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Message-Id: <20210910234047.1019925-3-ndesaulniers@google.com>
Date: Fri, 10 Sep 2021 16:40:39 -0700
From: Nick Desaulniers <ndesaulniers@...gle.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
Nathan Chancellor <nathan@...nel.org>,
Masahiro Yamada <masahiroy@...nel.org>,
Joe Perches <joe@...ches.com>, Arnd Bergmann <arnd@...nel.org>,
Stephen Rothwell <sfr@...b.auug.org.au>, llvm@...ts.linux.dev,
linux-kernel@...r.kernel.org,
Nick Desaulniers <ndesaulniers@...gle.com>
Subject: [PATCH 02/10] compiler.h: drop fallback overflow checkers
Once upgrading the minimum supported version of GCC to 5.1, we can drop
the fallback code for !COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW.
Effectively a revert of
commit f0907827a8a9 ("compiler.h: enable builtin overflow checkers and
add fallback code")
Link: https://github.com/ClangBuiltLinux/linux/issues/1438#issuecomment-916745801
Suggested-by: Rasmus Villemoes <linux@...musvillemoes.dk>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
include/linux/compiler-clang.h | 13 ---
include/linux/compiler-gcc.h | 4 -
include/linux/overflow.h | 138 +---------------------------
tools/include/linux/compiler-gcc.h | 4 -
tools/include/linux/overflow.h | 140 +----------------------------
5 files changed, 6 insertions(+), 293 deletions(-)
diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index 49b0ac8b6fd3..3c4de9b6c6e3 100644
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -62,19 +62,6 @@
#define __no_sanitize_coverage
#endif
-/*
- * Not all versions of clang implement the type-generic versions
- * of the builtin overflow checkers. Fortunately, clang implements
- * __has_builtin allowing us to avoid awkward version
- * checks. Unfortunately, we don't know which version of gcc clang
- * pretends to be, so the macro may or may not be defined.
- */
-#if __has_builtin(__builtin_mul_overflow) && \
- __has_builtin(__builtin_add_overflow) && \
- __has_builtin(__builtin_sub_overflow)
-#define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
-#endif
-
#if __has_feature(shadow_call_stack)
# define __noscs __attribute__((__no_sanitize__("shadow-call-stack")))
#endif
diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
index cb9217fc60af..3f7f6fa0e051 100644
--- a/include/linux/compiler-gcc.h
+++ b/include/linux/compiler-gcc.h
@@ -128,10 +128,6 @@
#define __no_sanitize_coverage
#endif
-#if GCC_VERSION >= 50100
-#define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
-#endif
-
/*
* Turn individual warnings and errors on and off locally, depending
* on version.
diff --git a/include/linux/overflow.h b/include/linux/overflow.h
index 0f12345c21fb..4669632bd72b 100644
--- a/include/linux/overflow.h
+++ b/include/linux/overflow.h
@@ -6,12 +6,9 @@
#include <linux/limits.h>
/*
- * In the fallback code below, we need to compute the minimum and
- * maximum values representable in a given type. These macros may also
- * be useful elsewhere, so we provide them outside the
- * COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW block.
- *
- * It would seem more obvious to do something like
+ * We need to compute the minimum and maximum values representable in a given
+ * type. These macros may also be useful elsewhere. It would seem more obvious
+ * to do something like:
*
* #define type_min(T) (T)(is_signed_type(T) ? (T)1 << (8*sizeof(T)-1) : 0)
* #define type_max(T) (T)(is_signed_type(T) ? ((T)1 << (8*sizeof(T)-1)) - 1 : ~(T)0)
@@ -54,7 +51,6 @@ static inline bool __must_check __must_check_overflow(bool overflow)
return unlikely(overflow);
}
-#ifdef COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW
/*
* For simplicity and code hygiene, the fallback code below insists on
* a, b and *d having the same type (similar to the min() and max()
@@ -90,134 +86,6 @@ static inline bool __must_check __must_check_overflow(bool overflow)
__builtin_mul_overflow(__a, __b, __d); \
}))
-#else
-
-
-/* Checking for unsigned overflow is relatively easy without causing UB. */
-#define __unsigned_add_overflow(a, b, d) ({ \
- typeof(a) __a = (a); \
- typeof(b) __b = (b); \
- typeof(d) __d = (d); \
- (void) (&__a == &__b); \
- (void) (&__a == __d); \
- *__d = __a + __b; \
- *__d < __a; \
-})
-#define __unsigned_sub_overflow(a, b, d) ({ \
- typeof(a) __a = (a); \
- typeof(b) __b = (b); \
- typeof(d) __d = (d); \
- (void) (&__a == &__b); \
- (void) (&__a == __d); \
- *__d = __a - __b; \
- __a < __b; \
-})
-/*
- * If one of a or b is a compile-time constant, this avoids a division.
- */
-#define __unsigned_mul_overflow(a, b, d) ({ \
- typeof(a) __a = (a); \
- typeof(b) __b = (b); \
- typeof(d) __d = (d); \
- (void) (&__a == &__b); \
- (void) (&__a == __d); \
- *__d = __a * __b; \
- __builtin_constant_p(__b) ? \
- __b > 0 && __a > type_max(typeof(__a)) / __b : \
- __a > 0 && __b > type_max(typeof(__b)) / __a; \
-})
-
-/*
- * For signed types, detecting overflow is much harder, especially if
- * we want to avoid UB. But the interface of these macros is such that
- * we must provide a result in *d, and in fact we must produce the
- * result promised by gcc's builtins, which is simply the possibly
- * wrapped-around value. Fortunately, we can just formally do the
- * operations in the widest relevant unsigned type (u64) and then
- * truncate the result - gcc is smart enough to generate the same code
- * with and without the (u64) casts.
- */
-
-/*
- * Adding two signed integers can overflow only if they have the same
- * sign, and overflow has happened iff the result has the opposite
- * sign.
- */
-#define __signed_add_overflow(a, b, d) ({ \
- typeof(a) __a = (a); \
- typeof(b) __b = (b); \
- typeof(d) __d = (d); \
- (void) (&__a == &__b); \
- (void) (&__a == __d); \
- *__d = (u64)__a + (u64)__b; \
- (((~(__a ^ __b)) & (*__d ^ __a)) \
- & type_min(typeof(__a))) != 0; \
-})
-
-/*
- * Subtraction is similar, except that overflow can now happen only
- * when the signs are opposite. In this case, overflow has happened if
- * the result has the opposite sign of a.
- */
-#define __signed_sub_overflow(a, b, d) ({ \
- typeof(a) __a = (a); \
- typeof(b) __b = (b); \
- typeof(d) __d = (d); \
- (void) (&__a == &__b); \
- (void) (&__a == __d); \
- *__d = (u64)__a - (u64)__b; \
- ((((__a ^ __b)) & (*__d ^ __a)) \
- & type_min(typeof(__a))) != 0; \
-})
-
-/*
- * Signed multiplication is rather hard. gcc always follows C99, so
- * division is truncated towards 0. This means that we can write the
- * overflow check like this:
- *
- * (a > 0 && (b > MAX/a || b < MIN/a)) ||
- * (a < -1 && (b > MIN/a || b < MAX/a) ||
- * (a == -1 && b == MIN)
- *
- * The redundant casts of -1 are to silence an annoying -Wtype-limits
- * (included in -Wextra) warning: When the type is u8 or u16, the
- * __b_c_e in check_mul_overflow obviously selects
- * __unsigned_mul_overflow, but unfortunately gcc still parses this
- * code and warns about the limited range of __b.
