Re: dynamic linker change to handle multiple PT_LOAD segments

[christos%astron.com@localhost (Christos Zoulas)]

In article <3CF2E88D-1262-419D-BFCF-C11599E2BE05%me.com@localhost>,
Jason Thorpe  <thorpej%me.com@localhost> wrote:
>
>> On Jan 5, 2023, at 8:53 AM, Christos Zoulas <christos%zoulas.com@localhost> wrote:
>> 
>> Hello,
>> 
>> Our dynamic linker ld_elf.so in map_object.c currently can only handle
>2 PT_LOAD segments (one for text and one for data); the kernel elf
>loader does not have this limitation, it can load multiple PT_LOAD
>segment. The following patch (from FreeBSD) removes this limitation from
>the dynamic linker. The reason I made this patch now is that the latest
>binutils (2.39) for amd64 sets a maxinum pagesize of 2Mb, and when using
>relocation read only binaries (ld -z relro) this will cause the binaries
>to have an extra 2Mbytes for alignment. This can be fixed by building
>binutils to set a separate code segment by default (ld -z
>separate-code). Binutils then sets the maximum page size to 4Kb. Setting
>this option creates 4 PT_LOAD segments, two for text (r--, r-x) and two
>for data (r--, rw-), which also improves security. This is the default
>for linux on x86 and the patch also makes it the default for NetBSD x86.
>The patch also adds -z noseparate-code to the kernel builds so that we
>don't need to fix the boot loaders. I am planning to commit this soon,
>so please let me know if you hsve any objections.
>> 
>> Best,
>> 
>> christos<separate-code.diff>
>
>Is this ld.elf_so change also going to be put into NetBSD 10?  (Seems
>like it could / should be?). That way, the configuration changes for the
>toolchain (which you will presumable want to upstream) can match against
>NetBSD 10 for the new defaults.

I've been mulling about it. I would like to give it enough time to be
tested on most platforms (ones that I don't have access to) first.

christos