> On May 21, 2018, at 9:51 AM, Alexey Budankov > <alexey.budan...@linux.intel.com> wrote: > > > Hi Andy, >> On 21.05.2018 17:14, Andy Lutomirski wrote: >> >>> On May 21, 2018, at 5:44 AM, Alexey Budankov >>> <alexey.budan...@linux.intel.com> wrote: >>> >>> Hi Peter, >>> >>>> On 10.05.2018 13:14, Peter Zijlstra wrote: >>>> On Thu, May 10, 2018 at 12:42:38PM +0300, Alexey Budankov wrote: >>>>>> The Changelog needs to state that user_regs->bp is in fact valid and >>>>> >>>>> That actually was tested on binaries compiled without and with BP exposed >>>>> and in the latter case proved the value of that change. >>>> >>>> Mostly works is not the same as 'always initialized', if there are entry >>>> paths that do not store that register, then using the value might leak >>>> values from the kernel stack, which would be bad. >>>> >>>> But like said, I think much of the kernel entry code was sanitized with >>>> the PTI effort and I suspect things are in fact fine now, but lets wait >>>> for Andy to confirm. >>> >>> It looks like, these days, all registers are saved on system calls, just >>> like you anticipated. >>> >>> So BP register value might be stored into the Perf trace on a sample. >>> >>> Andy? >> >> Hmm, I thought I replied. Yes, they are indeed all saved, but I’m not very >> excited about committing to doing so forever. But storing BP should be fine. > > Thanks for explicit confirmation regarding BP register. > BTW, do you see any mean to prevent possible unattended regression? > I guess it could be some compile time assertion or regression testing.
Write a selftest? The whole perf user regs mechanism is buggy and fragile. I need to massively clean it up at some point. > > Thanks, > Alexey > >>
