diff mbox series

[v4] elf: Properly align PT_LOAD segments [BZ #28676]

Message ID YbJZDQzd0fcU0oxF@gmail.com
State Superseded
Headers show
Series [v4] elf: Properly align PT_LOAD segments [BZ #28676] | expand

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Context Check Description
dj/TryBot-apply_patch success Patch applied to master at the time it was sent
dj/TryBot-32bit success Build for i686

Commit Message

H.J. Lu Dec. 9, 2021, 7:29 p.m. UTC
On Thu, Dec 09, 2021 at 10:04:32AM -0800, H.J. Lu wrote:
> On Thu, Dec 09, 2021 at 07:14:10AM -0800, H.J. Lu wrote:
> 
> Hi,
> 
> I updated your patch.  Please take a look.
> 
> 
> H.J.
> --
> When PT_LOAD segment alignment > the page size, allocate enough space
> to ensure that the segment can be properly aligned.
> 
> This fixes [BZ #28676].


H.J.
---
Changes in v4:

1. Call unmap when the second mmap fails.

When PT_LOAD segment alignment > the page size, allocate enough space
to ensure that the segment can be properly aligned.

This fixes [BZ #28676].
---
 elf/dl-load.c         |  1 +
 elf/dl-load.h         |  2 +-
 elf/dl-map-segments.h | 49 +++++++++++++++++++++++++++++++++++++++----
 3 files changed, 47 insertions(+), 5 deletions(-)

Comments

Rongwei Wang Dec. 10, 2021, 1:58 a.m. UTC | #1
Hi, lhj

Thanks for your help! It's much better than my version.
And I find a small bug. you can check it again if available.

On 12/10/21 3:29 AM, H.J. Lu wrote:
> On Thu, Dec 09, 2021 at 10:04:32AM -0800, H.J. Lu wrote:
>> On Thu, Dec 09, 2021 at 07:14:10AM -0800, H.J. Lu wrote:
>>
>> Hi,
>>
>> I updated your patch.  Please take a look.
>>
>>
>> H.J.
>> --
>> When PT_LOAD segment alignment > the page size, allocate enough space
>> to ensure that the segment can be properly aligned.
>>
>> This fixes [BZ #28676].
> 
> 
> H.J.
> ---
> Changes in v4:
> 
> 1. Call unmap when the second mmap fails.
> 
> When PT_LOAD segment alignment > the page size, allocate enough space
> to ensure that the segment can be properly aligned.
> 
> This fixes [BZ #28676].
> ---
>   elf/dl-load.c         |  1 +
>   elf/dl-load.h         |  2 +-
>   elf/dl-map-segments.h | 49 +++++++++++++++++++++++++++++++++++++++----
>   3 files changed, 47 insertions(+), 5 deletions(-)
> 
> diff --git a/elf/dl-load.c b/elf/dl-load.c
> index bf8957e73c..9a23590bf4 100644
> --- a/elf/dl-load.c
> +++ b/elf/dl-load.c
> @@ -1150,6 +1150,7 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
>   	  c->mapend = ALIGN_UP (ph->p_vaddr + ph->p_filesz, GLRO(dl_pagesize));
>   	  c->dataend = ph->p_vaddr + ph->p_filesz;
>   	  c->allocend = ph->p_vaddr + ph->p_memsz;
> +	  c->mapalign = ph->p_align;
>   	  c->mapoff = ALIGN_DOWN (ph->p_offset, GLRO(dl_pagesize));
>   
>   	  /* Determine whether there is a gap between the last segment
> diff --git a/elf/dl-load.h b/elf/dl-load.h
> index e329d49a81..c121e3456c 100644
> --- a/elf/dl-load.h
> +++ b/elf/dl-load.h
> @@ -74,7 +74,7 @@ ELF_PREFERRED_ADDRESS_DATA;
>      Its details have been expanded out and converted.  */
>   struct loadcmd
>   {
> -  ElfW(Addr) mapstart, mapend, dataend, allocend;
> +  ElfW(Addr) mapstart, mapend, dataend, allocend, mapalign;
>     ElfW(Off) mapoff;
>     int prot;                             /* PROT_* bits.  */
>   };
> diff --git a/elf/dl-map-segments.h b/elf/dl-map-segments.h
> index f9fb110ee3..f710cf2e48 100644
> --- a/elf/dl-map-segments.h
> +++ b/elf/dl-map-segments.h
> @@ -18,6 +18,50 @@
>   
>   #include <dl-load.h>
>   
> +/* Map a segment and align it properly.  */
> +
> +static __always_inline ElfW(Addr)
> +_dl_map_segment (const struct loadcmd *c, ElfW(Addr) mappref,
> +		 const size_t maplength, int fd)
> +{
> +  if (__glibc_likely (c->mapalign <= GLRO(dl_pagesize)))
> +    return (ElfW(Addr)) __mmap ((void *) mappref, maplength, c->prot,
> +				MAP_COPY|MAP_FILE, fd, c->mapoff);
> +
> +  /* If the segment alignment > the page size, allocate enough space to
> +     ensure that the segment can be properly aligned.  */
> +  ElfW(Addr) maplen = (maplength >= c->mapalign
> +		       ? (maplength + c->mapalign)
> +		       : (2 * c->mapalign));
> +  ElfW(Addr) map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplen,
> +					      PROT_NONE,
> +					      MAP_ANONYMOUS|MAP_PRIVATE,
> +					      -1, 0);
> +  if (__glibc_unlikely ((void *) map_start == MAP_FAILED))
> +    return map_start;
> +
> +  ElfW(Addr) map_start_aligned = ALIGN_UP (map_start, c->mapalign);
> +  map_start_aligned = (ElfW(Addr)) __mmap ((void *) map_start_aligned,
> +					   maplength, c->prot,
> +					   MAP_COPY|MAP_FILE|MAP_FIXED,
> +					   fd, c->mapoff);
> +  if (__glibc_unlikely ((void *) map_start == MAP_FAILED))
Is map_start_aligned here?

