From 9c7b53b21fb1df20f85e3822160b4687f98ff7b3 Mon Sep 17 00:00:00 2001 From: Marc Herbert Date: Thu, 24 Apr 2025 19:40:35 +0000 Subject: [PATCH] compiler_types.h: fix "unused variable" in __compiletime_assert() This refines commit c03567a8e8d5 ("include/linux/compiler.h: don't perform compiletime_assert with -O0") and restores #ifdef __OPTIMIZE__ symmetry by evaluating the 'condition' variable in both compile-time variants of __compiletimeassert(). As __OPTIMIZE__ is always true by default, this commit does not change anything by default. But it fixes warnings with _non-default_ CFLAGS like for instance this: make CFLAGS_tcp.o='-Og -U__OPTIMIZE__' from net/ipv4/tcp.c:273: include/net/sch_generic.h: In function `qdisc_cb_private_validate': include/net/sch_generic.h:511:30: error: unused variable `qcb' [-Werror=unused-variable] { struct qdisc_skb_cb *qcb; BUILD_BUG_ON(sizeof(skb->cb) < sizeof(*qcb)); ... } [akpm@linux-foundation.org: regularize comment layout, reflow comment] Link: https://lkml.kernel.org/r/20250424194048.652571-1-marc.herbert@linux.intel.com Signed-off-by: Marc Herbert Cc: Alexander Potapenko Cc: Changbin Du Cc: Jan Hendrik Farr Cc: Macro Elver Cc: Miguel Ojeda Cc: Tony Ambardar Cc: Uros Bizjak Cc: Kees Cook Signed-off-by: Andrew Morton --- include/linux/compiler_types.h | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index 501cffddc2f41..1f2eee8331d35 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -525,6 +525,12 @@ struct ftrace_likely_data { sizeof(t) == sizeof(int) || sizeof(t) == sizeof(long)) #ifdef __OPTIMIZE__ +/* + * #ifdef __OPTIMIZE__ is only a good approximation; for instance "make + * CFLAGS_foo.o=-Og" defines __OPTIMIZE__, does not elide the conditional code + * and can break compilation with wrong error message(s). Combine with + * -U__OPTIMIZE__ when needed. + */ # define __compiletime_assert(condition, msg, prefix, suffix) \ do { \ /* \ @@ -538,7 +544,7 @@ struct ftrace_likely_data { prefix ## suffix(); \ } while (0) #else -# define __compiletime_assert(condition, msg, prefix, suffix) do { } while (0) +# define __compiletime_assert(condition, msg, prefix, suffix) ((void)(condition)) #endif #define _compiletime_assert(condition, msg, prefix, suffix) \ -- 2.47.2