Re: x86-64: Maintain 16-byte stack alignment

On Fri, Jan 13, 2017 at 04:36:48PM +0800, Herbert Xu wrote: > On Thu, Jan 12, 2017 at 12:08:07PM -0800, Andy Lutomirski wrote: > > > > I think we have some inline functions that do asm volatile ("call > > ..."), and I don't see any credible way of forcing alignment short of > > generating an

Re: x86-64: Maintain 16-byte stack alignment

On Fri, Jan 13, 2017 at 04:36:48PM +0800, Herbert Xu wrote: > On Thu, Jan 12, 2017 at 12:08:07PM -0800, Andy Lutomirski wrote: > > > > I think we have some inline functions that do asm volatile ("call > > ..."), and I don't see any credible way of forcing alignment short of > > generating an

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 11:07:09PM -0600, Josh Poimboeuf wrote: > > Disabling frame pointers didn't seem to help, but I finally got it to > misalign with a different test case. I think it had been aligning the > array, so instead I made it push a register. Right. If you start manipulating the

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 11:07:09PM -0600, Josh Poimboeuf wrote: > > Disabling frame pointers didn't seem to help, but I finally got it to > misalign with a different test case. I think it had been aligning the > array, so instead I made it push a register. Right. If you start manipulating the

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 08:37:18PM -0800, Linus Torvalds wrote: > > So then the compiler actually needs to start adding useless instructions > just to keep the stack 16-byte aligned. Which it does. Of course most of the time no extra instructions are required because there are stack variables,

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 08:37:18PM -0800, Linus Torvalds wrote: > > So then the compiler actually needs to start adding useless instructions > just to keep the stack 16-byte aligned. Which it does. Of course most of the time no extra instructions are required because there are stack variables,

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 05:46:55PM -0800, Andy Lutomirski wrote: > > What I mean is: what guarantees that the stack is properly aligned for > the subroutine call? gcc promises to set up a stack frame, but does > it promise that rsp will be properly aligned to call a C function? Yes, as long as

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 05:46:55PM -0800, Andy Lutomirski wrote: > > What I mean is: what guarantees that the stack is properly aligned for > the subroutine call? gcc promises to set up a stack frame, but does > it promise that rsp will be properly aligned to call a C function? Yes, as long as

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 01:40:54PM -0800, Linus Torvalds wrote: > > The 8-byte alignment mainly makes sense when the basic call sequence > just adds 8 bytes, and you have functions without frames (that still > call other functions). The question is does it really make sense to save those 8 bytes

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 01:40:54PM -0800, Linus Torvalds wrote: > > The 8-byte alignment mainly makes sense when the basic call sequence > just adds 8 bytes, and you have functions without frames (that still > call other functions). The question is does it really make sense to save those 8 bytes

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 12:08:07PM -0800, Andy Lutomirski wrote: > > I think we have some inline functions that do asm volatile ("call > ..."), and I don't see any credible way of forcing alignment short of > generating an entirely new stack frame and aligning that. Ick. This A straight asm

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 12:08:07PM -0800, Andy Lutomirski wrote: > > I think we have some inline functions that do asm volatile ("call > ..."), and I don't see any credible way of forcing alignment short of > generating an entirely new stack frame and aligning that. Ick. This A straight asm

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 08:37:18PM -0800, Linus Torvalds wrote: > On Jan 12, 2017 8:28 PM, "Josh Poimboeuf" wrote: > > > The stack frame was always 16-byte aligned regardless of whether the > buf array size was even or odd. > > > Including with -fomit-frame-pointer? > >

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 08:37:18PM -0800, Linus Torvalds wrote: > On Jan 12, 2017 8:28 PM, "Josh Poimboeuf" wrote: > > > The stack frame was always 16-byte aligned regardless of whether the > buf array size was even or odd. > > > Including with -fomit-frame-pointer? > > With frame pointers,

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 07:23:18PM -0800, Andy Lutomirski wrote: > On Thu, Jan 12, 2017 at 7:11 PM, Josh Poimboeuf wrote: > > On Thu, Jan 12, 2017 at 05:46:55PM -0800, Andy Lutomirski wrote: > >> On Thu, Jan 12, 2017 at 12:15 PM, Josh Poimboeuf > >>

