[PATCH] ld: Avoid moving desired relro end below relro section

[H.J. Lu]

On Sun, Feb 16, 2025 at 12:38 PM Alan Modra <amodra@gmail.com> wrote:
>
> On Sun, Feb 16, 2025 at 06:19:07AM +0800, H.J. Lu wrote:
> > --- a/ld/ldlang.c
> > +++ b/ld/ldlang.c
> > @@ -6605,10 +6605,16 @@ lang_size_relro_segment_1 (void)
> >       end = start = sec->vma;
> >       if (!IS_TBSS (sec))
> >         end += TO_ADDR (sec->size);
> > -     bump = desired_end - end;
> > -     /* We'd like to increase START by BUMP, but we must heed
> > -        alignment so the increase might be less than optimum.  */
> > -     start += bump;
> > +     if (desired_end > end)
> > +       {
> > +         /* Avoid moving START backwards.  */
> > +         bump = desired_end - end;
> > +         /* We'd like to increase START by BUMP, but we must heed
> > +            alignment so the increase might be less than optimum.  */
> > +         start += bump;
> > +       }
> > +     else
> > +       start = end;
> >       start &= ~(((bfd_vma) 1 << sec->alignment_power) - 1);
> >       /* This is now the desired end for the previous section.  */
> >       desired_end = start;
>
> This doesn't make any sense at all.  You're putting sections on top of
> each other!
>
> The assert failure can't be fixed by totally breaking this function.
>
> Look instead at why sections now don't fit.  Have they changed in size
> since the time seg->relro_end and seg->base were set?

When setting seg->base to 0x2f3000, there are:

section       vma           size      vma + size    alignment
.got   0x2c2118   0x0    0x2c2118   8
.dynamic   0x2c20e8   0x0    0x2c20e8   8
.data.rel.ro   0x298020   0x0    0x298020   32
.fini_array   0x298008   0x0    0x298008   8
.init_array   0x298000   0x0    0x298000   8

When setting seg->relro_end to 0x320fe8 after that, there are

section       vma           size      vma + size    alignment
.got   0x320268   0xd80    0x320fe8   8
.dynamic   0x31ffe8   0x280    0x320268   8
.data.rel.ro   0x2f3020   0x2cfc8    0x31ffe8   128
.fini_array   0x2f3008   0x8    0x2f3010   8
.init_array   0x2f3000   0x8    0x2f3008   8

All section sizes are 0 when setting seg->base.

-- 
H.J.