From ef0f4e834c6634b4ef5ae6117c74c58db4e7c1c0 Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Tue, 18 May 2021 11:19:46 +0200 Subject: [PATCH 1/2] build_bug.h: add wrapper for _Static_assert [Linux commit 6bab69c65013bed5fce9f101a64a84d0385b3946] BUILD_BUG_ON() is a little annoying, since it cannot be used outside function scope. So one cannot put assertions about the sizeof() a struct next to the struct definition, but has to hide that in some more or less arbitrary function. Since gcc 4.6 (which is now also the required minimum), there is support for the C11 _Static_assert in all C modes, including gnu89. So add a simple wrapper for that. _Static_assert() requires a message argument, which is usually quite redundant (and I believe that bug got fixed at least in newer C++ standards), but we can easily work around that with a little macro magic, making it optional. For example, adding static_assert(sizeof(struct printf_spec) == 8); in vsprintf.c and modifying that struct to violate it, one gets ./include/linux/build_bug.h:78:41: error: static assertion failed: "sizeof(struct printf_spec) == 8" #define __static_assert(expr, msg, ...) _Static_assert(expr, "" msg "") godbolt.org suggests that _Static_assert() has been support by clang since at least 3.0.0. Signed-off-by: Rasmus Villemoes Reviewed-by: Simon Glass --- include/linux/build_bug.h | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/include/linux/build_bug.h b/include/linux/build_bug.h index b7d22d6000..9c7088bafa 100644 --- a/include/linux/build_bug.h +++ b/include/linux/build_bug.h @@ -79,6 +79,25 @@ */ #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed") +/** + * static_assert - check integer constant expression at build time + * + * static_assert() is a wrapper for the C11 _Static_assert, with a + * little macro magic to make the message optional (defaulting to the + * stringification of the tested expression). + * + * Contrary to BUILD_BUG_ON(), static_assert() can be used at global + * scope, but requires the expression to be an integer constant + * expression (i.e., it is not enough that __builtin_constant_p() is + * true for expr). + * + * Also note that BUILD_BUG_ON() fails the build if the condition is + * true, while static_assert() fails the build if the expression is + * false. + */ +#define static_assert(expr, ...) __static_assert(expr, ##__VA_ARGS__, #expr) +#define __static_assert(expr, msg, ...) _Static_assert(expr, msg) + #endif /* __CHECKER__ */ #endif /* _LINUX_BUILD_BUG_H */ From ee3a46a437315cbbbc746890c2cf8eea5dd7f1e7 Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Tue, 18 May 2021 11:19:47 +0200 Subject: [PATCH 2/2] global-data.h: add build-time sanity check of sizeof(struct global_data) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The layout and contents of struct global_data depends on a lot of CONFIG_* preprocessor macros, not all of which are entirely converted to Kconfig - not to mention weird games played here and there. This can result in one translation unit using one definition of struct global_data while the actual layout is another. That can be very hard to debug. But we already have a mechanism that can help catch such bugs at build time, namely the asm-offsets machinery which is necessary anyway to provide assembly code with the necessary constants. So make sure that every C translation unit that include global_data.h actually sees the same size of struct global_data as that which was seen by the asm-offsets.c TU. It is likely that this patch will break the build of some boards. For example, without the patch from Matt Merhar (https://lists.denx.de/pipermail/u-boot/2021-May/450135.html) or some other fix, this breaks P2041RDB_defconfig: CC arch/powerpc/lib/traps.o AS arch/powerpc/cpu/mpc85xx/start.o In file included from include/asm-generic/global_data.h:26, from ./arch/powerpc/include/asm/global_data.h:109, from include/init.h:21, from arch/powerpc/lib/traps.c:7: include/linux/build_bug.h:99:41: error: static assertion failed: "sizeof(struct global_data) == GD_SIZE" 99 | #define __static_assert(expr, msg, ...) _Static_assert(expr, msg) | ^~~~~~~~~~~~~~ include/linux/build_bug.h:98:34: note: in expansion of macro ‘__static_assert’ 98 | #define static_assert(expr, ...) __static_assert(expr, ##__VA_ARGS__, #expr) | ^~~~~~~~~~~~~~~ include/asm-generic/global_data.h:470:1: note: in expansion of macro ‘static_assert’ 470 | static_assert(sizeof(struct global_data) == GD_SIZE); | ^~~~~~~~~~~~~ make[1]: *** [scripts/Makefile.build:266: arch/powerpc/lib/traps.o] Error 1 make: *** [Makefile:1753: arch/powerpc/lib] Error 2 make: *** Waiting for unfinished jobs.... Signed-off-by: Rasmus Villemoes Reviewed-by: Simon Glass --- include/asm-generic/global_data.h | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/include/asm-generic/global_data.h b/include/asm-generic/global_data.h index e278d4c941..5fed4db23f 100644 --- a/include/asm-generic/global_data.h +++ b/include/asm-generic/global_data.h @@ -23,6 +23,8 @@ #include #include #include +#include +#include struct acpi_ctx; struct driver_rt; @@ -464,6 +466,9 @@ struct global_data { char *smbios_version; #endif }; +#ifndef DO_DEPS_ONLY +static_assert(sizeof(struct global_data) == GD_SIZE); +#endif /** * gd_board_type() - retrieve board type