Date: Thu, 30 Apr 2009 11:01:40 +0200 From: Rafal Jaworowski <raj@semihalf.com> To: Marcel Moolenaar <xcllnt@mac.com> Cc: freebsd-ppc@freebsd.org Subject: Re: Single stepping through atomic ops Message-ID: <F9D995D9-D032-498B-B252-CCED9E1D0540@semihalf.com> In-Reply-To: <36D74D0F-DB5D-4B3D-8A34-2AC72A5209AF@semihalf.com> References: <36D74D0F-DB5D-4B3D-8A34-2AC72A5209AF@semihalf.com>
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On 2009-04-21, at 19:57, Rafal Jaworowski wrote: > Hi Marcel, > I'm writing to you primarily as the gdb maintainer :-) There's a > problem with current gdb in base when single stepping through atomic > sequences on PowerPC (and presumably other archs with the load + > conditional store approach for atomic ops). The effect is a hang > because we endlessly loop due to the [always] lost reservation at > the time of a closing stwcx. > > This is a known problem with gdb and it's fixed with newer versions, > but the patches are not applicable to our gdb due to some > infrastructure changes. The quick fix for 6.1.1 is here: > http://people.freebsd.org/~raj/patches/powerpc/gdb-ppc-single- > step.diff > > It's mainly a transplant of two fixes from the gdb repository > (1.275, 1.276, deal_with_atomic_sequence) adjusted to our older gdb > code, but it's ugly #ifdef'ed __ppc__. In order to do it cleanly we > would need to change the signature of the SOFTWARE_SINGLE_STEP > method so it returns a value (this is how newer gdb works), but it > would affect gdb for all architectures. Do you see any objections > for growing a return value here? > > Another direction would be importing a newer gdb code base, and be > able to apply the fixes directly and cleanly (if at all required), > but am not sure if there are any plans to upgrade gdb in base? Let > me know your comments. Have you got any comments to this? Should I move on and commit this as ugly as is, or would reworking SOFTWARE_SINGLE_STEP be more desired? Any thoughts about newer gdb versions coming to the tree? Rafal
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