Re: [TESTING]: one more boot2 shrinking patch

On Thu, Mar 10, 2011 at 8:37 AM, Roman Divacky <rdivacky_at_freebsd.org> wrote:
> On Thu, Mar 10, 2011 at 09:20:58AM -0500, John Baldwin wrote:
>> On Wednesday, March 09, 2011 6:24:36 pm Dimitry Andric wrote:
>> > On 2011-03-09 14:23, John Baldwin wrote:
>> > >> gcc nor clang emits any code to initialize static type foo = 0;
>> > >> because it's expected that BSS is zeroed, which is not the case
>> > >> in boot2 so we have to initialize that explicitly
>> > > It used to be that if you explicitly initialized a variable to 0, it was
>> > > initialized to 0 in .data, but now gcc and clang recognize it is set to 0 and
>> > > move it to .bss.  There appears to be no way to turn this feature off,
>> >
>> > Yes, there is; both gcc and clang have this option to turn it off:
>> >
>> > -fno-zero-initialized-in-bss
>> >      If the target supports a BSS section, GCC by default puts variables
>> >      that are initialized to zero into BSS. This can save space in the
>> >      resulting code.
>> >
>> >      This option turns off this behavior because some programs
>> >      explicitly rely on variables going to the data section. E.g., so
>> >      that the resulting executable can find the beginning of that
>> >      section and/or make assumptions based on that.
>> >
>> >      The default is -fzero-initialized-in-bss.
>>
>> Hah, that is better then.  Thanks! I should have searched about this more
>> myself. :(  Roman, can you try reverting the kname changes and adding this
>> to CFLAGS instead for both compilers?
>
> when I put -fno-zero-initialized-in-bss clang does not fit by 1.7K and
> gcc by 0.5K, we dont want this :)

If there's that many variables explicitly initialized to zero, does
boot2 then need to explicitly bzero all of bss, not just kname, since
it's not handled by the loader?  Otherwise it sounds like either
there's a lot of explicitly initialized variables that didn't need to
be, or there's a lot of potential for uninitialized variable nonsense
to happen.

Thanks,
matthew