[PATCH v8 3/6] elf: Introduce _dl_map_segment_align hook for segment alignment tuning

[H.J. Lu]

On Tue, Apr 7, 2026 at 6:56 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> On Mon, Apr 6, 2026 at 4:02 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> >
> > On Sun, Apr 5, 2026 at 11:54 AM WANG Rui <wangrui@loongson.cn> wrote:
> > >
> > > Introduce a new helper function, _dl_map_segment_align, to allow
> > > architecture-specific adjustment of ELF load segment alignment during
> > > object mapping.
> > >
> > > The generic ELF loader now calls this hook when determining the maximum
> > > segment alignment.  The generic implementation is a no-op and preserves
> > > existing behavior.
> > >
> > > This provides a well-defined extension point for architectures that
> > > need to adjust segment alignment policies (for example, to improve
> > > mapping efficiency or enable platform-specific optimizations) without
> > > embedding such logic directly in the generic loader.
> > >
> > > Reviewed-by: Wilco Dijkstra  <Wilco.Dijkstra@arm.com>
> > > Signed-off-by: WANG Rui <wangrui@loongson.cn>
> > > ---
> > >  elf/dl-load.c                          |  4 ++++
> > >  sysdeps/generic/dl-map-segment-align.h | 26 ++++++++++++++++++++++++++
> > >  2 files changed, 30 insertions(+)
> > >  create mode 100644 sysdeps/generic/dl-map-segment-align.h
> > >
> > > diff --git a/elf/dl-load.c b/elf/dl-load.c
> > > index 7355eef8e76..f3d943e99c0 100644
> > > --- a/elf/dl-load.c
> > > +++ b/elf/dl-load.c
> > > @@ -71,6 +71,7 @@ struct filebuf
> > >  #include <dl-dst.h>
> > >  #include <dl-load.h>
> > >  #include <dl-map-segments.h>
> > > +#include <dl-map-segment-align.h>
> > >  #include <dl-unmap-segments.h>
> > >  #include <dl-machine-reject-phdr.h>
> > >  #include <dl-prop.h>
> > > @@ -1171,6 +1172,9 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
> > >
> > >           /* Optimize a common case.  */
> > >           c->prot = pf_to_prot (ph->p_flags);
> > > +
> > > +         /* Architecture-specific adjustment of segment alignment. */
> > > +         p_align_max = _dl_map_segment_align (c, p_align_max);
> > >           break;
> >
> > Can you make THP to work for
> >
> > Program Headers:
> >   Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg Align
> >   PHDR           0x000034 0x00400034 0x00400034 0x001a0 0x001a0 R   0x4
> >   INTERP         0x0001f8 0x004001f8 0x004001f8 0x0001a 0x0001a R   0x1
> >       [Requesting program interpreter: /libx32/ld-linux-x32.so.2]
> >   LOAD           0x000000 0x00400000 0x00400000 0x16d110 0x16d110 R   0x1000
> >   LOAD           0x16e000 0x0056e000 0x0056e000 0x1055d9 0x1055d9 R E 0x1000
> >   LOAD           0x273ebc 0x00674ebc 0x00674ebc 0x02540 0x039fc RW  0x1000
> >   DYNAMIC        0x273ec8 0x00674ec8 0x00674ec8 0x00110 0x00110 RW  0x4
> >   NOTE           0x0001d4 0x004001d4 0x004001d4 0x00024 0x00024 R   0x4
> >   NOTE           0x16d0b0 0x0056d0b0 0x0056d0b0 0x00060 0x00060 R   0x4
> >   TLS            0x273ebc 0x00674ebc 0x00674ebc 0x00000 0x0000c R   0x4
> >   GNU_PROPERTY   0x16d0b0 0x0056d0b0 0x0056d0b0 0x00040 0x00040 R   0x4
> >   GNU_EH_FRAME   0x1493e0 0x005493e0 0x005493e0 0x05b94 0x05b94 R   0x4
> >   GNU_STACK      0x000000 0x00000000 0x00000000 0x00000 0x00000 RW  0x10
> >   GNU_RELRO      0x273ebc 0x00674ebc 0x00674ebc 0x00144 0x00144 R   0x1
> >
> > As an option, we can combine
> >
> >   LOAD           0x000000 0x00400000 0x00400000 0x16d110 0x16d110 R   0x1000
> >   LOAD           0x16e000 0x0056e000 0x0056e000 0x1055d9 0x1055d9 R E 0x1000
> >
> > into a single RE THP map.
> >
>
> Something like this.
>
>
> --
> H.J.

A better _dl_map_segment_adjust hook.

-- 
H.J.
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