[PATCH v2] kernel/extable: Use address-of operator on section symbols

[PATCH v2] kernel/extable: Use address-of operator on section symbols

[Nathan Chancellor]

Clang warns:

../kernel/extable.c:37:52: warning: array comparison always evaluates to
a constant [-Wtautological-compare]
        if (main_extable_sort_needed && __stop___ex_table > __start___ex_table) {
                                                          ^
1 warning generated.

These are not true arrays, they are linker defined symbols, which are
just addresses. Using the address of operator silences the warning and
does not change the resulting assembly with either clang/ld.lld or
gcc/ld (tested with diff + objdump -Dr).

Link: https://github.com/ClangBuiltLinux/linux/issues/892
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---

v1 -> v2: https://lore.kernel.org/lkml/20200219045423.54190-3-natechancellor@gmail.com/

* No longer a series because there is no prerequisite patch.
* Use address-of operator instead of casting to unsigned long.

 kernel/extable.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/extable.c b/kernel/extable.c
index a0024f27d3a1..88f3251b05e3 100644
--- a/kernel/extable.c
+++ b/kernel/extable.c
@@ -34,7 +34,8 @@ u32 __initdata __visible main_extable_sort_needed = 1;
 /* Sort the kernel's built-in exception table */
 void __init sort_main_extable(void)
 {
-	if (main_extable_sort_needed && __stop___ex_table > __start___ex_table) {
+	if (main_extable_sort_needed &&
+	    &__stop___ex_table > &__start___ex_table) {
 		pr_notice("Sorting __ex_table...\n");
 		sort_extable(__start___ex_table, __stop___ex_table);
 	}
-- 
2.25.1

Re: [PATCH v2] kernel/extable: Use address-of operator on section symbols

[Nathan Chancellor]

On Wed, Feb 19, 2020 at 01:20:37PM -0700, Nathan Chancellor wrote:
> Clang warns:
> 
> ../kernel/extable.c:37:52: warning: array comparison always evaluates to
> a constant [-Wtautological-compare]
>         if (main_extable_sort_needed && __stop___ex_table > __start___ex_table) {
>                                                           ^
> 1 warning generated.
> 
> These are not true arrays, they are linker defined symbols, which are
> just addresses. Using the address of operator silences the warning and
> does not change the resulting assembly with either clang/ld.lld or
> gcc/ld (tested with diff + objdump -Dr).
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/892
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>

Gah this should have:

Suggested-by: Nick Desaulniers <ndesaulniers@google.com>

I can send a v3 if necessary.

> ---
> 
> v1 -> v2: https://lore.kernel.org/lkml/20200219045423.54190-3-natechancellor@gmail.com/
> 
> * No longer a series because there is no prerequisite patch.
> * Use address-of operator instead of casting to unsigned long.
> 
>  kernel/extable.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/extable.c b/kernel/extable.c
> index a0024f27d3a1..88f3251b05e3 100644
> --- a/kernel/extable.c
> +++ b/kernel/extable.c
> @@ -34,7 +34,8 @@ u32 __initdata __visible main_extable_sort_needed = 1;
>  /* Sort the kernel's built-in exception table */
>  void __init sort_main_extable(void)
>  {
> -	if (main_extable_sort_needed && __stop___ex_table > __start___ex_table) {
> +	if (main_extable_sort_needed &&
> +	    &__stop___ex_table > &__start___ex_table) {
>  		pr_notice("Sorting __ex_table...\n");
>  		sort_extable(__start___ex_table, __stop___ex_table);
>  	}
> -- 
> 2.25.1
>