Merge tag 'vla-v4.20-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux

Pull VLA removal from Kees Cook:
 "Globally warn on VLA use.

  This turns on "-Wvla" globally now that the last few trees with their
  VLA removals have landed (crypto, block, net, and powerpc).

  Arnd mentioned that there may be a couple more VLAs hiding in
  hard-to-find randconfigs, but nothing big has shaken out in the last
  month or so in linux-next.

  We should be basically VLA-free now! Wheee. :)

  Summary:

   - Remove unused fallback for BUILD_BUG_ON (which technically contains
     a VLA)

   - Lift -Wvla to the top-level Makefile"

* tag 'vla-v4.20-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/kees/linux:
  Makefile: Globally enable VLA warning
  compiler.h: give up __compiletime_assert_fallback()

5 files changed, 7 insertions, 18 deletions

diff --git a/Makefile b/Makefile
index eb73f062e9e9..9aa352b38815 100644
--- a/Makefile
+++ b/Makefile
@@ -801,6 +801,9 @@ NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)
 # warn about C99 declaration after statement
 KBUILD_CFLAGS += -Wdeclaration-after-statement
 
+# Variable Length Arrays (VLAs) should not be used anywhere in the kernel
+KBUILD_CFLAGS += $(call cc-option,-Wvla)
+
 # disable pointer signed / unsigned warnings in gcc 4.0
 KBUILD_CFLAGS += -Wno-pointer-sign
 
diff --git a/drivers/gpu/drm/i915/Makefile b/drivers/gpu/drm/i915/Makefile
index 5794f102f9b8..1c2857f13ad4 100644
--- a/drivers/gpu/drm/i915/Makefile
+++ b/drivers/gpu/drm/i915/Makefile
@@ -12,7 +12,7 @@
 # Note the danger in using -Wall -Wextra is that when CI updates gcc we
 # will most likely get a sudden build breakage... Hopefully we will fix
 # new warnings before CI updates!
-subdir-ccflags-y := -Wall -Wextra -Wvla
+subdir-ccflags-y := -Wall -Wextra
 subdir-ccflags-y += $(call cc-disable-warning, unused-parameter)
 subdir-ccflags-y += $(call cc-disable-warning, type-limits)
 subdir-ccflags-y += $(call cc-disable-warning, missing-field-initializers)
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 1921545c6351..4170fcee5adb 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -344,29 +344,14 @@ static inline void *offset_to_ptr(const int *off)
 #endif
 #ifndef __compiletime_error
 # define __compiletime_error(message)
-/*
- * Sparse complains of variable sized arrays due to the temporary variable in
- * __compiletime_assert. Unfortunately we can't just expand it out to make
- * sparse see a constant array size without breaking compiletime_assert on old
- * versions of GCC (e.g. 4.2.4), so hide the array from sparse altogether.
- */
-# ifndef __CHECKER__
-#  define __compiletime_error_fallback(condition) \
-	do { ((void)sizeof(char[1 - 2 * condition])); } while (0)
-# endif
-#endif
-#ifndef __compiletime_error_fallback
-# define __compiletime_error_fallback(condition) do { } while (0)
 #endif
 
 #ifdef __OPTIMIZE__
 # define __compiletime_assert(condition, msg, prefix, suffix)		\
 	do {								\
-		int __cond = !(condition);				\
 		extern void prefix ## suffix(void) __compiletime_error(msg); \
-		if (__cond)						\
+		if (!(condition))					\
 			prefix ## suffix();				\
-		__compiletime_error_fallback(__cond);			\
 	} while (0)
 #else
 # define __compiletime_assert(condition, msg, prefix, suffix) do { } while (0)
diff --git a/lib/Makefile b/lib/Makefile
index 3d341f59f756..988949c4fd3a 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -53,7 +53,9 @@ obj-$(CONFIG_TEST_HASH) += test_hash.o test_siphash.o
 obj-$(CONFIG_TEST_IDA) += test_ida.o
 obj-$(CONFIG_TEST_KASAN) += test_kasan.o
 CFLAGS_test_kasan.o += -fno-builtin
+CFLAGS_test_kasan.o += $(call cc-disable-warning, vla)
 obj-$(CONFIG_TEST_UBSAN) += test_ubsan.o
+CFLAGS_test_ubsan.o += $(call cc-disable-warning, vla)
 UBSAN_SANITIZE_test_ubsan.o := y
 obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
 obj-$(CONFIG_TEST_LIST_SORT) += test_list_sort.o
diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
index 8d5357053f86..24b2fb1d1297 100644
--- a/scripts/Makefile.extrawarn
+++ b/scripts/Makefile.extrawarn
@@ -52,7 +52,6 @@ warning-3 += -Wpointer-arith
 warning-3 += -Wredundant-decls
 warning-3 += -Wswitch-default
 warning-3 += $(call cc-option, -Wpacked-bitfield-compat)
-warning-3 += $(call cc-option, -Wvla)
 
 warning := $(warning-$(findstring 1, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)))
 warning += $(warning-$(findstring 2, $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)))