Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Thu, May 12, 2016 at 03:09:32PM +0200, Borislav Petkov wrote: > I wanted to have gcc use %[w] and this way not hardcode the reg but the > ABI kinda hardcodes it to rAX. And you're right about tracing funkyness > adding glue so we're probably better off doing the .S thing directly and > making

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Thu, May 12, 2016 at 03:09:32PM +0200, Borislav Petkov wrote: > I wanted to have gcc use %[w] and this way not hardcode the reg but the > ABI kinda hardcodes it to rAX. And you're right about tracing funkyness > adding glue so we're probably better off doing the .S thing directly and > making

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Thu, May 12, 2016 at 02:14:52PM +0200, Peter Zijlstra wrote: > But this is a C function, with C calling convention. You're now assuming > GCC doesn't clobber anything with its prologue/epilogue. > > I think hpa meant to put it in an .S file and avoid all that. I wanted to have gcc use %[w]

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Thu, May 12, 2016 at 02:14:52PM +0200, Peter Zijlstra wrote: > But this is a C function, with C calling convention. You're now assuming > GCC doesn't clobber anything with its prologue/epilogue. > > I think hpa meant to put it in an .S file and avoid all that. I wanted to have gcc use %[w]

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Thu, May 12, 2016 at 01:57:38PM +0200, Borislav Petkov wrote: > #ifdef CONFIG_X86_32 > # define PUSH_DX"pushl %%edx\n\t" > # define POP_DX "popl %%edx\n\t" > #else > # define PUSH_DX"pushq %%rdx\n\t" > # define POP_DX "popq %%rdx\n\t" > #endif > > unsigned int

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Thu, May 12, 2016 at 01:57:38PM +0200, Borislav Petkov wrote: > #ifdef CONFIG_X86_32 > # define PUSH_DX"pushl %%edx\n\t" > # define POP_DX "popl %%edx\n\t" > #else > # define PUSH_DX"pushq %%rdx\n\t" > # define POP_DX "popq %%rdx\n\t" > #endif > > unsigned int

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Wed, May 11, 2016 at 09:54:50PM -0700, H. Peter Anvin wrote: > I was thinking it isn't really very complex code even in assembly as > it is super-regular; you can even crib the gcc-generated code if you > wish. Do I wanna do experiments in asm? Always! :-) Ok, so I did steal gcc -m32 -O3

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Wed, May 11, 2016 at 09:54:50PM -0700, H. Peter Anvin wrote: > I was thinking it isn't really very complex code even in assembly as > it is super-regular; you can even crib the gcc-generated code if you > wish. Do I wanna do experiments in asm? Always! :-) Ok, so I did steal gcc -m32 -O3

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On May 11, 2016 4:24:09 AM PDT, Peter Zijlstra wrote: >On Wed, May 11, 2016 at 07:15:19AM -0400, Brian Gerst wrote: > >> I think he meant the out of line version would be asm, so you could >> control what registers were clobbered. > >Yeah, it might save a few cycles on the

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On May 11, 2016 4:24:09 AM PDT, Peter Zijlstra wrote: >On Wed, May 11, 2016 at 07:15:19AM -0400, Brian Gerst wrote: > >> I think he meant the out of line version would be asm, so you could >> control what registers were clobbered. > >Yeah, it might save a few cycles on the call, but given that

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Wed, May 11, 2016 at 01:24:09PM +0200, Peter Zijlstra wrote: > Yeah, it might save a few cycles on the call, but given that most > machines should have popcnt these days is it worth the hassle/cost of > duplicating the lib/hweight.c magic in asm (and remember, twice, once > for 32bit and once

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Wed, May 11, 2016 at 01:24:09PM +0200, Peter Zijlstra wrote: > Yeah, it might save a few cycles on the call, but given that most > machines should have popcnt these days is it worth the hassle/cost of > duplicating the lib/hweight.c magic in asm (and remember, twice, once > for 32bit and once

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Wed, May 11, 2016 at 07:15:19AM -0400, Brian Gerst wrote: > I think he meant the out of line version would be asm, so you could > control what registers were clobbered. Yeah, it might save a few cycles on the call, but given that most machines should have popcnt these days is it worth the

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Wed, May 11, 2016 at 07:15:19AM -0400, Brian Gerst wrote: > I think he meant the out of line version would be asm, so you could > control what registers were clobbered. Yeah, it might save a few cycles on the call, but given that most machines should have popcnt these days is it worth the

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Wed, May 11, 2016 at 12:11 AM, Borislav Petkov wrote: > On Tue, May 10, 2016 at 03:30:48PM -0700, H. Peter Anvin wrote: >> I didn't mean inline assembly. > > How does that matter? > > The problem is having as less insn bytes as possible and the minimal > size we can do is issuing

