc2fa815e6716cc9394d7930cb9c Mon Sep 17 00:00:00 2001
+From: Linus Torvalds <torvalds@linux-foundation.org>
+Date: Thu, 2 Mar 2017 12:17:22 -0800
+Subject: 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@redhat.com>
+Cc: John Stultz <john.stultz@linaro.org>,
+Cc: Thomas Gleixner <tglx@linutronix.de>
+Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
+Signed-off-by: Linus Torvalds <torvalds@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 ef3d4f6..c373295 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)				\
+-- 
+cgit v1.1
+