[PATCH v8 3/6] elf: Introduce _dl_map_segment_align hook for segment alignment tuning
H.J. Lu
hjl.tools@gmail.com
Tue Apr 7 00:38:14 GMT 2026
On Tue, Apr 7, 2026 at 7:09 AM H.J. Lu <hjl.tools@gmail.com> wrote:
>
> 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.
>
>
Here is the actual patch on top of yours to implement PT_LOAD
segment merging for THP:
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
0) = 0x55fe63888000
mmap(NULL, 4271952, PROT_NONE,
MAP_PRIVATE|MAP_ANONYMOUS|MAP_DENYWRITE, -1, 0) = 0x55fe63475000
mmap(0x55fe63600000, 2174800, PROT_READ|PROT_EXEC,
MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0) = 0x55fe63600000
mmap(0x55fe63800000, 24576, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x200000) = 0x55fe63800000
mmap(0x55fe63806000, 53072, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x55fe63806000
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
0) = 0x55fe63886000
mmap(NULL, 12, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0)
= 0x55fe63885000
vs
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
0) = 0x55d27fbd7000
mmap(NULL, 2174832, PROT_READ, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x55d27f800000
mmap(0x55d27f879000, 1601536, PROT_READ|PROT_EXEC,
MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x79000) = 0x55d27f879000
mmap(0x55d27fa00000, 24576, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x200000) = 0x55d27fa00000
mmap(0x55d27fa06000, 53104, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x55d27fa06000
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
0) = 0x55d27fbd5000
mmap(NULL, 12, PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, -1, 0)
= 0x55d27fbd4000
--
H.J.
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