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 07:23:18PM -0800, Andy Lutomirski wrote: > On Thu, Jan 12, 2017 at 7:11 PM, Josh Poimboeuf wrote: > > On Thu, Jan 12, 2017 at 05:46:55PM -0800, Andy Lutomirski wrote: > >> On Thu, Jan 12, 2017 at 12:15 PM, Josh Poimboeuf > >> wrote: > >> > On Thu, Jan 12, 2017 at

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 7:11 PM, Josh Poimboeuf wrote: > On Thu, Jan 12, 2017 at 05:46:55PM -0800, Andy Lutomirski wrote: >> On Thu, Jan 12, 2017 at 12:15 PM, Josh Poimboeuf wrote: >> > On Thu, Jan 12, 2017 at 12:08:07PM -0800, Andy Lutomirski wrote: >>

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 7:11 PM, Josh Poimboeuf wrote: > On Thu, Jan 12, 2017 at 05:46:55PM -0800, Andy Lutomirski wrote: >> On Thu, Jan 12, 2017 at 12:15 PM, Josh Poimboeuf wrote: >> > On Thu, Jan 12, 2017 at 12:08:07PM -0800, Andy Lutomirski wrote: >> >> On Thu, Jan 12, 2017 at 11:51 AM, Linus

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 05:46:55PM -0800, Andy Lutomirski wrote: > On Thu, Jan 12, 2017 at 12:15 PM, Josh Poimboeuf wrote: > > On Thu, Jan 12, 2017 at 12:08:07PM -0800, Andy Lutomirski wrote: > >> On Thu, Jan 12, 2017 at 11:51 AM, Linus Torvalds > >>

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 05:46:55PM -0800, Andy Lutomirski wrote: > On Thu, Jan 12, 2017 at 12:15 PM, Josh Poimboeuf wrote: > > On Thu, Jan 12, 2017 at 12:08:07PM -0800, Andy Lutomirski wrote: > >> On Thu, Jan 12, 2017 at 11:51 AM, Linus Torvalds > >> wrote: > >> > On Thu, Jan 12, 2017 at 6:02

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 12:15 PM, Josh Poimboeuf wrote: > On Thu, Jan 12, 2017 at 12:08:07PM -0800, Andy Lutomirski wrote: >> On Thu, Jan 12, 2017 at 11:51 AM, Linus Torvalds >> wrote: >> > On Thu, Jan 12, 2017 at 6:02 AM, Josh Poimboeuf

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 12:15 PM, Josh Poimboeuf wrote: > On Thu, Jan 12, 2017 at 12:08:07PM -0800, Andy Lutomirski wrote: >> On Thu, Jan 12, 2017 at 11:51 AM, Linus Torvalds >> wrote: >> > On Thu, Jan 12, 2017 at 6:02 AM, Josh Poimboeuf >> > wrote: >> >> >> >> Just to clarify, I think you're

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 12:55 PM, Josh Poimboeuf wrote: > > - Who's going to run sparse all the time to catch unauthorized users of > __aligned__(16)? Well, considering that we apparently only have a small handful of existing users without anybody having ever run any tool

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 12:55 PM, Josh Poimboeuf wrote: > > - Who's going to run sparse all the time to catch unauthorized users of > __aligned__(16)? Well, considering that we apparently only have a small handful of existing users without anybody having ever run any tool at all, I don't think

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 02:15:11PM -0600, Josh Poimboeuf wrote: > On Thu, Jan 12, 2017 at 12:08:07PM -0800, Andy Lutomirski wrote: > > On Thu, Jan 12, 2017 at 11:51 AM, Linus Torvalds > > wrote: > > > On Thu, Jan 12, 2017 at 6:02 AM, Josh Poimboeuf

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 02:15:11PM -0600, Josh Poimboeuf wrote: > On Thu, Jan 12, 2017 at 12:08:07PM -0800, Andy Lutomirski wrote: > > On Thu, Jan 12, 2017 at 11:51 AM, Linus Torvalds > > wrote: > > > On Thu, Jan 12, 2017 at 6:02 AM, Josh Poimboeuf > > > wrote: > > >> > > >> Just to clarify, I

