Mail Archives: djgpp/2017/03/12/00:15:50
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| From: | "Louis Santillan (lpsantil AT gmail DOT com) [via djgpp AT delorie DOT com]" <djgpp AT delorie DOT com>
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| Date: | Sat, 11 Mar 2017 21:15:39 -0800
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| Message-ID: | <CAB9Rao9rmU8wSxVGYEbkWut8qdc_CtvYX620tA1nEWRbpepe9w@mail.gmail.com>
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| Subject: | Re: BUG: djgpp should allow 16-byte alignment
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--001a11410e909098fb054a81af06
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Have you tried using `-mstackrealign`? That might correct the errors you
are seeing. Without seeing any code, it's hard to say what's going on.
Looking at BZ, I see the code there but no compiler flags.
On Fri, Mar 10, 2017 at 12:08 AM, jwjagersma AT gmail DOT com [via
djgpp AT delorie DOT com] <djgpp AT delorie DOT com> wrote:
> On Friday, 10 March 2017 00:13:25 UTC+1, Louis Santillan (
> lpsantil AT gmail DOT com) [via djgpp AT delorie DOT com] wrote:
> > Are you unable to use `--mstackrealign`, `-mpreferred-stack-boundary=num`,
> `-mincoming-stack-boundary=num` [0]? Looks like you'll also need to
> force those options if you compile with `-Os` as well.
> >
> >
> >
> >
> > [0] https://gcc.gnu.org/onlinedocs/gcc-4.8.5/gcc/i386-
> and-x86-64-Options.html#i386-and-x86-64-Options
> >
> >
> > On Thu, Mar 9, 2017 at 8:14 AM, jwjag DOT DOT DOT AT gmail DOT com [via
> dj DOT DOT DOT AT delorie DOT com] <dj DOT DOT DOT AT delorie DOT com> wrote:
> > Currently it seems that djgpp does not support 16-byte alignment. Since
> djgpp-compiled programs can potentially use SSE instructions (either
> explicitly or implicitly, when compiled with -march=pentium3), I do think
> this should be supported.
> >
> >
> >
> > previous discussion:
> >
> > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79935
>
> I was already using -mpreferred-stack-boundary=4 (which implies
> -mincoming-stack-boundary=4) but that didn't seem to have the intended
> effect. Most notably in static constructors, the stack alignment is always
> 8 bytes off. From the disassembly I can tell gcc does its best to keep the
> stack aligned, so that part works correctly, at least.
>
> Now yesterday I had a problem in a non-static function, where gcc inserted
> an SSE instruction with a memory operand [ebp-0x58], with (ebp % 0x10 ==
> 0x0c). That doesn't make any sense at all! It's guaranteed to cause a GP
> fault and gcc should know this.
>
>
--001a11410e909098fb054a81af06
Content-Type: text/html; charset=UTF-8
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<div dir=3D"ltr">Have you tried using `<span style=3D"color:rgb(0,0,0);font=
-family:monospace;font-size:medium">-mstackrealign`?=C2=A0 That might corre=
ct the errors you are seeing.=C2=A0 Without seeing any code, it's hard =
to say what's going on.=C2=A0 Looking at BZ, I see the code there but n=
o compiler flags.</span></div><div class=3D"gmail_extra"><br><div class=3D"=
gmail_quote">On Fri, Mar 10, 2017 at 12:08 AM, <a href=3D"mailto:jwjagersma=
@gmail.com">jwjagersma AT gmail DOT com</a> [via <a href=3D"mailto:djgpp AT delorie DOT c=
om">djgpp AT delorie DOT com</a>] <span dir=3D"ltr"><<a href=3D"mailto:djgpp AT de=
lorie.com" target=3D"_blank">djgpp AT delorie DOT com</a>></span> wrote:<br><bl=
ockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1px #=
ccc solid;padding-left:1ex"><span class=3D"">On Friday, 10 March 2017 00:13=
:25 UTC+1, Louis Santillan (<a href=3D"mailto:lpsantil AT gmail DOT com">lpsantil@=
gmail.com</a>) [via <a href=3D"mailto:djgpp AT delorie DOT com">djgpp AT delorie DOT com<=
/a>]=C2=A0 wrote:<br>
> Are you unable to use `--mstackrealign`, `-mpreferred-stack-boundary=
=3D<wbr>num`, `-mincoming-stack-boundary=3D<wbr>num` [0]?=C2=A0 Looks like =
you'll also need to force those options if you compile with `-Os` as we=
ll.<br>
><br>
><br>
><br>
><br>
> [0] <a href=3D"https://gcc.gnu.org/onlinedocs/gcc-4.8.5/gcc/i386-and-x=
86-64-Options.html#i386-and-x86-64-Options" rel=3D"noreferrer" target=3D"_b=
lank">https://gcc.gnu.org/<wbr>onlinedocs/gcc-4.8.5/gcc/i386-<wbr>and-x86-6=
4-Options.html#i386-<wbr>and-x86-64-Options</a>=C2=A0=C2=A0<br>
><br>
><br>
</span><span class=3D"">> On Thu, Mar 9, 2017 at 8:14 AM, <a href=3D"mai=
lto:jwjag DOT DOT DOT AT gmail DOT com">jwjag DOT DOT DOT AT gmail DOT com</a> [via <a href=3D"mailto:dj...=
@delorie.com">dj DOT DOT DOT AT delorie DOT com</a>] <<a href=3D"mailto:dj DOT DOT DOT AT delorie DOT co=
m">dj DOT DOT DOT AT delorie DOT com</a>> wrote:<br>
> Currently it seems that djgpp does not support 16-byte alignment. Sinc=
e djgpp-compiled programs can potentially use SSE instructions (either expl=
icitly or implicitly, when compiled with -march=3Dpentium3), I do think thi=
s should be supported.<br>
><br>
><br>
><br>
> previous discussion:<br>
><br>
> > <a href=3D"https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D79935" =
rel=3D"noreferrer" target=3D"_blank">https://gcc.gnu.org/bugzilla/<wbr>show=
_bug.cgi?id=3D79935</a><br>
<br>
</span>I was already using -mpreferred-stack-boundary=3D4 (which implies -m=
incoming-stack-boundary=3D4) but that didn't seem to have the intended =
effect. Most notably in static constructors, the stack alignment is always =
8 bytes off. From the disassembly I can tell gcc does its best to keep the =
stack aligned, so that part works correctly, at least.<br>
<br>
Now yesterday I had a problem in a non-static function, where gcc inserted =
an SSE instruction with a memory operand [ebp-0x58], with (ebp % 0x10 =3D=
=3D 0x0c). That doesn't make any sense at all! It's guaranteed to c=
ause a GP fault and gcc should know this.<br>
<br>
</blockquote></div><br></div>
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