- */
-
-#define __signed_mul_overflow(a, b, d) ({ \
- typeof(a) __a = (a); \
- typeof(b) __b = (b); \
- typeof(d) __d = (d); \
- typeof(a) __tmax = type_max(typeof(a)); \
- typeof(a) __tmin = type_min(typeof(a)); \
- (void) (&__a == &__b); \
- (void) (&__a == __d); \
- *__d = (u64)__a * (u64)__b; \
- (__b > 0 && (__a > __tmax/__b || __a < __tmin/__b)) || \
- (__b < (typeof(__b))-1 && (__a > __tmin/__b || __a < __tmax/__b)) || \
- (__b == (typeof(__b))-1 && __a == __tmin); \
-})
-
-
-#define check_add_overflow(a, b, d) __must_check_overflow( \
- __builtin_choose_expr(is_signed_type(typeof(a)), \
- __signed_add_overflow(a, b, d), \
- __unsigned_add_overflow(a, b, d)))
-
-#define check_sub_overflow(a, b, d) __must_check_overflow( \
- __builtin_choose_expr(is_signed_type(typeof(a)), \
- __signed_sub_overflow(a, b, d), \
- __unsigned_sub_overflow(a, b, d)))
-
-#define check_mul_overflow(a, b, d) __must_check_overflow( \
- __builtin_choose_expr(is_signed_type(typeof(a)), \
- __signed_mul_overflow(a, b, d), \
- __unsigned_mul_overflow(a, b, d)))
-
-#endif /* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW */
-
/** check_shl_overflow() - Calculate a left-shifted value and check overflow
*
* @a: Value to be shifted
diff --git a/tools/include/linux/compiler-gcc.h b/tools/include/linux/compiler-gcc.h
index 95c072b70d0e..a590a1dfafd9 100644
--- a/tools/include/linux/compiler-gcc.h
+++ b/tools/include/linux/compiler-gcc.h
@@ -38,7 +38,3 @@
#endif
#define __printf(a, b) __attribute__((format(printf, a, b)))
#define __scanf(a, b) __attribute__((format(scanf, a, b)))
-
-#if GCC_VERSION >= 50100
-#define COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW 1
-#endif
diff --git a/tools/include/linux/overflow.h b/tools/include/linux/overflow.h
index 8712ff70995f..dcb0c1bf6866 100644
--- a/tools/include/linux/overflow.h
+++ b/tools/include/linux/overflow.h
@@ -5,12 +5,9 @@
#include <linux/compiler.h>
/*
- * In the fallback code below, we need to compute the minimum and
- * maximum values representable in a given type. These macros may also
- * be useful elsewhere, so we provide them outside the
- * COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW block.
- *
- * It would seem more obvious to do something like
+ * We need to compute the minimum and maximum values representable in a given
+ * type. These macros may also be useful elsewhere. It would seem more obvious
+ * to do something like:
*
* #define type_min(T) (T)(is_signed_type(T) ? (T)1 << (8*sizeof(T)-1) : 0)
* #define type_max(T) (T)(is_signed_type(T) ? ((T)1 << (8*sizeof(T)-1)) - 1 : ~(T)0)
@@ -36,8 +33,6 @@
#define type_max(T) ((T)((__type_half_max(T) - 1) + __type_half_max(T)))
#define type_min(T) ((T)((T)-type_max(T)-(T)1))
-
-#ifdef COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW
/*
* For simplicity and code hygiene, the fallback code below insists on
* a, b and *d having the same type (similar to the min() and max()
@@ -73,135 +68,6 @@
__builtin_mul_overflow(__a, __b, __d); \
})
-#else
-
-
-/* Checking for unsigned overflow is relatively easy without causing UB. */
-#define __unsigned_add_overflow(a, b, d) ({ \
- typeof(a) __a = (a); \
- typeof(b) __b = (b); \
- typeof(d) __d = (d); \
- (void) (&__a == &__b); \
- (void) (&__a == __d); \
- *__d = __a + __b; \
- *__d < __a; \
-})
-#define __unsigned_sub_overflow(a, b, d) ({ \
- typeof(a) __a = (a); \
- typeof(b) __b = (b); \
- typeof(d) __d = (d); \
- (void) (&__a == &__b); \
- (void) (&__a == __d); \
- *__d = __a - __b; \
- __a < __b; \
-})
-/*
- * If one of a or b is a compile-time constant, this avoids a division.
