Re: [PATCH 2/2] [PowerPC Book3E] Introduce new ptrace debug feature flag
From: David Gibson <hidden>
Date: 2011-08-26 04:45:51
On Wed, Aug 24, 2011 at 09:41:43PM -0300, Thiago Jung Bauermann wrote:
On Wed, 2011-08-24 at 14:00 +1000, David Gibson wrote:quoted
On Tue, Aug 23, 2011 at 02:57:56PM +0530, K.Prasad wrote:quoted
On Tue, Aug 23, 2011 at 03:09:31PM +1000, David Gibson wrote:quoted
On Fri, Aug 19, 2011 at 01:23:38PM +0530, K.Prasad wrote:quoted
While PPC_PTRACE_SETHWDEBUG ptrace flag in PowerPC accepts PPC_BREAKPOINT_MODE_EXACT mode of breakpoint, the same is not intimated to the user-space debuggers (like GDB) who may want to use it. Hence we introduce a new PPC_DEBUG_FEATURE_DATA_BP_EXACT flag which will be populated on the "features" member of "struct ppc_debug_info" to advertise support for the same on Book3E PowerPC processors.I thought the idea was that the BP_EXACT mode was the default - if the new interface was supported at all, then BP_EXACT was always supported. So, why do you need a new flag?Yes, BP_EXACT was always supported but not advertised through PPC_PTRACE_GETHWDBGINFO. We're now doing that.I can see that. But you haven't answered why.BookS doesn't support BP_EXACT, that's why I suggested this flag.
Surely you can support it with exactly the same sort of filtering you're using for the 8-byte ranges now?
A BP_EXACT watchpoint triggers only when there's a memory access exactly at the given address. It doesn't trigger when there's (for example) a 4-byte write at an address immediately before which also changes the memory contents of the byte watched by the BP_EXACT watchpoint. a ranged watchpoint would trigger, so the semantics are different. As a general rule, GDB only sets ranged watchpoints and only uses BP_EXACT ones when the user sets a flag. I want GDB to fail when the user sets the flag on BookS since it can't provide the feature.
-- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson