[PATCH] ld: Disable separate code by default for Linux/x86

[hev]

On Tue, Mar 17, 2026 at 5:47 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> > One benefit of -z noseparate-code is that the executable PT_LOAD ends
> > up at virtual address 0 with file offset 0. For huge page mappings,
> > both the virtual address and the file offset need to be aligned to the
> > huge page size, e.g.
> >
> > ((p_vaddr | p_offset) & (HUGE_PAGE_SIZE - 1)) == 0
> >
> > Are you suggesting that, with the -z separate-code layout, ld.so would
> > ignore the non-executable flag of the first PT_LOAD and merge it with
> > the second PT_LOAD, mapping them together as read-only executable?
> > That might help with existing binaries, but wouldn't it blur the
> > permission boundaries between segments?
> >
>
> That is correct.  It should have the similar effect as -z noseparate-code.
> The difference is link-time vs run-time.  Of course, ld.so should do it only
> when huge page is in use.

Having ld.so transparently merge the mappings doesn't always seem
workable. For example, in chromium the RE segment has different
virtual addresses and file offsets, so we can't construct a correct
mapping when attempting to merge them.

  LOAD           0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x00000000014d2b2c 0x00000000014d2b2c  R      0x1000
  LOAD           0x00000000014d3000 0x00000000014d4000 0x00000000014d4000
                 0x000000000fb7a420 0x000000000fb7a420  R E    0x1000
  LOAD           0x000000001104d420 0x000000001104f420 0x000000001104f420
                 0x0000000000ac0f58 0x0000000000ac1be0  RW     0x1000
  LOAD           0x0000000011b0f000 0x0000000011b12000 0x0000000011b12000
                 0x0000000000146001 0x0000000000428d34  RW     0x1000

Thanks,
Rui