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Re: 16 byte pthread stack alignments
- From: Brian Ford <Brian dot Ford at FlightSafety dot com>
- To: cygwin at cygwin dot com
- Date: Mon, 9 Jan 2012 09:41:07 -0600
- Subject: Re: 16 byte pthread stack alignments
- References: <Pine.CYG.4.58.1112201743030.3964@PC1163-8460-XP.flightsafety.com> <20111221094211.GH23547@calimero.vinschen.de> <4EF1F937.email@example.com> <20111221154104.GB11841@calimero.vinschen.de> <Pine.CYG.4.58.1112211020000.3076@PC1163-8460-XP.flightsafety.com> <20111221165053.GA9699@calimero.vinschen.de> <Pine.CYG.4.58.1112221245050.748@PC1163-8460-XP.flightsafety.com> <20111223135247.GM31936@calimero.vinschen.de> <Pine.CYG.4.58.1112271735200.748@PC1163-8460-XP.flightsafety.com> <20120109141345.GK15470@calimero.vinschen.de>
- Reply-to: cygwin at cygwin dot com
On Mon, 9 Jan 2012, Corinna Vinschen wrote:
> On Dec 27 18:06, Brian Ford wrote:
> > On Fri, 23 Dec 2011, Corinna Vinschen wrote:
> > > Sorry, but what I don't get from your reply is if the andl worked or
> > > not.
> > No; by itself, it does not. Adding a "subl $12, %%esp" following it so
> > that the stack is 16 byte aligned after the thread arg is pushed does
> > work. There are probably more efficient and/or cleaner ways of doing it
> > though.
> > STC attached, but note that it seems to always pass with gcc-4. Only gcc
> > 3.4.4 appears to require the extra alignment.
> Ok, this is even more puzzeling. The thread function called from the
> thread_wrapper function is NOT the application thread function, but the
> Cygwin internal function thread_init_wrapper. Given that this function
> is built with the same gcc 4.x compiler as the rest of Cygwin, how on
> earth can this fail at all? Shouldn't the alignment be always correct on
> the subsequent call to the application function, given that gcc-4 is
> supposed to care?
I'm speculating, but I believe gcc-4 only re-aligns the stack in case an
instruction in that function requires more strict alignment than the
default ABI to save overhead.
Staff Realtime Software Engineer
VITAL - Visual Simulation Systems
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