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 12:08:07PM -0800, Andy Lutomirski wrote: > On Thu, Jan 12, 2017 at 11:51 AM, Linus Torvalds > wrote: > > On Thu, Jan 12, 2017 at 6:02 AM, Josh Poimboeuf wrote: > >> > >> Just to clarify, I think you're asking if, for

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 12:08:07PM -0800, Andy Lutomirski wrote: > On Thu, Jan 12, 2017 at 11:51 AM, Linus Torvalds > wrote: > > On Thu, Jan 12, 2017 at 6:02 AM, Josh Poimboeuf wrote: > >> > >> Just to clarify, I think you're asking if, for versions of gcc which > >> don't support

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 11:51 AM, Linus Torvalds wrote: > On Thu, Jan 12, 2017 at 6:02 AM, Josh Poimboeuf wrote: >> >> Just to clarify, I think you're asking if, for versions of gcc which >> don't support -mpreferred-stack-boundary=3, objtool

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 11:51 AM, Linus Torvalds wrote: > On Thu, Jan 12, 2017 at 6:02 AM, Josh Poimboeuf wrote: >> >> Just to clarify, I think you're asking if, for versions of gcc which >> don't support -mpreferred-stack-boundary=3, objtool can analyze all C >> functions to ensure their stacks

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 6:02 AM, Josh Poimboeuf wrote: > > Just to clarify, I think you're asking if, for versions of gcc which > don't support -mpreferred-stack-boundary=3, objtool can analyze all C > functions to ensure their stacks are 16-byte aligned. > > It's certainly

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 6:02 AM, Josh Poimboeuf wrote: > > Just to clarify, I think you're asking if, for versions of gcc which > don't support -mpreferred-stack-boundary=3, objtool can analyze all C > functions to ensure their stacks are 16-byte aligned. > > It's certainly possible, but I don't

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 11:06:50PM +0800, Herbert Xu wrote: > On Thu, Jan 12, 2017 at 09:03:18AM -0600, Josh Poimboeuf wrote: > > > > For the entry code, could we just replace all calls with CALL_ALIGNED? > > That might be less intrusive than trying to adjust all the pt_regs > > accesses. > > >

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 11:06:50PM +0800, Herbert Xu wrote: > On Thu, Jan 12, 2017 at 09:03:18AM -0600, Josh Poimboeuf wrote: > > > > For the entry code, could we just replace all calls with CALL_ALIGNED? > > That might be less intrusive than trying to adjust all the pt_regs > > accesses. > > >

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 09:03:18AM -0600, Josh Poimboeuf wrote: > On Wed, Jan 11, 2017 at 11:51:10PM -0800, Andy Lutomirski wrote: > > On Wed, Jan 11, 2017 at 11:05 PM, Herbert Xu > > wrote: > > > On Tue, Jan 10, 2017 at 09:05:28AM -0800, Linus Torvalds wrote: > > >>

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 09:03:18AM -0600, Josh Poimboeuf wrote: > On Wed, Jan 11, 2017 at 11:51:10PM -0800, Andy Lutomirski wrote: > > On Wed, Jan 11, 2017 at 11:05 PM, Herbert Xu > > wrote: > > > On Tue, Jan 10, 2017 at 09:05:28AM -0800, Linus Torvalds wrote: > > >> > > >> I'm pretty sure we

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 09:03:18AM -0600, Josh Poimboeuf wrote: > > For the entry code, could we just replace all calls with CALL_ALIGNED? > That might be less intrusive than trying to adjust all the pt_regs > accesses. > > Then to ensure that nobody ever uses 'call' directly: > > '#define

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 09:03:18AM -0600, Josh Poimboeuf wrote: > > For the entry code, could we just replace all calls with CALL_ALIGNED? > That might be less intrusive than trying to adjust all the pt_regs > accesses. > > Then to ensure that nobody ever uses 'call' directly: > > '#define