> +    __munmap ((void *) map_start, maplen);
> +  else
> +    {
> +      /* Unmap the unused regions.  */
> +      ElfW(Addr) delta = map_start_aligned - map_start;
> +      if (delta)
> +	__munmap ((void *) map_start, delta);
> +      ElfW(Addr) map_end = map_start_aligned + maplength;
> +      delta = map_start + maplen - map_end;
> +      if (delta)
> +	__munmap ((void *) map_end, delta);
> +    }
> +
> +  return map_start_aligned;
> +}
> +
>   /* This implementation assumes (as does the corresponding implementation
>      of _dl_unmap_segments, in dl-unmap-segments.h) that shared objects
>      are always laid out with all segments contiguous (or with gaps
> @@ -53,10 +97,7 @@ _dl_map_segments (struct link_map *l, int fd,
>              - MAP_BASE_ADDR (l));
>   
>         /* Remember which part of the address space this object uses.  */
> -      l->l_map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplength,
> -                                            c->prot,
> -                                            MAP_COPY|MAP_FILE,
> -                                            fd, c->mapoff);
> +      l->l_map_start = _dl_map_segment (c, mappref, maplength, fd);
>         if (__glibc_unlikely ((void *) l->l_map_start == MAP_FAILED))
>           return DL_MAP_SEGMENTS_ERROR_MAP_SEGMENT;
>   
> 
All is OK for me.

And I am not sure whether I need to add a testcase in one new patch, 
because I saw you had submitted the testcase: 
https://gitlab.com/x86-glibc/glibc/-/commit/ba63c1cb2ea1b0ae421f66756771ff4c89d4a470

I will test it again, and send out PATCH v5.

