[Bug ld/30907] ELF segment add extra 2 LOAD segments in aarch64, making binary bigger 128KiB than before

[nickc at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=30907

Nick Clifton <nickc at redhat dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |nickc at redhat dot com

--- Comment #2 from Nick Clifton <nickc at redhat dot com> ---
(In reply to nilus from comment #0)
Hi Nilus,

> When we use binutils 2.39 (or higher, like 2.40) to compile files on
> aarch64, we find that the newly compiled binary file size is 128K larger
> than the binary file compiled using binutils 2.38.

Are you concerned about disk space usage or memory usage ?

The larger version will probably not be occupying a lot more disk space, since
the unused sections of the file will not be allocated to real disk space. 
Likewise
the altered layout of the larger file will only matter to the runtime if they
cause extra pages to be allocated.


>   LOAD           0x0000000000000000 0x0000000000000000 0x0000000000000000
>                  0x0000000000003448 0x0000000000003448  R E    0x10000
>   LOAD           0x000000000000fc60 0x000000000001fc60 0x000000000001fc60
>                  0x00000000000003a8 0x00000000000003b0  RW     0x10000

>   Segment Sections...
>    00     .note.gnu.property .note.gnu.build-id .gnu.hash .dynsym .dynstr
> .gnu.version .gnu.version_r .rela.dyn .rela.plt .init .plt .text .fini
> .rodata .eh_frame_hdr .eh_frame 
>    01     .init_array .fini_array .dynamic .got .data .bss 

vs...

>   LOAD           0x0000000000000000 0x0000000000000000 0x0000000000000000
>                  0x0000000000001168 0x0000000000001168  R      0x10000
>   LOAD           0x0000000000010000 0x0000000000010000 0x0000000000010000
>                  0x0000000000001dc0 0x0000000000001dc0  R E    0x10000
>   LOAD           0x0000000000020000 0x0000000000020000 0x0000000000020000
>                  0x0000000000000a8c 0x0000000000000a8c  R      0x10000
>   LOAD           0x000000000002fc30 0x000000000003fc30 0x000000000003fc30
>                  0x00000000000003d8 0x00000000000003e0  RW     0x10000

>   Segment Sections...
>    00     .note.gnu.property .note.gnu.build-id .gnu.hash .dynsym .dynstr
> .gnu.version .gnu.version_r .rela.dyn .rela.plt 
>    01     .init .plt .text .fini 
>    02     .rodata .eh_frame_hdr .eh_frame 
>    03     .init_array .fini_array .dynamic .got .data .bss 

This is a security issue.  Notice how in the first version you have a segment
with Execute permission that contains lots of sections that do not need the
execution ability.  In the second version these sections are relegated to their
own, just read only, segment.  Likewise data is completely separated from code,
so the .rodata section for example no longer shares a segment with .text.

If you do not like this behaviour, you should be able to turn it off by linking
with "-z,noseparate-code".

Cheers
  Nick

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