On 14 July 2017 at 10:25, Arnd Bergmann <arnd@xxxxxxxx> wrote:
> gcc warns when MODULES_VADDR/END is defined to the same value as
> VMALLOC_START/VMALLOC_END, e.g. on x86-32:
>
> fs/proc/kcore.c: In function ‘add_modules_range’:
> fs/proc/kcore.c:622:161: error: self-comparison always evaluates to false [-Werror=tautological-compare]
> if (/*MODULES_VADDR != VMALLOC_START && */MODULES_END != VMALLOC_END) {
>
Does it occur for subtraction as well? Or only for comparison?
> The code is correct as it is required for most other configurations.
> The best workaround I found for shutting up that warning is to make
> it a little more complex by adding a temporary variable. The compiler
> will still optimize away the code as it finds the two to be identical,
> but it no longer warns because it doesn't condider the comparison
> "tautological" any more.
>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> ---
> fs/proc/kcore.c | 10 ++++++----
> 1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c
> index 45629f4b5402..c503ad657c46 100644
> --- a/fs/proc/kcore.c
> +++ b/fs/proc/kcore.c
> @@ -620,12 +620,14 @@ static void __init proc_kcore_text_init(void)
> /*
> * MODULES_VADDR has no intersection with VMALLOC_ADDR.
> */
> -struct kcore_list kcore_modules;
> +static struct kcore_list kcore_modules;
> static void __init add_modules_range(void)
> {
> - if (MODULES_VADDR != VMALLOC_START && MODULES_END != VMALLOC_END) {
> - kclist_add(&kcore_modules, (void *)MODULES_VADDR,
> - MODULES_END - MODULES_VADDR, KCORE_VMALLOC);
> + void *start = (void *)MODULES_VADDR;
> + size_t len = MODULES_END - MODULES_VADDR;
> +
> + if (start != (void *)VMALLOC_START && len != VMALLOC_END - VMALLOC_START) {
> + kclist_add(&kcore_modules, start, len, KCORE_VMALLOC);
> }
> }
> #else
> --
> 2.9.0
>
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