Thanks.
H.J. Lu Dec. 10, 2021, 2:24 a.m. UTC | #2
On Thu, Dec 9, 2021 at 5:58 PM Rongwei Wang
<rongwei.wang@linux.alibaba.com> wrote:
>
>
> Hi, lhj
>
> Thanks for your help! It's much better than my version.
> And I find a small bug. you can check it again if available.
>
> On 12/10/21 3:29 AM, H.J. Lu wrote:
> > On Thu, Dec 09, 2021 at 10:04:32AM -0800, H.J. Lu wrote:
> >> On Thu, Dec 09, 2021 at 07:14:10AM -0800, H.J. Lu wrote:
> >>
> >> Hi,
> >>
> >> I updated your patch.  Please take a look.
> >>
> >>
> >> H.J.
> >> --
> >> When PT_LOAD segment alignment > the page size, allocate enough space
> >> to ensure that the segment can be properly aligned.
> >>
> >> This fixes [BZ #28676].
> >
> >
> > H.J.
> > ---
> > Changes in v4:
> >
> > 1. Call unmap when the second mmap fails.
> >
> > When PT_LOAD segment alignment > the page size, allocate enough space
> > to ensure that the segment can be properly aligned.
> >
> > This fixes [BZ #28676].
> > ---
> >   elf/dl-load.c         |  1 +
> >   elf/dl-load.h         |  2 +-
> >   elf/dl-map-segments.h | 49 +++++++++++++++++++++++++++++++++++++++----
> >   3 files changed, 47 insertions(+), 5 deletions(-)
> >
> > diff --git a/elf/dl-load.c b/elf/dl-load.c
> > index bf8957e73c..9a23590bf4 100644
> > --- a/elf/dl-load.c
> > +++ b/elf/dl-load.c
> > @@ -1150,6 +1150,7 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
> >         c->mapend = ALIGN_UP (ph->p_vaddr + ph->p_filesz, GLRO(dl_pagesize));
> >         c->dataend = ph->p_vaddr + ph->p_filesz;
> >         c->allocend = ph->p_vaddr + ph->p_memsz;
> > +       c->mapalign = ph->p_align;
> >         c->mapoff = ALIGN_DOWN (ph->p_offset, GLRO(dl_pagesize));
> >
> >         /* Determine whether there is a gap between the last segment
> > diff --git a/elf/dl-load.h b/elf/dl-load.h
> > index e329d49a81..c121e3456c 100644
> > --- a/elf/dl-load.h
> > +++ b/elf/dl-load.h
> > @@ -74,7 +74,7 @@ ELF_PREFERRED_ADDRESS_DATA;
> >      Its details have been expanded out and converted.  */
> >   struct loadcmd
> >   {
> > -  ElfW(Addr) mapstart, mapend, dataend, allocend;
> > +  ElfW(Addr) mapstart, mapend, dataend, allocend, mapalign;
> >     ElfW(Off) mapoff;
> >     int prot;                             /* PROT_* bits.  */
> >   };
> > diff --git a/elf/dl-map-segments.h b/elf/dl-map-segments.h
> > index f9fb110ee3..f710cf2e48 100644
> > --- a/elf/dl-map-segments.h
> > +++ b/elf/dl-map-segments.h
> > @@ -18,6 +18,50 @@
> >
> >   #include <dl-load.h>
> >
> > +/* Map a segment and align it properly.  */
> > +
> > +static __always_inline ElfW(Addr)
> > +_dl_map_segment (const struct loadcmd *c, ElfW(Addr) mappref,
> > +              const size_t maplength, int fd)
> > +{
> > +  if (__glibc_likely (c->mapalign <= GLRO(dl_pagesize)))
> > +    return (ElfW(Addr)) __mmap ((void *) mappref, maplength, c->prot,
> > +                             MAP_COPY|MAP_FILE, fd, c->mapoff);
> > +
> > +  /* If the segment alignment > the page size, allocate enough space to
> > +     ensure that the segment can be properly aligned.  */
> > +  ElfW(Addr) maplen = (maplength >= c->mapalign
> > +                    ? (maplength + c->mapalign)
> > +                    : (2 * c->mapalign));
> > +  ElfW(Addr) map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplen,
> > +                                           PROT_NONE,
> > +                                           MAP_ANONYMOUS|MAP_PRIVATE,
> > +                                           -1, 0);
> > +  if (__glibc_unlikely ((void *) map_start == MAP_FAILED))
> > +    return map_start;
> > +
> > +  ElfW(Addr) map_start_aligned = ALIGN_UP (map_start, c->mapalign);
> > +  map_start_aligned = (ElfW(Addr)) __mmap ((void *) map_start_aligned,
> > +                                        maplength, c->prot,
> > +                                        MAP_COPY|MAP_FILE|MAP_FIXED,
> > +                                        fd, c->mapoff);
> > +  if (__glibc_unlikely ((void *) map_start == MAP_FAILED))
> Is map_start_aligned here?
>
> > +    __munmap ((void *) map_start, maplen);
> > +  else
> > +    {
> > +      /* Unmap the unused regions.  */
> > +      ElfW(Addr) delta = map_start_aligned - map_start;
> > +      if (delta)
> > +     __munmap ((void *) map_start, delta);
> > +      ElfW(Addr) map_end = map_start_aligned + maplength;
> > +      delta = map_start + maplen - map_end;
> > +      if (delta)
> > +     __munmap ((void *) map_end, delta);
> > +    }
> > +
> > +  return map_start_aligned;
> > +}
> > +
> >   /* This implementation assumes (as does the corresponding implementation
> >      of _dl_unmap_segments, in dl-unmap-segments.h) that shared objects
> >      are always laid out with all segments contiguous (or with gaps
> > @@ -53,10 +97,7 @@ _dl_map_segments (struct link_map *l, int fd,
> >              - MAP_BASE_ADDR (l));
> >
> >         /* Remember which part of the address space this object uses.  */
> > -      l->l_map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplength,
> > -                                            c->prot,
> > -                                            MAP_COPY|MAP_FILE,
> > -                                            fd, c->mapoff);
> > +      l->l_map_start = _dl_map_segment (c, mappref, maplength, fd);
> >         if (__glibc_unlikely ((void *) l->l_map_start == MAP_FAILED))
> >           return DL_MAP_SEGMENTS_ERROR_MAP_SEGMENT;
> >
> >
> All is OK for me.
>
> And I am not sure whether I need to add a testcase in one new patch,
> because I saw you had submitted the testcase:
> https://gitlab.com/x86-glibc/glibc/-/commit/ba63c1cb2ea1b0ae421f66756771ff4c89d4a470

