On Mon, Mar 16, 2020 at 10:55:00AM +0000, Vincenzo Frascino wrote: > On 3/16/20 10:34 AM, Catalin Marinas wrote: > >> I tried to fine grain the headers as much as I could in order to avoid > >> unneeded/unwanted inclusions: > >> * TASK_SIZE_32 is used to verify ABI consistency on vdso32 (please refer to > >> arch/arm64/kernel/vdso32/vgettimeofday.c). > > > > I see. But the test is probably useless. With 4K pages, TASK_SIZE_32 is > > 1UL << 32, so you can't have a u32 greater than this. So I'd argue that > > the ABI compatibility here doesn't matter. > > > > With 16K or 64K pages, TASK_SIZE_32 is slightly smaller but arm32 never > > supported it. > > > > What's the side-effect of dropping this check altogether? > > The main side-effect is that arm32 and arm64 compat have a different behavior, > that it is what we want to avoid. > > The vdsotest [1] I am using, verifies all the side conditions with respect to > the ABI, which we are now compatible with. Removing those checks would break > this condition. As I said above, I don't see how removing 'if ((u32)ts >= (1UL << 32))' makes any difference. This check was likely removed by the compiler already. Also, userspace doesn't have a trivial way to figure out TASK_SIZE and I can't see anything that tests this in the vdsotest (though I haven't spent that much time looking). If it's hard-coded, note that arm32 TASK_SIZE is different from TASK_SIZE_32 on arm64. Can you tell what actually is failing in vdsotest if you remove the TASK_SIZE_32 checks in the arm64 compat vdso? -- Catalin
