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Re: Compile Assembly and C files together

Subject Re: Compile Assembly and C files together
Newsgroups comp.lang.c
References (1 earlier) <p7ltie$8t5$3@toylet.eternal-september.org> <p7m6g4$93a$1@dont-email.me> <20180306145910.01512e6b@Mars> <p7mcge$oci$1@dont-email.me> <09640d63-f1b3-43c5-970d-4ac66db41cf3@googlegroups.com>
From bartc <bc@freeuk.com>
Message-ID <hrznC.15256$5c2.6550@fx09.am4> (permalink)
Organization virginmedia.com
Date 2018-03-06 16:35 +0000

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On 06/03/2018 15:57, supercat@casperkitty.com wrote:
> On Tuesday, March 6, 2018 at 9:35:52 AM UTC-6, David Brown wrote:
>> On 06/03/18 15:59, Rob Morley wrote:
>>> That's handy.  Although the last time I wrote any assembler was about
>>> 20 years ago, I still might ...
>>>
>>
>> It is not good advice.  At best it gives you a very limited idea of the
>> calling conventions and registers usage.  If you really want to write
>> pure assembly functions that interact with code in other languages, you
>> have to read up on the calling conventions and ABI for the target (and,
>> if it is Windows, for the compiler you are using - the ABI is not
>> standardised on Windows).
>>
>> If you are using gcc (or clang, or icc, or a few other compilers) and
>> you are writing short pieces of assembly, you would be better off
>> learning about gcc's inline assembly support.  Then the compiler takes
>> care of all the interface between the assembly and C.
> 
> If one needs to use a small assembly-language routine to accomplish some
> purpose, and won't be writing a lot of assembly language on the development
> system, letting a compiler generate a stub function for e.g.
> 
>      extern volatile void*pp1,*pp2;
>      extern volatile int nn;
> 
>      long multiply_accumulate(void *p1, void *p2, int n)
>      {
>        pp1 = p1;
>        pp2 = p2;
>        nn = n;
>        return nn;
>      }
> 
> and then editing in the actual machine instructions one needs, along with
> a human-readable prologue etc. is apt to be much faster than reading through
> all of the documentation to find out everything the development system will
> need.  If one ensures that one saves and restores any registers or CPU state
> that one disturbs, and sets any CPU states upon which one relies, this
> approach should be safe.  Reading the documentation may allow one to avoid
> redundantly saving/restoring state that calling code would never rely upon,
> but if the machine code is either being used to fully encapsulate a time-
> critical loop, or is used to accomplish some non-time-critical task that
> C simply can't do, saving/restoring extra state should be harmless.

This is the method I've played with for tweaking code on the ARM32 where 
I wasn't familiar with the assembly code.

(And also what I had once planned to use to optimise an interpreter for 
ARM32: create a module with a set of 200 functions in C which are 
wrappers around the the byte-code handlers proper in another module.

To start with, each wrapper just calls the regular function. But by 
generating the .s file (compiled with -S, and -O0 to ensure no funny 
business), I can optimise selected functions in the assembly file, and 
do that incrementally to get better performance. I can also try and keep 
essential variables in global registers.

However I never got round to it as I don't use ARM64 enough.)

The important thing though is not to let gcc optimise the code. (Also, 
don't accidentally re-compile the original .c file, as it will wipe out 
any modifications you've made to the .s file!)

