Re: [PATCH bpf-next v3 3/4] x86: implement per-function metadata storage for x86

[Menglong Dong]

On Tue, Mar 4, 2025 at 10:07 AM Menglong Dong <menglong8.dong@xxxxxxxxx> wrote:
>
> On Tue, Mar 4, 2025 at 12:05 AM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
> >
> > On Mon,  3 Mar 2025 14:53:44 +0800
> > Menglong Dong <menglong8.dong@xxxxxxxxx> wrote:
> >
> > > In the third case, we make the kernel function 32 bytes aligned, and there
> > > will be 32 bytes padding before the functions. According to my testing,
> > > the text size didn't increase on this case, which is weird.
> > >
> > > With 16-bytes padding:
> > >
> > > -rwxr-xr-x 1 401190688  x86-dev/vmlinux*
> > > -rw-r--r-- 1    251068  x86-dev/vmlinux.a
> > > -rw-r--r-- 1 851892992  x86-dev/vmlinux.o
> > > -rw-r--r-- 1  12395008  x86-dev/arch/x86/boot/bzImage
> > >
> > > With 32-bytes padding:
> > >
> > > -rwxr-xr-x 1 401318128 x86-dev/vmlinux*
> > > -rw-r--r-- 1    251154 x86-dev/vmlinux.a
> > > -rw-r--r-- 1 853636704 x86-dev/vmlinux.o
> > > -rw-r--r-- 1  12509696 x86-dev/arch/x86/boot/bzImage
> >
> > Use the "size" command to see the differences in sizes and not the file size.
> >
> > $ size vmlinux
> >    text    data     bss     dec     hex filename
> > 36892658        9798658 16982016        63673332        3cb93f4 vmlinux
>
> Great! It seems that the way I tested has something wrong. I'll
> compare the text size with "size" command later.

With the size command, the text size with 32-bytes padding is:

  text    data     bss     dec     hex filename
48299471        14776173        18345936        81421580
4da650c x86-dev/vmlinux

And with 16-bytes padding is:

  text    data     bss     dec     hex filename
46620640        14772017        18458396        79851053
4c26e2d x86-dev/vmlinux

It increases about 3%, which I think is acceptable in this case.

I'll post the message in the commit log of the next version.

Thanks!
Menglong Dong

>
> Thanks!
> Menglong Dong
>
> >
> > -- Steve