On 08/18/2017 08:01 AM, Richard Biener wrote:
> On Mon, Jul 31, 2017 at 7:35 AM, Jeff Law <l...@redhat.com> wrote:
>> This patch introduces the stack clash protection options
>>
>> Changes since V2:
>>
>> Adds two new params. The first controls the size of the guard area.
>> This controls the threshold for when a function prologue requires
>> probes. The second controls the probing interval -- ie, once probes are
>> needed, how often do we emit them. These are really meant more for
>> developers to experiment with than users. Regardless I did go ahead and
>> document them./PARAM
>>
>> It also adds some sanity checking WRT combining stack clash protection
>> with -fstack-check.
>
> diff --git a/gcc/params.c b/gcc/params.c
> index fab0ffa..8afe4c4 100644
> --- a/gcc/params.c
> +++ b/gcc/params.c
> @@ -209,6 +209,11 @@ set_param_value (const char *name, int value,
> error ("maximum value of parameter %qs is %u",
> compiler_params[i].option,
> compiler_params[i].max_value);
> + else if ((strcmp (name, "stack-clash-protection-guard-size") == 0
> + || strcmp (name, "stack-clash-protection-probe-interval") == 0)
> + && exact_log2 (value) == -1)
> + error ("value of parameter %qs must be a power of 2",
> + compiler_params[i].option);
> else
> set_param_value_internal ((compiler_param) i, value,
> params, params_set, true);
>
> I don't like this. Either use them as if they were power-of-two
> (floor_log2/ceil_log2 as appropriate) or simply make them take
> the logarithm instead (like -mincoming-stack-boundary and friends).
Yes. I was torn on this for a variety of reasons, including the fact
that I don't actually expect anyone to be mucking with those :-)
Given we've already other stuff in log2 form, I'll use that -- it seems
less surprising to me than using floor/ceil.
>
> Both -fstack-clash-protection and -fstack-check cannot be turned
> off per function. This means they would need merging in lto-wrapper.
> The alternative is to mark them with 'Optimization' and allow per-function
> specification (like we do for -fstack-protector).
Do you have a strong preference here? I'd tend to go with tweaking
lto-wrapper as we really don't want to have this stuff varying per-function.
Presumably in lto-wrapper we just have to detect that both were enabled
and do something sensible. We drop -fstack-check in toplev.c when both
are specified, we could just as easily call that situation a fatal error
in both toplev.c and lto-wrapper.c
jeff