-- 
Bartc

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Compile Assembly and C files together Ilias Abrams <iliasabrams@gmail.com> - 2018-03-05 08:23 -0800
  Re: Compile Assembly and C files together "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2018-03-06 19:20 +0800
    Re: Compile Assembly and C files together druck <news@druck.org.uk> - 2018-03-06 13:53 +0000
      Re: Compile Assembly and C files together Rob Morley <nospam@ntlworld.com> - 2018-03-06 14:59 +0000
        Re: Compile Assembly and C files together David Brown <david.brown@hesbynett.no> - 2018-03-06 16:35 +0100
          Re: Compile Assembly and C files together supercat@casperkitty.com - 2018-03-06 07:57 -0800
            Re: Compile Assembly and C files together bartc <bc@freeuk.com> - 2018-03-06 16:35 +0000
              Re: Compile Assembly and C files together Jorgen Grahn <grahn+nntp@snipabacken.se> - 2018-03-06 18:15 +0000
                Re: Compile Assembly and C files together bartc <bc@freeuk.com> - 2018-03-06 18:51 +0000
                Re: Compile Assembly and C files together Jorgen Grahn <grahn+nntp@snipabacken.se> - 2018-03-06 19:22 +0000
                Re: Compile Assembly and C files together bartc <bc@freeuk.com> - 2018-03-06 19:30 +0000
                Re: Compile Assembly and C files together supercat@casperkitty.com - 2018-03-06 12:31 -0800
                Re: Compile Assembly and C files together scott@slp53.sl.home (Scott Lurndal) - 2018-03-06 23:05 +0000
                Re: Compile Assembly and C files together David Brown <david.brown@hesbynett.no> - 2018-03-07 12:17 +0100
                Re: Compile Assembly and C files together Jorgen Grahn <grahn+nntp@snipabacken.se> - 2018-03-07 16:05 +0000
                Re: Compile Assembly and C files together bartc <bc@freeuk.com> - 2018-03-07 16:45 +0000
                Re: Compile Assembly and C files together David Brown <david.brown@hesbynett.no> - 2018-03-07 17:54 +0100
                Re: Compile Assembly and C files together Jorgen Grahn <grahn+nntp@snipabacken.se> - 2018-03-07 16:59 +0000
                Re: Compile Assembly and C files together bartc <bc@freeuk.com> - 2018-03-07 17:13 +0000
              Re: Compile Assembly and C files together David Brown <david.brown@hesbynett.no> - 2018-03-07 12:26 +0100
                Re: Compile Assembly and C files together bartc <bc@freeuk.com> - 2018-03-07 14:25 +0000
                Re: Compile Assembly and C files together David Brown <david.brown@hesbynett.no> - 2018-03-07 15:57 +0100
                Re: Compile Assembly and C files together scott@slp53.sl.home (Scott Lurndal) - 2018-03-07 15:24 +0000
                Re: Compile Assembly and C files together David Brown <david.brown@hesbynett.no> - 2018-03-07 17:56 +0100
            Re: Compile Assembly and C files together David Brown <david.brown@hesbynett.no> - 2018-03-07 11:37 +0100
              Re: Compile Assembly and C files together bartc <bc@freeuk.com> - 2018-03-07 13:11 +0000
                Re: Compile Assembly and C files together David Brown <david.brown@hesbynett.no> - 2018-03-07 15:47 +0100
                Re: Compile Assembly and C files together Malcolm McLean <malcolm.arthur.mclean@gmail.com> - 2018-03-07 07:31 -0800
                Re: Compile Assembly and C files together bartc <bc@freeuk.com> - 2018-03-07 21:00 +0000
                Re: Compile Assembly and C files together David Brown <david.brown@hesbynett.no> - 2018-03-08 12:33 +0100
                Re: Compile Assembly and C files together bartc <bc@freeuk.com> - 2018-03-08 13:05 +0000
                Re: Compile Assembly and C files together David Brown <david.brown@hesbynett.no> - 2018-03-08 15:14 +0100
                Re: Compile Assembly and C files together bartc <bc@freeuk.com> - 2018-03-08 15:23 +0000
                Re: Compile Assembly and C files together David Brown <david.brown@hesbynett.no> - 2018-03-08 23:22 +0100
                Re: Compile Assembly and C files together supercat@casperkitty.com - 2018-03-08 14:40 -0800
                Re: Compile Assembly and C files together Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-03-08 23:59 +0000