Re: x86-64: Maintain 16-byte stack alignment

On Wed, Jan 11, 2017 at 11:51:10PM -0800, Andy Lutomirski wrote: > On Wed, Jan 11, 2017 at 11:05 PM, Herbert Xu > wrote: > > On Tue, Jan 10, 2017 at 09:05:28AM -0800, Linus Torvalds wrote: > >> > >> I'm pretty sure we have random asm code that may not maintain a > >>

Re: x86-64: Maintain 16-byte stack alignment

On Wed, Jan 11, 2017 at 11:51:10PM -0800, Andy Lutomirski wrote: > On Wed, Jan 11, 2017 at 11:05 PM, Herbert Xu > wrote: > > On Tue, Jan 10, 2017 at 09:05:28AM -0800, Linus Torvalds wrote: > >> > >> I'm pretty sure we have random asm code that may not maintain a > >> 16-byte stack alignment when

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 08:46:01AM +0100, Ingo Molnar wrote: > > * Herbert Xu wrote: > > > On Tue, Jan 10, 2017 at 09:05:28AM -0800, Linus Torvalds wrote: > > > > > > I'm pretty sure we have random asm code that may not maintain a > > > 16-byte stack alignment when

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 08:46:01AM +0100, Ingo Molnar wrote: > > * Herbert Xu wrote: > > > On Tue, Jan 10, 2017 at 09:05:28AM -0800, Linus Torvalds wrote: > > > > > > I'm pretty sure we have random asm code that may not maintain a > > > 16-byte stack alignment when it calls other code

Re: x86-64: Maintain 16-byte stack alignment

On Wed, Jan 11, 2017 at 10:21:07PM -0800, Andy Lutomirski wrote: > On Tue, Jan 10, 2017 at 10:01 PM, Andy Lutomirski wrote: > > On Tue, Jan 10, 2017 at 8:35 PM, Herbert Xu > > wrote: > >> On Tue, Jan 10, 2017 at 08:17:17PM -0800, Linus Torvalds

Re: x86-64: Maintain 16-byte stack alignment

On Wed, Jan 11, 2017 at 10:21:07PM -0800, Andy Lutomirski wrote: > On Tue, Jan 10, 2017 at 10:01 PM, Andy Lutomirski wrote: > > On Tue, Jan 10, 2017 at 8:35 PM, Herbert Xu > > wrote: > >> On Tue, Jan 10, 2017 at 08:17:17PM -0800, Linus Torvalds wrote: > >>> > >>> That said, I do think that the

Re: x86-64: Maintain 16-byte stack alignment

* Herbert Xu wrote: > > But if we can't do this with automatic verification, then I'm not sure > > I want to do it at all. The asm is already more precarious than I'd > > like, and having a code path that is misaligned is asking for obscure > > bugs down the road.

Re: x86-64: Maintain 16-byte stack alignment

* Herbert Xu wrote: > > But if we can't do this with automatic verification, then I'm not sure > > I want to do it at all. The asm is already more precarious than I'd > > like, and having a code path that is misaligned is asking for obscure > > bugs down the road. > > I understand the need

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 08:01:51AM +, Ard Biesheuvel wrote: > > [From memory] the arm64 ELF psABI mandates a 16 byte stack alignment > at function entry, and 8 byte alignment at all other times. This means > compiled code will typically preserve 16 byte alignment, and > __aligned(16) on a

Re: x86-64: Maintain 16-byte stack alignment

On Thu, Jan 12, 2017 at 08:01:51AM +, Ard Biesheuvel wrote: > > [From memory] the arm64 ELF psABI mandates a 16 byte stack alignment > at function entry, and 8 byte alignment at all other times. This means > compiled code will typically preserve 16 byte alignment, and > __aligned(16) on a

Re: x86-64: Maintain 16-byte stack alignment

On Wed, Jan 11, 2017 at 11:51:10PM -0800, Andy Lutomirski wrote: > > The problem is that we have nasties like TRACE_IRQS_OFF. Performance I don't understand. What's the issue with TRACE_IRQS_OFF? It should be treated as any other function call. That is, enter it with an aligned stack, and the

Re: x86-64: Maintain 16-byte stack alignment

On Wed, Jan 11, 2017 at 11:51:10PM -0800, Andy Lutomirski wrote: > > The problem is that we have nasties like TRACE_IRQS_OFF. Performance I don't understand. What's the issue with TRACE_IRQS_OFF? It should be treated as any other function call. That is, enter it with an aligned stack, and the

Re: x86-64: Maintain 16-byte stack alignment

On 12 January 2017 at 06:12, Herbert Xu wrote: > On Tue, Jan 10, 2017 at 05:30:48PM +, Ard Biesheuvel wrote: >> >> Apologies for introducing this breakage. It seemed like an obvious and >> simple cleanup, so I didn't even bother to mention it in the commit >> log,

Re: x86-64: Maintain 16-byte stack alignment

On 12 January 2017 at 06:12, Herbert Xu wrote: > On Tue, Jan 10, 2017 at 05:30:48PM +, Ard Biesheuvel wrote: >> >> Apologies for introducing this breakage. It seemed like an obvious and >> simple cleanup, so I didn't even bother to mention it in the commit >> log, but if the kernel does not

Re: x86-64: Maintain 16-byte stack alignment

On Wed, Jan 11, 2017 at 11:05 PM, Herbert Xu wrote: > On Tue, Jan 10, 2017 at 09:05:28AM -0800, Linus Torvalds wrote: >> >> I'm pretty sure we have random asm code that may not maintain a >> 16-byte stack alignment when it calls other code (including, in some >>

Re: x86-64: Maintain 16-byte stack alignment

On Wed, Jan 11, 2017 at 11:05 PM, Herbert Xu wrote: > On Tue, Jan 10, 2017 at 09:05:28AM -0800, Linus Torvalds wrote: >> >> I'm pretty sure we have random asm code that may not maintain a >> 16-byte stack alignment when it calls other code (including, in some >> cases, calling C code). >> >> So

Re: x86-64: Maintain 16-byte stack alignment

* Herbert Xu wrote: > On Tue, Jan 10, 2017 at 09:05:28AM -0800, Linus Torvalds wrote: > > > > I'm pretty sure we have random asm code that may not maintain a > > 16-byte stack alignment when it calls other code (including, in some > > cases, calling C code). > > >

Re: x86-64: Maintain 16-byte stack alignment

* Herbert Xu wrote: > On Tue, Jan 10, 2017 at 09:05:28AM -0800, Linus Torvalds wrote: > > > > I'm pretty sure we have random asm code that may not maintain a > > 16-byte stack alignment when it calls other code (including, in some > > cases, calling C code). > > > > So I'm not at all convinced

Re: x86-64: Maintain 16-byte stack alignment

* Andy Lutomirski wrote: > I find it rather annoying that gcc before 4.8 malfunctions when it > sees __aligned__(16) on x86_64 kernels. Sigh. Ran into this when writing silly FPU in-kernel testcases a couple of months ago... Thanks, Ingo

Re: x86-64: Maintain 16-byte stack alignment

* Andy Lutomirski wrote: > I find it rather annoying that gcc before 4.8 malfunctions when it > sees __aligned__(16) on x86_64 kernels. Sigh. Ran into this when writing silly FPU in-kernel testcases a couple of months ago... Thanks, Ingo

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 09:05:28AM -0800, Linus Torvalds wrote: > > I'm pretty sure we have random asm code that may not maintain a > 16-byte stack alignment when it calls other code (including, in some > cases, calling C code). > > So I'm not at all convinced that this is a good idea. We

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 09:05:28AM -0800, Linus Torvalds wrote: > > I'm pretty sure we have random asm code that may not maintain a > 16-byte stack alignment when it calls other code (including, in some > cases, calling C code). > > So I'm not at all convinced that this is a good idea. We

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 10:01 PM, Andy Lutomirski wrote: > On Tue, Jan 10, 2017 at 8:35 PM, Herbert Xu > wrote: >> On Tue, Jan 10, 2017 at 08:17:17PM -0800, Linus Torvalds wrote: >>> >>> That said, I do think that the "don't assume stack

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 10:01 PM, Andy Lutomirski wrote: > On Tue, Jan 10, 2017 at 8:35 PM, Herbert Xu > wrote: >> On Tue, Jan 10, 2017 at 08:17:17PM -0800, Linus Torvalds wrote: >>> >>> That said, I do think that the "don't assume stack alignment, do it by >>> hand" may be the safer thing.

