Messages in this thread | | | Date | Thu, 20 Oct 2022 19:00:56 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 1/1] perf arm64: Send pointer auth masks to ring buffer |
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On Thu, Oct 20, 2022 at 06:49:17PM +0200, Peter Zijlstra wrote: > On Thu, Oct 20, 2022 at 11:19:20AM +0100, James Clark wrote: > > From: Andrew Kilroy <andrew.kilroy@arm.com> > > > > Perf report cannot produce callgraphs using dwarf on arm64 where pointer > > authentication is enabled. This is because libunwind and libdw cannot > > unmangle instruction pointers that have a pointer authentication code > > (PAC) embedded in them. > > > > libunwind and libdw need to be given an instruction mask which they can > > use to arrive at the correct return address that does not contain the > > PAC. > > > > The bits in the return address that contain the PAC can differ by > > process, so this patch adds a new sample field PERF_SAMPLE_ARCH_1 > > to allow the kernel to send the masks up to userspace perf. > > > > This field can be used in a architecture specific fashion, but on > > arm64, it contains the ptrauth mask information. The event will > > currently fail to open on architectures other than arm64 if > > PERF_SAMPLE_ARCH_1 is set. It will also fail to open on arm64 if > > CONFIG_ARM64_PTR_AUTH isn't set, as the data would always be zeros. > > A little more information please; wth is pointer authentication? Are we
Mark got me: https://events.static.linuxfound.org/sites/events/files/slides/slides_23.pdf
> going to be having the same thing with x86 LAM where only a subset of > the available bits have meaning to the hardware? > > Why do we want the same mask repeated over and over with each sample; > should this not be part of the address space (side-band) data?
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