> On 22 Apr 2020, at 15:35, Andi Kleen <ak@xxxxxxxxxxxxxxx> wrote:
>
>
> Thanks good catch.
>
>> if (cmdline_find_option(boot_command_line, "clearcpuid", arg,
>> - sizeof(arg)) &&
>> - get_option(&argptr, &bit) &&
>> - bit >= 0 &&
>> - bit < NCAPINTS * 32)
>> - setup_clear_cpu_cap(bit);
>> + sizeof(arg))) {
>> + /* cpuid bit numbers are mostly three digits */
>> + enum { nints = sizeof(arg)/(3+1) + 1 };
>
> Not sure what the digits have to do with the stack space of an int array.
>
> We should have enough stack to afford some more than 8.
sizeof(arg) == 32; room enough for eight three-digit with their trailing commas. If sizeof(arg) == 1024 instead then there'd be more than enough room to remove every single feature. TBH, 512 is more than enough for the 89 flags I have listed on this machine I'm looking at here. I'll grow sizeof(arg) and nints accordingly.
>
> Would be good to have a warning if the arguments are longer.
>
Yes, I should definitely do that -- coming to a V2 soon.
> Maybe it would be simpler to fix the early arg parser
> to allow multiple instances again? That would also avoid the limit,
> and keep everything compatible.
>
I did wonder about that. However, cmdline_find_option() is specifically documented as
* Find a non-boolean option (i.e. option=argument). In accordance with
* standard Linux practice, if this option is repeated, this returns the
* last instance on the command line.
And since that appeared in 2017 I decided to stick with the new-fangled interface :) This is a little-used feature; I'm not sure it's worth the effort of parsing the command line for the old style. What do you think?
jch
> -Andi
>
>
>> + int i, bits[nints];
>> +
>> + get_options(arg, nints, bits);
>> + for (i = 1; i <= bits[0]; i++) {
>> + if (bits[i] >= 0 && bits[i] < NCAPINTS * 32)
>> + setup_clear_cpu_cap(bits[i]);
>> + }
>> + }
>> }
>>
>> /*
>> --
>> 2.25.3
>>