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 05:30:48PM +, Ard Biesheuvel wrote: > > Apologies for introducing this breakage. It seemed like an obvious and > simple cleanup, so I didn't even bother to mention it in the commit > log, but if the kernel does not guarantee 16 byte alignment, I guess > we should revert

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 05:30:48PM +, Ard Biesheuvel wrote: > > Apologies for introducing this breakage. It seemed like an obvious and > simple cleanup, so I didn't even bother to mention it in the commit > log, but if the kernel does not guarantee 16 byte alignment, I guess > we should revert

Re: x86-64: Maintain 16-byte stack alignment

On Wed, Jan 11, 2017 at 12:09 AM, Herbert Xu wrote: > On Wed, Jan 11, 2017 at 08:06:54AM +, Ard Biesheuvel wrote: >> >> Couldn't we update the __aligned(x) macro to emit 32 if arch == x86 >> and x == 16? All other cases should work just fine afaict > > Not

Re: x86-64: Maintain 16-byte stack alignment

On Wed, Jan 11, 2017 at 12:09 AM, Herbert Xu wrote: > On Wed, Jan 11, 2017 at 08:06:54AM +, Ard Biesheuvel wrote: >> >> Couldn't we update the __aligned(x) macro to emit 32 if arch == x86 >> and x == 16? All other cases should work just fine afaict > > Not everyone uses that macro. You'd

Re: x86-64: Maintain 16-byte stack alignment

On Wed, Jan 11, 2017 at 08:06:54AM +, Ard Biesheuvel wrote: > > Couldn't we update the __aligned(x) macro to emit 32 if arch == x86 > and x == 16? All other cases should work just fine afaict Not everyone uses that macro. You'd also need to add some checks to stop people from using the gcc

Re: x86-64: Maintain 16-byte stack alignment

On Wed, Jan 11, 2017 at 08:06:54AM +, Ard Biesheuvel wrote: > > Couldn't we update the __aligned(x) macro to emit 32 if arch == x86 > and x == 16? All other cases should work just fine afaict Not everyone uses that macro. You'd also need to add some checks to stop people from using the gcc

Re: x86-64: Maintain 16-byte stack alignment

On 11 January 2017 at 06:53, Linus Torvalds wrote: > > > On Jan 10, 2017 8:36 PM, "Herbert Xu" wrote: > > > Sure we can ban the use of attribute aligned on stacks. But > what about indirect uses through structures? > > > It should be

Re: x86-64: Maintain 16-byte stack alignment

On 11 January 2017 at 06:53, Linus Torvalds wrote: > > > On Jan 10, 2017 8:36 PM, "Herbert Xu" wrote: > > > Sure we can ban the use of attribute aligned on stacks. But > what about indirect uses through structures? > > > It should be pretty trivial to add a sparse warning for that, though. >

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 8:35 PM, Herbert Xu wrote: > On Tue, Jan 10, 2017 at 08:17:17PM -0800, Linus Torvalds wrote: >> >> That said, I do think that the "don't assume stack alignment, do it by >> hand" may be the safer thing. Because who knows what the random rules

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 8:35 PM, Herbert Xu wrote: > On Tue, Jan 10, 2017 at 08:17:17PM -0800, Linus Torvalds wrote: >> >> That said, I do think that the "don't assume stack alignment, do it by >> hand" may be the safer thing. Because who knows what the random rules >> will be on other

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 08:17:17PM -0800, Linus Torvalds wrote: > > That said, I do think that the "don't assume stack alignment, do it by > hand" may be the safer thing. Because who knows what the random rules > will be on other architectures. Sure we can ban the use of attribute aligned on

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 08:17:17PM -0800, Linus Torvalds wrote: > > That said, I do think that the "don't assume stack alignment, do it by > hand" may be the safer thing. Because who knows what the random rules > will be on other architectures. Sure we can ban the use of attribute aligned on