                Re: Compile Assembly and C files together supercat@casperkitty.com - 2018-03-08 16:54 -0800
                Re: Compile Assembly and C files together David Brown <david.brown@hesbynett.no> - 2018-03-09 10:37 +0100
                Re: Compile Assembly and C files together Ben Bacarisse <ben.usenet@bsb.me.uk> - 2018-03-09 10:47 +0000
                Re: Compile Assembly and C files together supercat@casperkitty.com - 2018-03-09 09:19 -0800
                Re: Compile Assembly and C files together David Brown <david.brown@hesbynett.no> - 2018-03-09 10:23 +0100
                Re: Compile Assembly and C files together bartc <bc@freeuk.com> - 2018-03-09 12:28 +0000
                Re: Compile Assembly and C files together David Brown <david.brown@hesbynett.no> - 2018-03-09 16:43 +0100
                Re: Compile Assembly and C files together bartc <bc@freeuk.com> - 2018-03-09 17:14 +0000
                Re: Compile Assembly and C files together supercat@casperkitty.com - 2018-03-09 09:32 -0800
                Re: Compile Assembly and C files together scott@slp53.sl.home (Scott Lurndal) - 2018-03-08 15:26 +0000
                Re: Compile Assembly and C files together Jorgen Grahn <grahn+nntp@snipabacken.se> - 2018-03-08 19:23 +0000
                Re: Compile Assembly and C files together David Brown <david.brown@hesbynett.no> - 2018-03-08 23:27 +0100
                Re: Compile Assembly and C files together bartc <bc@freeuk.com> - 2018-03-08 16:17 +0000
                Re: Compile Assembly and C files together David Brown <david.brown@hesbynett.no> - 2018-03-08 23:47 +0100
                Re: Compile Assembly and C files together bartc <bc@freeuk.com> - 2018-03-09 11:59 +0000
              Re: Compile Assembly and C files together supercat@casperkitty.com - 2018-03-07 09:13 -0800
                Re: Compile Assembly and C files together scott@slp53.sl.home (Scott Lurndal) - 2018-03-07 17:42 +0000
                Re: Compile Assembly and C files together supercat@casperkitty.com - 2018-03-07 10:55 -0800
      Re: Compile Assembly and C files together "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2018-03-06 23:01 +0800
    Re: Compile Assembly and C files together ray carter <ray@zianet.com> - 2018-03-06 15:44 +0000
      Re: Compile Assembly and C files together "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2018-03-07 00:07 +0800
        Re: Compile Assembly and C files together Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2018-03-07 22:39 +0200
          Re: Compile Assembly and C files together "Mr. Man-wai Chang" <toylet.toylet@gmail.com> - 2018-03-08 18:18 +0800
            Re: Compile Assembly and C files together Martin Gregorie <martin@mydomain.invalid> - 2018-03-08 12:37 +0000
              Re: Compile Assembly and C files together Martin Gregorie <martin@mydomain.invalid> - 2018-03-08 13:13 +0000
                Re: Compile Assembly and C files together The Natural Philosopher <tnp@invalid.invalid> - 2018-03-08 13:34 +0000
                Re: Compile Assembly and C files together Martin Gregorie <martin@mydomain.invalid> - 2018-03-08 15:27 +0000
                Re: Compile Assembly and C files together mm0fmf <none@invalid.com> - 2018-03-08 17:33 +0000
                Re: Compile Assembly and C files together The Natural Philosopher <tnp@invalid.invalid> - 2018-03-09 09:06 +0000
                Re: Compile Assembly and C files together Richard Kettlewell <invalid@invalid.invalid> - 2018-03-09 09:17 +0000
                Re: Compile Assembly and C files together The Natural Philosopher <tnp@invalid.invalid> - 2018-03-09 09:30 +0000
                Re: Compile Assembly and C files together Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2018-03-09 15:56 +0200
                Re: Compile Assembly and C files together bartc <bc@freeuk.com> - 2018-03-09 14:13 +0000
                Re: Compile Assembly and C files together Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2018-03-09 11:14 -0500
                Re: Compile Assembly and C files together The Natural Philosopher <tnp@invalid.invalid> - 2018-03-09 17:44 +0000
                Re: Compile Assembly and C files together David Brown <david.brown@hesbynett.no> - 2018-03-09 17:16 +0100
