Re: [PATCH 0/2] __builtin_unreachable

[AmÃrico Wang]

On Thu, Sep 10, 2009 at 9:59 AM, Roland McGrath <roland@xxxxxxxxxx> wrote:
> The latest GCC has a better way than "for (;;)" to indicate that a code
> path cannot be reached due to reasons the compiler doesn't understand (such
> as code in an asm). ÂThese patches provide UNREACHABLE() as a macro to hide
> the details of this, and then use it for the BUG() macro on x86, saving
> some dead code otherwise generated.
>
> Other arch's BUG() may want to this too instead of "for (;;)" or __builtin_trap.
>
> There are numerous matches from "git grep -n 'for *(;;) *;'" but it takes
> someone who knows each bit of code to know where that means UNREACHABLE()
> and where it really wants an infinite loop.

Looks good!

Reviewed-by: WANG Cong <xiyou.wangcong@xxxxxxxxx>

Just curious, what different asm code will gcc generate for this? Comparing it
to for(;;) ? I am sorry that I don't have gcc 4.5 on hand.

Thanks!
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/