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Wed, May 11, 2016 at 12:11 AM, Borislav Petkov wrote: > On Tue, May 10, 2016 at 03:30:48PM -0700, H. Peter Anvin wrote: >> I didn't mean inline assembly. > > How does that matter? > > The problem is having as less insn bytes as possible and the minimal > size we can do is issuing POPCNT

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Tue, May 10, 2016 at 03:30:48PM -0700, H. Peter Anvin wrote: > I didn't mean inline assembly. How does that matter? The problem is having as less insn bytes as possible and the minimal size we can do is issuing POPCNT everywhere which is 4 or 5 bytes. The alternatives then replace that with a

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Tue, May 10, 2016 at 03:30:48PM -0700, H. Peter Anvin wrote: > I didn't mean inline assembly. How does that matter? The problem is having as less insn bytes as possible and the minimal size we can do is issuing POPCNT everywhere which is 4 or 5 bytes. The alternatives then replace that with a

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On 05/10/16 12:10, Borislav Petkov wrote: > On Tue, May 10, 2016 at 12:03:48PM -0700, H. Peter Anvin wrote: >> Also, to be fair... if the problem is with these being in C then we >> could just do it in assembly easily enough. > > I thought about converting the __sw_hweight* variants to asm but >

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On 05/10/16 12:10, Borislav Petkov wrote: > On Tue, May 10, 2016 at 12:03:48PM -0700, H. Peter Anvin wrote: >> Also, to be fair... if the problem is with these being in C then we >> could just do it in assembly easily enough. > > I thought about converting the __sw_hweight* variants to asm but >

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Tue, May 10, 2016 at 12:03:48PM -0700, H. Peter Anvin wrote: > Also, to be fair... if the problem is with these being in C then we > could just do it in assembly easily enough. I thought about converting the __sw_hweight* variants to asm but __sw_hweight32, for example, is 55 bytes here and

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Tue, May 10, 2016 at 12:03:48PM -0700, H. Peter Anvin wrote: > Also, to be fair... if the problem is with these being in C then we > could just do it in assembly easily enough. I thought about converting the __sw_hweight* variants to asm but __sw_hweight32, for example, is 55 bytes here and

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On May 10, 2016 10:23:13 AM PDT, Peter Zijlstra wrote: >On Tue, May 10, 2016 at 06:53:18PM +0200, Borislav Petkov wrote: >> static __always_inline unsigned int __arch_hweight32(unsigned int w) >> { >> -unsigned int res = 0; >> +unsigned int res; >> >> -asm

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On May 10, 2016 10:23:13 AM PDT, Peter Zijlstra wrote: >On Tue, May 10, 2016 at 06:53:18PM +0200, Borislav Petkov wrote: >> static __always_inline unsigned int __arch_hweight32(unsigned int w) >> { >> -unsigned int res = 0; >> +unsigned int res; >> >> -asm (ALTERNATIVE("call

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Tue, May 10, 2016 at 07:23:13PM +0200, Peter Zijlstra wrote: > So what was wrong with using the normal thunk_*.S wrappers for the > calls? That would allow you to use the alternative() stuff which does > generate smaller code. Yeah, so a full allyesconfig vmlinux gives ~22K .text size

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Tue, May 10, 2016 at 07:23:13PM +0200, Peter Zijlstra wrote: > So what was wrong with using the normal thunk_*.S wrappers for the > calls? That would allow you to use the alternative() stuff which does > generate smaller code. Yeah, so a full allyesconfig vmlinux gives ~22K .text size

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Tue, May 10, 2016 at 06:53:18PM +0200, Borislav Petkov wrote: > static __always_inline unsigned int __arch_hweight32(unsigned int w) > { > - unsigned int res = 0; > + unsigned int res; > > - asm (ALTERNATIVE("call __sw_hweight32", POPCNT32, X86_FEATURE_POPCNT) > -

Re: [PATCH -v2] x86/hweight: Get rid of the special calling convention

On Tue, May 10, 2016 at 06:53:18PM +0200, Borislav Petkov wrote: > static __always_inline unsigned int __arch_hweight32(unsigned int w) > { > - unsigned int res = 0; > + unsigned int res; > > - asm (ALTERNATIVE("call __sw_hweight32", POPCNT32, X86_FEATURE_POPCNT) > -

[PATCH -v2] x86/hweight: Get rid of the special calling convention

From: Borislav Petkov <b...@suse.de> Date: Wed, 4 May 2016 18:52:09 +0200 Subject: [PATCH -v2] x86/hweight: Get rid of the special calling convention People complained about ARCH_HWEIGHT_CFLAGS and how it throws a wrench into kcov, lto, etc, experimentation. And its not like we absolutel

[PATCH -v2] x86/hweight: Get rid of the special calling convention

From: Borislav Petkov Date: Wed, 4 May 2016 18:52:09 +0200 Subject: [PATCH -v2] x86/hweight: Get rid of the special calling convention People complained about ARCH_HWEIGHT_CFLAGS and how it throws a wrench into kcov, lto, etc, experimentation. And its not like we absolutely need it so let's get