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 7:30 PM, Linus Torvalds wrote: > > If you really want more stack alignment, you have to generate that > alignment yourself by hand (and have a bigger buffer that you do that > alignment inside). Side note: gcc can (and does) actually

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 7:30 PM, Linus Torvalds wrote: > > If you really want more stack alignment, you have to generate that > alignment yourself by hand (and have a bigger buffer that you do that > alignment inside). Side note: gcc can (and does) actually generate forced alignment using "and"

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 7:11 PM, Herbert Xu wrote: > > Well the only other alternative I see is to ban compilers which > enforce 16-byte stack alignment, such as gcc 4.7.2. No, you don't have to ban the compiler - it's just a "generate overly stupid code that just

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 7:11 PM, Herbert Xu wrote: > > Well the only other alternative I see is to ban compilers which > enforce 16-byte stack alignment, such as gcc 4.7.2. No, you don't have to ban the compiler - it's just a "generate overly stupid code that just uses extra instructions to

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 03:25:47PM -0800, Andy Lutomirski wrote: > > > If it does what it says on the tin, it should fix the issue, but after > > adding the attribute, I get the exact same object output, so there's > > something dodgy going on here. > > Ugh, that's annoying. Maybe it needs

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 03:25:47PM -0800, Andy Lutomirski wrote: > > > If it does what it says on the tin, it should fix the issue, but after > > adding the attribute, I get the exact same object output, so there's > > something dodgy going on here. > > Ugh, that's annoying. Maybe it needs

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 11:22:15AM -0800, Andy Lutomirski wrote: > > > Actually, the breakage is introduced by the patch Herbert refers to > > > > https://patchwork.kernel.org/patch/9468391/ > > > > where the state is replaced by a simple > > > > u32 state[16] __aligned(CHACHA20_STATE_ALIGN); > >

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 11:22:15AM -0800, Andy Lutomirski wrote: > > > Actually, the breakage is introduced by the patch Herbert refers to > > > > https://patchwork.kernel.org/patch/9468391/ > > > > where the state is replaced by a simple > > > > u32 state[16] __aligned(CHACHA20_STATE_ALIGN); > >

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 11:00:31AM -0800, Andy Lutomirski wrote: > > Here's what I think is really going on. This is partially from > memory, so I could be off base. The kernel is up against > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53383, which means that, > on some GCC versions (like the

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 11:00:31AM -0800, Andy Lutomirski wrote: > > Here's what I think is really going on. This is partially from > memory, so I could be off base. The kernel is up against > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53383, which means that, > on some GCC versions (like the

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 05:30:48PM +, Ard Biesheuvel wrote: > > Apologies for introducing this breakage. It seemed like an obvious and > simple cleanup, so I didn't even bother to mention it in the commit > log, but if the kernel does not guarantee 16 byte alignment, I guess > we should

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 05:30:48PM +, Ard Biesheuvel wrote: > > Apologies for introducing this breakage. It seemed like an obvious and > simple cleanup, so I didn't even bother to mention it in the commit > log, but if the kernel does not guarantee 16 byte alignment, I guess > we should

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 09:05:28AM -0800, Linus Torvalds wrote: > On Tue, Jan 10, 2017 at 6:39 AM, Herbert Xu > wrote: > > > > BTW this is with Debian gcc 4.7.2 which does not allow an 8-byte > > stack alignment as attempted by the Makefile: > > I'm pretty sure we

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 09:05:28AM -0800, Linus Torvalds wrote: > On Tue, Jan 10, 2017 at 6:39 AM, Herbert Xu > wrote: > > > > BTW this is with Debian gcc 4.7.2 which does not allow an 8-byte > > stack alignment as attempted by the Makefile: > > I'm pretty sure we have random asm code that may

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 12:00 PM, Ard Biesheuvel wrote: > On 10 January 2017 at 19:22, Andy Lutomirski wrote: >> On Tue, Jan 10, 2017 at 11:16 AM, Ard Biesheuvel >> wrote: >>> On 10 January 2017 at 19:00, Andy Lutomirski