No, I didn't submit it.

> I will test it again, and send out PATCH v5.

Please include my testcase in your v5 patch.

Thanks.


--
H.J.
Rongwei Wang Dec. 10, 2021, 2:34 a.m. UTC | #3
On 12/10/21 10:24 AM, H.J. Lu wrote:
> On Thu, Dec 9, 2021 at 5:58 PM Rongwei Wang
> <rongwei.wang@linux.alibaba.com> wrote:
>>
>>
>> Hi, lhj
>>
>> Thanks for your help! It's much better than my version.
>> And I find a small bug. you can check it again if available.
>>
>> On 12/10/21 3:29 AM, H.J. Lu wrote:
>>> On Thu, Dec 09, 2021 at 10:04:32AM -0800, H.J. Lu wrote:
>>>> On Thu, Dec 09, 2021 at 07:14:10AM -0800, H.J. Lu wrote:
>>>>
>>>> Hi,
>>>>
>>>> I updated your patch.  Please take a look.
>>>>
>>>>
>>>> H.J.
>>>> --
>>>> When PT_LOAD segment alignment > the page size, allocate enough space
>>>> to ensure that the segment can be properly aligned.
>>>>
>>>> This fixes [BZ #28676].
>>>
>>>
>>> H.J.
>>> ---
>>> Changes in v4:
>>>
>>> 1. Call unmap when the second mmap fails.
>>>
>>> When PT_LOAD segment alignment > the page size, allocate enough space
>>> to ensure that the segment can be properly aligned.
>>>
>>> This fixes [BZ #28676].
>>> ---
>>>    elf/dl-load.c         |  1 +
>>>    elf/dl-load.h         |  2 +-
>>>    elf/dl-map-segments.h | 49 +++++++++++++++++++++++++++++++++++++++----
>>>    3 files changed, 47 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/elf/dl-load.c b/elf/dl-load.c
>>> index bf8957e73c..9a23590bf4 100644
>>> --- a/elf/dl-load.c
>>> +++ b/elf/dl-load.c
>>> @@ -1150,6 +1150,7 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
>>>          c->mapend = ALIGN_UP (ph->p_vaddr + ph->p_filesz, GLRO(dl_pagesize));
>>>          c->dataend = ph->p_vaddr + ph->p_filesz;
>>>          c->allocend = ph->p_vaddr + ph->p_memsz;
>>> +       c->mapalign = ph->p_align;
>>>          c->mapoff = ALIGN_DOWN (ph->p_offset, GLRO(dl_pagesize));
>>>
>>>          /* Determine whether there is a gap between the last segment
>>> diff --git a/elf/dl-load.h b/elf/dl-load.h
>>> index e329d49a81..c121e3456c 100644
>>> --- a/elf/dl-load.h
>>> +++ b/elf/dl-load.h
>>> @@ -74,7 +74,7 @@ ELF_PREFERRED_ADDRESS_DATA;
>>>       Its details have been expanded out and converted.  */
>>>    struct loadcmd
>>>    {
>>> -  ElfW(Addr) mapstart, mapend, dataend, allocend;
>>> +  ElfW(Addr) mapstart, mapend, dataend, allocend, mapalign;
>>>      ElfW(Off) mapoff;
>>>      int prot;                             /* PROT_* bits.  */
>>>    };
>>> diff --git a/elf/dl-map-segments.h b/elf/dl-map-segments.h
>>> index f9fb110ee3..f710cf2e48 100644
>>> --- a/elf/dl-map-segments.h
>>> +++ b/elf/dl-map-segments.h
>>> @@ -18,6 +18,50 @@
>>>
>>>    #include <dl-load.h>
>>>
>>> +/* Map a segment and align it properly.  */
>>> +
>>> +static __always_inline ElfW(Addr)
>>> +_dl_map_segment (const struct loadcmd *c, ElfW(Addr) mappref,
>>> +              const size_t maplength, int fd)
>>> +{
>>> +  if (__glibc_likely (c->mapalign <= GLRO(dl_pagesize)))