- */
-#define __unsigned_mul_overflow(a, b, d) ({ \
- typeof(a) __a = (a); \
- typeof(b) __b = (b); \
- typeof(d) __d = (d); \
- (void) (&__a == &__b); \
- (void) (&__a == __d); \
- *__d = __a * __b; \
- __builtin_constant_p(__b) ? \
- __b > 0 && __a > type_max(typeof(__a)) / __b : \
- __a > 0 && __b > type_max(typeof(__b)) / __a; \
-})
-
-/*
- * For signed types, detecting overflow is much harder, especially if
- * we want to avoid UB. But the interface of these macros is such that
- * we must provide a result in *d, and in fact we must produce the
- * result promised by gcc's builtins, which is simply the possibly
- * wrapped-around value. Fortunately, we can just formally do the
- * operations in the widest relevant unsigned type (u64) and then
- * truncate the result - gcc is smart enough to generate the same code
- * with and without the (u64) casts.
- */
-
-/*
- * Adding two signed integers can overflow only if they have the same
- * sign, and overflow has happened iff the result has the opposite
- * sign.
- */
-#define __signed_add_overflow(a, b, d) ({ \
- typeof(a) __a = (a); \
- typeof(b) __b = (b); \
- typeof(d) __d = (d); \
- (void) (&__a == &__b); \
- (void) (&__a == __d); \
- *__d = (u64)__a + (u64)__b; \
- (((~(__a ^ __b)) & (*__d ^ __a)) \
- & type_min(typeof(__a))) != 0; \
-})
-
-/*
- * Subtraction is similar, except that overflow can now happen only
- * when the signs are opposite. In this case, overflow has happened if
- * the result has the opposite sign of a.
- */
-#define __signed_sub_overflow(a, b, d) ({ \
- typeof(a) __a = (a); \
- typeof(b) __b = (b); \
- typeof(d) __d = (d); \
- (void) (&__a == &__b); \
- (void) (&__a == __d); \
- *__d = (u64)__a - (u64)__b; \
- ((((__a ^ __b)) & (*__d ^ __a)) \
- & type_min(typeof(__a))) != 0; \
-})
-
-/*
- * Signed multiplication is rather hard. gcc always follows C99, so
- * division is truncated towards 0. This means that we can write the
- * overflow check like this:
- *
- * (a > 0 && (b > MAX/a || b < MIN/a)) ||
- * (a < -1 && (b > MIN/a || b < MAX/a) ||
- * (a == -1 && b == MIN)
- *
- * The redundant casts of -1 are to silence an annoying -Wtype-limits
- * (included in -Wextra) warning: When the type is u8 or u16, the
- * __b_c_e in check_mul_overflow obviously selects
- * __unsigned_mul_overflow, but unfortunately gcc still parses this
- * code and warns about the limited range of __b.
- */
-
-#define __signed_mul_overflow(a, b, d) ({ \
- typeof(a) __a = (a); \
- typeof(b) __b = (b); \
- typeof(d) __d = (d); \
- typeof(a) __tmax = type_max(typeof(a)); \
- typeof(a) __tmin = type_min(typeof(a)); \
- (void) (&__a == &__b); \
- (void) (&__a == __d); \
- *__d = (u64)__a * (u64)__b; \
- (__b > 0 && (__a > __tmax/__b || __a < __tmin/__b)) || \
- (__b < (typeof(__b))-1 && (__a > __tmin/__b || __a < __tmax/__b)) || \
- (__b == (typeof(__b))-1 && __a == __tmin); \
-})
-
-
-#define check_add_overflow(a, b, d) \
- __builtin_choose_expr(is_signed_type(typeof(a)), \
- __signed_add_overflow(a, b, d), \
- __unsigned_add_overflow(a, b, d))
-
-#define check_sub_overflow(a, b, d) \
- __builtin_choose_expr(is_signed_type(typeof(a)), \
- __signed_sub_overflow(a, b, d), \
- __unsigned_sub_overflow(a, b, d))
-
-#define check_mul_overflow(a, b, d) \
- __builtin_choose_expr(is_signed_type(typeof(a)), \
- __signed_mul_overflow(a, b, d), \
- __unsigned_mul_overflow(a, b, d))
-
-
-#endif /* COMPILER_HAS_GENERIC_BUILTIN_OVERFLOW */
-
/**
* array_size() - Calculate size of 2-dimensional array.
*
--
2.33.0.309.g3052b89438-goog
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