From mboxrd@z Thu Jan 1 00:00:00 1970 From: oleg@redhat.com (Oleg Nesterov) Date: Sun, 21 Oct 2012 21:40:58 +0200 Subject: [PATCH 3/9] uprobes: allow ignoring of probe hits In-Reply-To: <20121021181504.GA4840@ubuntu> References: <1350242593-17761-1-git-send-email-rabin@rab.in> <1350242593-17761-3-git-send-email-rabin@rab.in> <20121015165218.GA10239@redhat.com> <20121017173510.GA11019@redhat.com> <20121021181504.GA4840@ubuntu> Message-ID: <20121021194058.GA29137@redhat.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 10/21, Rabin Vincent wrote: > > On Wed, Oct 17, 2012 at 07:35:10PM +0200, Oleg Nesterov wrote: > > > > And, to clarify, I am not arguing. Just curious. > > > > So, is this like cmov on x86? And this patch allows to not report if > > the condition is not true? Or there are other issues on arm? > > Yes, I guess this is like CMOV on x86. In the ARM instruction set most > instructions can be conditionally executed. > > In order to set the probe on a conditional instruction, we use an > undefined instruction with the same condition as the instruction we > replace. However, it is implementation defined whether an undefined > instruction with a failing condition code will trigger an undefined > instruction exception or just be executed as a NOP. So for those > processor implementations where we do get the undefined instruction > exception even for a failing condition code, we have to ignore it in > order to provide consistent behaviour. OK, I see, thanks for your explanation. Oleg.