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 12:00 PM, Ard Biesheuvel wrote: > On 10 January 2017 at 19:22, Andy Lutomirski wrote: >> On Tue, Jan 10, 2017 at 11:16 AM, Ard Biesheuvel >> wrote: >>> On 10 January 2017 at 19:00, Andy Lutomirski wrote: On Tue, Jan 10, 2017 at 9:30 AM, Ard Biesheuvel wrote:

Re: x86-64: Maintain 16-byte stack alignment

On 10 January 2017 at 19:22, Andy Lutomirski wrote: > On Tue, Jan 10, 2017 at 11:16 AM, Ard Biesheuvel > wrote: >> On 10 January 2017 at 19:00, Andy Lutomirski wrote: >>> On Tue, Jan 10, 2017 at 9:30 AM, Ard Biesheuvel >>>

Re: x86-64: Maintain 16-byte stack alignment

On 10 January 2017 at 19:22, Andy Lutomirski wrote: > On Tue, Jan 10, 2017 at 11:16 AM, Ard Biesheuvel > wrote: >> On 10 January 2017 at 19:00, Andy Lutomirski wrote: >>> On Tue, Jan 10, 2017 at 9:30 AM, Ard Biesheuvel >>> wrote: On 10 January 2017 at 14:33, Herbert Xu wrote: >

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 9:30 AM, Ard Biesheuvel wrote: > On 10 January 2017 at 14:33, Herbert Xu wrote: >> I recently applied the patch >> >> https://patchwork.kernel.org/patch/9468391/ >> >> and ended up with a boot crash when it

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 9:30 AM, Ard Biesheuvel wrote: > On 10 January 2017 at 14:33, Herbert Xu wrote: >> I recently applied the patch >> >> https://patchwork.kernel.org/patch/9468391/ >> >> and ended up with a boot crash when it tried to run the x86 chacha20 >> code. It turned out

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 11:16 AM, Ard Biesheuvel wrote: > On 10 January 2017 at 19:00, Andy Lutomirski wrote: >> On Tue, Jan 10, 2017 at 9:30 AM, Ard Biesheuvel >> wrote: >>> On 10 January 2017 at 14:33, Herbert Xu

Re: x86-64: Maintain 16-byte stack alignment

On Tue, Jan 10, 2017 at 11:16 AM, Ard Biesheuvel wrote: > On 10 January 2017 at 19:00, Andy Lutomirski wrote: >> On Tue, Jan 10, 2017 at 9:30 AM, Ard Biesheuvel >> wrote: >>> On 10 January 2017 at 14:33, Herbert Xu wrote: I recently applied the patch

Re: x86-64: Maintain 16-byte stack alignment

On 10 January 2017 at 19:00, Andy Lutomirski wrote: > On Tue, Jan 10, 2017 at 9:30 AM, Ard Biesheuvel > wrote: >> On 10 January 2017 at 14:33, Herbert Xu wrote: >>> I recently applied the patch >>> >>>

Re: x86-64: Maintain 16-byte stack alignment

On 10 January 2017 at 19:00, Andy Lutomirski wrote: > On Tue, Jan 10, 2017 at 9:30 AM, Ard Biesheuvel > wrote: >> On 10 January 2017 at 14:33, Herbert Xu wrote: >>> I recently applied the patch >>> >>> https://patchwork.kernel.org/patch/9468391/ >>> >>> and ended up with a boot crash

Re: x86-64: Maintain 16-byte stack alignment

On 10 January 2017 at 14:33, Herbert Xu wrote: > I recently applied the patch > > https://patchwork.kernel.org/patch/9468391/ > > and ended up with a boot crash when it tried to run the x86 chacha20 > code. It turned out that the patch changed a manually

Re: x86-64: Maintain 16-byte stack alignment

On 10 January 2017 at 14:33, Herbert Xu wrote: > I recently applied the patch > > https://patchwork.kernel.org/patch/9468391/ > > and ended up with a boot crash when it tried to run the x86 chacha20 > code. It turned out that the patch changed a manually aligned > stack buffer to one

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