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RE: [Xen-devel] [Fwd: stack overflow "cause" found]

To: "Rik van Riel" <riel@xxxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] [Fwd: stack overflow "cause" found]
From: "Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>
Date: Wed, 26 Jul 2006 22:46:42 +0100
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Thread-topic: [Xen-devel] [Fwd: stack overflow "cause" found]
> > Xen really should not be doing this.  We could either uninline some of
> > these functions, or try gcc -O2 or gcc -Os.
> OK, with -Os it doesn't quite build due to the built-ins not being
> inlined.  With -O2 the stack usage changes dramatically...

It would be nice if -O2 worked. Quite a scary change give the amount of inline 
asm  though...

> > Currently the top stack users are:
> >
> > $ objdump -dS xen-syms | ./checkstack.pl x86_64
> > 0xffff8300001c7c47 find_unisys_acpi_oem_table:          1296
> > 0xffff83000011182e do_xen_version:                      1280
> > 0xffff83000015bc3e x86_emulate_memop:                   1264
> > 0xffff8300001adbaa vmx_world_save:                      1040
> > 0xffff8300001aeac5 vmx_world_save:                      1040
> > 0xffff8300001af923 vmx_assist:                          224
> The function vmx_world_save is inlined into vmx_assist with -O2,
> and the combined stack use is only 200 bytes, down from 1264 !
> I guess we'll want to build Xen with -O2.  I'm testing a -O2 built
> hypervisor right now...
> --
> "Debugging is twice as hard as writing the code in the first place.
> Therefore, if you write the code as cleverly as possible, you are,
> by definition, not smart enough to debug it." - Brian W. Kernighan
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