From e7300e75b51a7e7d4e81975b4be7a6c65f9a8286 Mon Sep 17 00:00:00 2001 From: Aaron Ballman Date: Wed, 18 Jan 2023 08:49:45 -0500 Subject: Diagnose extensions in 'offsetof' https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm made very clear that it is an UB having type definitions with in offsetof. Clang supports defining a type as the first argument as a conforming extension due to how many projects use the construct in C99 and earlier to calculate the alignment of a type. GCC also supports defining a type as the first argument. This adds extension warnings and documentation for the functionality Clang explicitly supports. Fixes #57065 Reverts the revert of 39da55e8f548a11f7dadefa73ea73d809a5f1729 Co-authored-by: Yingchi Long Co-authored-by: Aaron Ballman Differential Revision: https://reviews.llvm.org/D133574 --- clang/test/Sema/offsetof.c | 19 +++++++++++-------- 1 file changed, 11 insertions(+), 8 deletions(-) (limited to 'clang/test/Sema/offsetof.c') diff --git a/clang/test/Sema/offsetof.c b/clang/test/Sema/offsetof.c index 3a5ddc4..8fd9ad6 100644 --- a/clang/test/Sema/offsetof.c +++ b/clang/test/Sema/offsetof.c @@ -5,35 +5,38 @@ typedef struct P { int i; float f; } PT; struct external_sun3_core { - unsigned c_regs; + unsigned c_regs; PT X[100]; - + }; +// Ensure the builtin works as a constant expression +int i = offsetof(PT, f); + void swap(void) { int x; x = offsetof(struct external_sun3_core, c_regs); x = __builtin_offsetof(struct external_sun3_core, X[42].f); - + x = __builtin_offsetof(struct external_sun3_core, X[42].f2); // expected-error {{no member named 'f2'}} x = __builtin_offsetof(int, X[42].f2); // expected-error {{offsetof requires struct}} - + int a[__builtin_offsetof(struct external_sun3_core, X) == 4 ? 1 : -1]; int b[__builtin_offsetof(struct external_sun3_core, X[42]) == 340 ? 1 : -1]; int c[__builtin_offsetof(struct external_sun3_core, X[42].f2) == 344 ? 1 : -1]; // expected-error {{no member named 'f2'}} -} +} extern int f(void); -struct s1 { int a; }; +struct s1 { int a; }; int v1 = offsetof (struct s1, a) == 0 ? 0 : f(); -struct s2 { int a; }; +struct s2 { int a; }; int v2 = (int)(&((struct s2 *) 0)->a) == 0 ? 0 : f(); -struct s3 { int a; }; +struct s3 { int a; }; int v3 = __builtin_offsetof(struct s3, a) == 0 ? 0 : f(); // PR3396 -- cgit v1.1