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Date: | Fri, 10 Mar 2017 00:08:13 -0800 (PST) |
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Subject: | Re: BUG: djgpp should allow 16-byte alignment |
From: | "jwjagersma AT gmail DOT com [via djgpp AT delorie DOT com]" <djgpp AT delorie DOT com> |
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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.
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