                Re: Compile Assembly and C files together Robert Wessel <robertwessel2@yahoo.com> - 2018-03-09 11:19 -0600
                Re: Compile Assembly and C files together bartc <bc@freeuk.com> - 2018-03-09 18:11 +0000
                Re: Compile Assembly and C files together Robert Wessel <robertwessel2@yahoo.com> - 2018-03-09 13:41 -0600
                Re: Compile Assembly and C files together supercat@casperkitty.com - 2018-03-09 10:12 -0800
                Re: Compile Assembly and C files together David Brown <david.brown@hesbynett.no> - 2018-03-09 19:20 +0100
                Re: Compile Assembly and C files together supercat@casperkitty.com - 2018-03-09 11:45 -0800
                Re: Compile Assembly and C files together Robert Wessel <robertwessel2@yahoo.com> - 2018-03-09 13:48 -0600
                Re: Compile Assembly and C files together Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2018-03-09 13:16 -0500
                Re: Compile Assembly and C files together scott@slp53.sl.home (Scott Lurndal) - 2018-03-09 18:29 +0000
                Re: Compile Assembly and C files together Jack Fearnley <jack@alcor.concordia.ca> - 2018-03-09 19:07 +0000
                Re: Compile Assembly and C files together scott@slp53.sl.home (Scott Lurndal) - 2018-03-09 19:13 +0000
                Re: Compile Assembly and C files together Michael J. Mahon <mjmahon@aol.com> - 2018-03-10 13:16 -0600
                Re: Compile Assembly and C files together Martin Gregorie <martin@mydomain.invalid> - 2018-03-11 19:39 +0000
                Re: Compile Assembly and C files together Michael J. Mahon <mjmahon@aol.com> - 2018-03-12 01:16 -0500
                Re: Compile Assembly and C files together Martin Gregorie <martin@mydomain.invalid> - 2018-03-12 20:49 +0000
                Re: Compile Assembly and C files together scott@slp53.sl.home (Scott Lurndal) - 2018-03-12 16:11 +0000
                Re: Compile Assembly and C files together Michael J. Mahon <mjmahon@aol.com> - 2018-03-12 14:58 -0500
                Re: Compile Assembly and C files together scott@slp53.sl.home (Scott Lurndal) - 2018-03-12 20:38 +0000
                Re: Compile Assembly and C files together scott@slp53.sl.home (Scott Lurndal) - 2018-03-12 16:06 +0000
                Re: Compile Assembly and C files together Michael J. Mahon <mjmahon@aol.com> - 2018-03-12 14:58 -0500
                Re: Compile Assembly and C files together Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2018-03-09 21:27 +0200
                Re: Compile Assembly and C files together The Natural Philosopher <tnp@invalid.invalid> - 2018-03-09 17:40 +0000
                Re: Compile Assembly and C files together Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2018-03-09 21:30 +0200
                Re: Compile Assembly and C files together Richard Damon <Richard@Damon-Family.org> - 2018-03-09 13:16 -0500
                Re: Compile Assembly and C files together Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2018-03-09 21:33 +0200
                Re: Compile Assembly and C files together mm0fmf <none@invalid.com> - 2018-03-09 17:40 +0000
                Re: Compile Assembly and C files together The Natural Philosopher <tnp@invalid.invalid> - 2018-03-09 17:47 +0000
                Re: Compile Assembly and C files together mm0fmf <none@invalid.com> - 2018-03-09 18:05 +0000
                Re: Compile Assembly and C files together The Natural Philosopher <tnp@invalid.invalid> - 2018-03-09 09:05 +0000
                Re: Compile Assembly and C files together Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2018-03-09 16:01 +0200
            Re: Compile Assembly and C files together Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2018-03-08 17:25 +0200
    Re: Compile Assembly and C files together The Natural Philosopher <tnp@invalid.invalid> - 2018-03-07 07:36 +0000
  Re: Compile Assembly and C files together Richard Kettlewell <invalid@invalid.invalid> - 2018-03-06 15:29 +0000
    Re: Compile Assembly and C files together David Brown <david.brown@hesbynett.no> - 2018-03-06 16:38 +0100

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