Re: dynamic linker change to handle multiple PT_LOAD segments

[Jason Thorpe <thorpej%me.com@localhost>]

> 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.

-- thorpej