On Mon, Jul 31, 2023 at 12:16:59PM +0100, Valentin Schneider wrote:
You're quite right - fabricating an artificial warning with a call to __flush_tlb_local():
vmlinux.o: warning: objtool: pv_ops[1]: indirect call to native_flush_tlb_local() leaves .noinstr.text section vmlinux.o: warning: objtool: __flush_tlb_all_noinstr+0x4: call to {dynamic}() leaves .noinstr.text section
Interestingly the second one doesn't seem to have triggered the "pv_ops" bit of call_dest_name. Seems like any call to insn_reloc(NULL, x) will return NULL.
Yeah, that's weird.
Trickling down the file yields:
vmlinux.o: warning: objtool: pv_ops[1]: indirect call to native_flush_tlb_local() leaves .noinstr.text section vmlinux.o: warning: objtool: __flush_tlb_all_noinstr+0x4: call to pv_ops[0]() leaves .noinstr.text section
In my case (!PARAVIRT_XXL) pv_ops should look like: [0]: .cpu.io_delay [1]: .mmu.flush_tlb_user()
so pv_ops[1] looks right. Seems like pv_call_dest() gets it right because it uses arch_dest_reloc_offset().
If I use the above to fix up validate_call(), would we still need pv_call_dest() & co?
The functionality in pv_call_dest() is still needed because it goes through all the possible targets for the .mmu.flush_tlb_user() pointer -- xen_flush_tlb() and native_flush_tlb_local() -- and makes sure they're noinstr.
Ideally it would only print a single warning for this case, something like:
vmlinux.o: warning: objtool: __flush_tlb_all_noinstr+0x4: indirect call to native_flush_tlb_local() leaves .noinstr.text section
I left out "pv_ops[1]" because it's already long enough :-)
It would need a little bit of code shuffling. But it's really a preexisting problem so don't feel compelled to fix it with this patch set.