Re: [flashrom] [PATCH] Fix undefined behavior in some preprocessor define checks

[Carl-Daniel Hailfinger]

Hi Stefan,

this patch includes [flashrom] [PATCH] Fix undefined behavior in OS defines
Is that intentional?

One minor nitpick: Using "#ifdef IS_LINUX" will be true on all 
platforms with that change. Admittedly it probably was undefined
behaviour before, so this is an improvement. I wonder if we should add a
comment before the IS_ and USE_ #defines to tell people to always use
them with #if and never with if defined() or #ifdef.

Acked-by: Carl-Daniel Hailfinger

Regards,
Carl-Daniel

On 02.12.2016 01:49, Stefan Tauner wrote:
> The macro below (as used it was used previously) would produce
> undefined behavior when used as expression in an
> #if preprocessor directive:
> #define IS_LINUX (defined(__gnu_linux__) || defined(__linux__))
>
> This patch replaces all such statements with a more verbose but
> well-defined #if/#define x 1/#else/#define x 0/#endif
>
> Found by clang (warning introduced in r258128), reported by Idwer.
> Signed-off-by: Stefan Tauner
>
> hwaccess.c | 18 +++++++++++++++---
>  platform.h | 19 +++++++++++++++----
>  2 files changed, 30 insertions(+), 7 deletions(-)
>
> diff --git a/hwaccess.c b/hwaccess.c
> index 1901ee6..80852e7 100644
> --- a/hwaccess.c
> +++ b/hwaccess.c
> @@ -37,9 +37,21 @@
>  #error "Unknown operating system"
>  #endif
>
> -#define USE_IOPL	(IS_LINUX || IS_MACOSX || defined(__NetBSD__) || defined(__OpenBSD__))
> -#define USE_DEV_IO	(defined(__FreeBSD__) || defined(__FreeBSD_kernel__) || defined(__DragonFly__))
> -#define USE_IOPERM	(defined(__gnu_hurd__))
> +#if (IS_LINUX || IS_MACOSX || defined(__NetBSD__) || defined(__OpenBSD__))
> #define USE_IOPL (1)
>
> +#else
> #define USE_IOPL (0)
>
> +#endif
> +#if (defined(__FreeBSD__) || defined(__FreeBSD_kernel__) || defined(__DragonFly__))
> #define USE_DEV_IO (1)
>
> +#else
> #define USE_DEV_IO (0)
>
> +#endif
> +#if (defined(__gnu_hurd__))
> #define USE_IOPERM (1)
>
> +#else
> #define USE_IOPERM (0)
>
> +#endif
>
> #if USE_IOPERM
>  #include <sys/io.h>
> diff --git a/platform.h b/platform.h
> index c5a52ef..2785753 100644
> --- a/platform.h
> +++ b/platform.h
> @@ -24,10 +24,21 @@
>  #ifndef __PLATFORM_H__
>  #define __PLATFORM_H__ 1
>
> -// Helper defines for operating systems
> -#define IS_LINUX	(defined(__gnu_linux__) || defined(__linux__))
> -#define IS_MACOSX	(defined(__APPLE__) && defined(__MACH__)) /* yes, both. */
> -#define IS_WINDOWS	(defined(_WIN32) || defined(_WIN64) || defined(__WIN32__) || defined(__WINDOWS__))
> +#if (defined(__gnu_linux__) || defined(__linux__))
> #define IS_LINUX (1)
>
> +#else
> #define IS_LINUX (0)
>
> +#endif
> +#if (defined(__APPLE__) && defined(__MACH__)) /* yes, both. */
> #define IS_MACOSX (1)
>
> +#else
> #define IS_MACOSX (0)
>
> +#endif
> +#if (defined(_WIN32) || defined(_WIN64) || defined(__WIN32__) || defined(__WINDOWS__))
> #define IS_WINDOWS (1)
>
> +#else
> #define IS_WINDOWS (0)
>
> +#endif
>
> // Likewise for target architectures
>  #if defined (__i386__) || defined (__x86_64__) || defined(__amd64__)