On Thu, Jan 16, 2014 at 05:43:44PM +0000, Will Deacon wrote:
> > + struct vm_unmapped_area_info info =
> > + {
> > + .flags = 0,
> > + .length = vdso_mapping_len,
> > + .low_limit = mm->mmap_base,
> > + .high_limit = TASK_SIZE,
> > + .align_mask = (1 << 16) - 1,
> > + };
> > + vdso_base = vm_unmapped_area(&info);
> > + }
>
> I don't like this fix. The kernel is perfectly alright mapping the vdso at
> the actual page size, as opposed to the maximum. Since the vdso isn't
> demand-paged, we can actually just tell the linker not to bother forcing 64k
> (worst case) alignment for PT_LOAD segments. Please can you try the patch
> below?
>
Me either, tbh. ;-)
I was testing out using -Wl,-z,max-page-size for the
!CONFIG_ARM64_64K_PAGES case, and that seemed to work. A quick compile
check shows the segment alignment being 0x10 with -Wl,-n:
kmcmarti ~/linux $ eu-readelf -l
arch/arm64/kernel/vdso/vdso.so
Program Headers:
Type Offset VirtAddr PhysAddr FileSiz
MemSiz Flg Align
LOAD 0x000000 0x0000000000000000 0x0000000000000000 0x000700
0x000700 R E 0x10
so I think that should work nicely!
I'll reboot a machine with this fix to test it as soon as possible.
Acked-by: Kyle McMartin <k...@redhat.com>
> --- a/arch/arm64/kernel/vdso/Makefile
> +++ b/arch/arm64/kernel/vdso/Makefile
> @@ -48,7 +48,7 @@ $(obj-vdso): %.o: %.S
>
> # Actual build commands
> quiet_cmd_vdsold = VDSOL $@
> - cmd_vdsold = $(CC) $(c_flags) -Wl,-T $^ -o $@
> + cmd_vdsold = $(CC) $(c_flags) -Wl,-n -Wl,-T $^ -o $@
> quiet_cmd_vdsoas = VDSOA $@
> cmd_vdsoas = $(CC) $(a_flags) -c -o $@ $<
>
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