From b8534f767c4b81fb11376e9d7ffb48ace6889539 Mon Sep 17 00:00:00 2001 From: Julius Werner Date: Fri, 14 Jul 2017 14:14:11 -0700 Subject: assert: Add new dead_code() macro to assert dead code paths This patch adds a new kind of compile-time assertion based on Linux' compiletime_assert(). The difference to the existing use of _Static_assert() in coreboot (which should continue to be used where appropriate) is that this new assertion only hits if the call to it is not optimized out at compile time. It is therefore ideal to assert that certain code paths are not included in the image if a certain Kconfig option is (not) set. For example, assert(!IS_ENABLED(CONFIG_THAT_MAKES_THIS_INAPPROPRIATE)); can be rewritten as if (!IS_ENABLED(CONFIG_THAT_MAKES_THIS_INAPPROPRIATE)) dead_code("This code shouldn't be built for config X"); to turn it into a compile-time check. Change-Id: Ida2911e2e4b3191a00d09231b493bf755e6f0fcb Signed-off-by: Julius Werner Reviewed-on: https://review.coreboot.org/20585 Reviewed-by: Aaron Durbin Tested-by: build bot (Jenkins) Reviewed-by: Paul Menzel --- src/include/assert.h | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) (limited to 'src') diff --git a/src/include/assert.h b/src/include/assert.h index 90cc2a8b18..a4ae39f606 100644 --- a/src/include/assert.h +++ b/src/include/assert.h @@ -37,4 +37,25 @@ #define assert(statement) ASSERT(statement) +/* + * These macros can be used to assert that a certain branch of code is dead and + * will be compile-time eliminated. This differs from _Static_assert(), which + * will generate a compiler error even if the scope it was called from is dead + * code. This may be useful to double-check things like constants that are only + * valid if a certain Kconfig option is set. + */ +#define __dead_code(message, line) do { \ + __attribute__((error(#message " in " __FILE__ ":" #line))) \ + extern void dead_code_assertion_failed_##line(void); \ + dead_code_assertion_failed_##line(); \ +} while (0) +#define _dead_code(message, line) __dead_code(message, line) +#define dead_code(message) _dead_code(message, __LINE__) + +/* This can be used in the context of an expression of type 'type'. */ +#define dead_code_t(type, message) ({ \ + dead_code(message); \ + *(type *)(uintptr_t)0; \ +}) + #endif // __ASSERT_H__ -- cgit v1.2.3