On Fri, Nov 05, 2021 at 10:42:05AM +0100, Richard Biener via Gcc-patches wrote:
> I had the impression we have support for PCH file relocation to deal with ASLR
> at least on some platforms.
Unfortunately we do not, e.g. if you build cc1/cc1plus as PIE on
x86_64-linux, PCH will stop working unless one always invokes it with
disabled ASLR through personality.
I think this is related to function pointers and pointers to .rodata/.data
etc. variables in GC memory, we currently do not relocate that.
What we perhaps could do is (at least assuming all the ELF PT_LOAD segments
are adjacent with a single load base for them - I think at least ia64
non-PIE binaries were violating this by having .text and .data PT_LOAD
segments many terrabytes appart with a whole in between not protected in any
way, but dunno if that is for PIEs too), perhaps try in a host
specific way remember the address range in which the function pointers and
.rodata/.data can exist, remember the extent start and end from PCH generation
and on PCH load query those addresses for the current compiler and relocate
everything in that extent by the load bias from the last run.
But, the assumption for this is that those function and data/rodata pointers
in GC memory are actually marked at least as pointers...
Do we e.g. have objects with virtual classes in GC memory and if so, do we
catch their virtual table pointers?
Jakub