>>> +    return (ElfW(Addr)) __mmap ((void *) mappref, maplength, c->prot,
>>> +                             MAP_COPY|MAP_FILE, fd, c->mapoff);
>>> +
>>> +  /* If the segment alignment > the page size, allocate enough space to
>>> +     ensure that the segment can be properly aligned.  */
>>> +  ElfW(Addr) maplen = (maplength >= c->mapalign
>>> +                    ? (maplength + c->mapalign)
>>> +                    : (2 * c->mapalign));
>>> +  ElfW(Addr) map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplen,
>>> +                                           PROT_NONE,
>>> +                                           MAP_ANONYMOUS|MAP_PRIVATE,
>>> +                                           -1, 0);
>>> +  if (__glibc_unlikely ((void *) map_start == MAP_FAILED))
>>> +    return map_start;
>>> +
>>> +  ElfW(Addr) map_start_aligned = ALIGN_UP (map_start, c->mapalign);
>>> +  map_start_aligned = (ElfW(Addr)) __mmap ((void *) map_start_aligned,
>>> +                                        maplength, c->prot,
>>> +                                        MAP_COPY|MAP_FILE|MAP_FIXED,
>>> +                                        fd, c->mapoff);
>>> +  if (__glibc_unlikely ((void *) map_start == MAP_FAILED))
>> Is map_start_aligned here?
>>
>>> +    __munmap ((void *) map_start, maplen);
>>> +  else
>>> +    {
>>> +      /* Unmap the unused regions.  */
>>> +      ElfW(Addr) delta = map_start_aligned - map_start;
>>> +      if (delta)
>>> +     __munmap ((void *) map_start, delta);
>>> +      ElfW(Addr) map_end = map_start_aligned + maplength;
>>> +      delta = map_start + maplen - map_end;
>>> +      if (delta)
>>> +     __munmap ((void *) map_end, delta);
>>> +    }
>>> +
>>> +  return map_start_aligned;
>>> +}
>>> +
>>>    /* This implementation assumes (as does the corresponding implementation
>>>       of _dl_unmap_segments, in dl-unmap-segments.h) that shared objects
>>>       are always laid out with all segments contiguous (or with gaps
>>> @@ -53,10 +97,7 @@ _dl_map_segments (struct link_map *l, int fd,
>>>               - MAP_BASE_ADDR (l));
>>>
>>>          /* Remember which part of the address space this object uses.  */
>>> -      l->l_map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplength,
>>> -                                            c->prot,
>>> -                                            MAP_COPY|MAP_FILE,
>>> -                                            fd, c->mapoff);
>>> +      l->l_map_start = _dl_map_segment (c, mappref, maplength, fd);
>>>          if (__glibc_unlikely ((void *) l->l_map_start == MAP_FAILED))
>>>            return DL_MAP_SEGMENTS_ERROR_MAP_SEGMENT;
>>>
>>>
>> All is OK for me.
>>
>> And I am not sure whether I need to add a testcase in one new patch,
>> because I saw you had submitted the testcase:
>> https://gitlab.com/x86-glibc/glibc/-/commit/ba63c1cb2ea1b0ae421f66756771ff4c89d4a470
> 
> No, I didn't submit it.
> 
>> I will test it again, and send out PATCH v5.
> 
> Please include my testcase in your v5 patch.
Ok

Thanks.

> 
> Thanks.
> 
> 
> --
> H.J.
>
diff mbox series

Patch

diff --git a/elf/dl-load.c b/elf/dl-load.c
index bf8957e73c..9a23590bf4 100644
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -1150,6 +1150,7 @@  _dl_map_object_from_fd (const char *name, const char *origname, int fd,
 	  c->mapend = ALIGN_UP (ph->p_vaddr + ph->p_filesz, GLRO(dl_pagesize));
 	  c->dataend = ph->p_vaddr + ph->p_filesz;
 	  c->allocend = ph->p_vaddr + ph->p_memsz;
+	  c->mapalign = ph->p_align;
 	  c->mapoff = ALIGN_DOWN (ph->p_offset, GLRO(dl_pagesize));
 
 	  /* Determine whether there is a gap between the last segment
diff --git a/elf/dl-load.h b/elf/dl-load.h
index e329d49a81..c121e3456c 100644
--- a/elf/dl-load.h
+++ b/elf/dl-load.h
@@ -74,7 +74,7 @@  ELF_PREFERRED_ADDRESS_DATA;
    Its details have been expanded out and converted.  */
 struct loadcmd
 {
-  ElfW(Addr) mapstart, mapend, dataend, allocend;
+  ElfW(Addr) mapstart, mapend, dataend, allocend, mapalign;
   ElfW(Off) mapoff;
   int prot;                             /* PROT_* bits.  */
 };
diff --git a/elf/dl-map-segments.h b/elf/dl-map-segments.h
index f9fb110ee3..f710cf2e48 100644
--- a/elf/dl-map-segments.h
+++ b/elf/dl-map-segments.h
@@ -18,6 +18,50 @@ 
 
 #include <dl-load.h>
 
+/* Map a segment and align it properly.  */
+
+static __always_inline ElfW(Addr)
+_dl_map_segment (const struct loadcmd *c, ElfW(Addr) mappref,
+		 const size_t maplength, int fd)
+{
+  if (__glibc_likely (c->mapalign <= GLRO(dl_pagesize)))
+    return (ElfW(Addr)) __mmap ((void *) mappref, maplength, c->prot,
+				MAP_COPY|MAP_FILE, fd, c->mapoff);
+
+  /* If the segment alignment > the page size, allocate enough space to
+     ensure that the segment can be properly aligned.  */
+  ElfW(Addr) maplen = (maplength >= c->mapalign
+		       ? (maplength + c->mapalign)
+		       : (2 * c->mapalign));
+  ElfW(Addr) map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplen,
+					      PROT_NONE,
+					      MAP_ANONYMOUS|MAP_PRIVATE,
+					      -1, 0);
+  if (__glibc_unlikely ((void *) map_start == MAP_FAILED))
+    return map_start;
+
+  ElfW(Addr) map_start_aligned = ALIGN_UP (map_start, c->mapalign);
+  map_start_aligned = (ElfW(Addr)) __mmap ((void *) map_start_aligned,
+					   maplength, c->prot,
+					   MAP_COPY|MAP_FILE|MAP_FIXED,
+					   fd, c->mapoff);
+  if (__glibc_unlikely ((void *) map_start == MAP_FAILED))
+    __munmap ((void *) map_start, maplen);
+  else
+    {
+      /* Unmap the unused regions.  */
+      ElfW(Addr) delta = map_start_aligned - map_start;
+      if (delta)
+	__munmap ((void *) map_start, delta);
+      ElfW(Addr) map_end = map_start_aligned + maplength;
+      delta = map_start + maplen - map_end;
+      if (delta)
+	__munmap ((void *) map_end, delta);
+    }
+
+  return map_start_aligned;
+}
+
 /* This implementation assumes (as does the corresponding implementation
    of _dl_unmap_segments, in dl-unmap-segments.h) that shared objects
    are always laid out with all segments contiguous (or with gaps
@@ -53,10 +97,7 @@  _dl_map_segments (struct link_map *l, int fd,
            - MAP_BASE_ADDR (l));
 
       /* Remember which part of the address space this object uses.  */
-      l->l_map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplength,
-                                            c->prot,
-                                            MAP_COPY|MAP_FILE,
-                                            fd, c->mapoff);
+      l->l_map_start = _dl_map_segment (c, mappref, maplength, fd);
       if (__glibc_unlikely ((void *) l->l_map_start == MAP_FAILED))
         return DL_MAP_SEGMENTS_ERROR_MAP_SEGMENT;