On June 22, 2021 4:33:09 PM GMT+02:00, Qing Zhao <qing.z...@oracle.com> wrote: > > >> On Jun 22, 2021, at 9:15 AM, Richard Biener <rguent...@suse.de> >wrote: >> >> On Tue, 22 Jun 2021, Qing Zhao wrote: >> >>> >>> >>>> On Jun 22, 2021, at 9:00 AM, Richard Biener <rguent...@suse.de> >wrote: >>>> >>>> On Tue, 22 Jun 2021, Qing Zhao wrote: >>>> >>>>> So, I am wondering why not still keep my current implementation on > >>>>> assign different patterns for different types? >>>>> >>>>> This major issue with this design is the code size and runtime >overhead, >>>>> but for debugging purpose, those are not that important, right? >And we >>>>> can add some optimization later to improve the code size and >runtime >>>>> overhead. >>>>> >>>>> Otherwise, if we only use one pattern for all the types in this >initial >>>>> version, later we still might need change it. >>>>> >>>>> How do you think? >>>> >>>> No, let's not re-open that discussion. As said we can look to >support >>>> multi-byte pattern if that has a chance to improve things but only >>>> as followup. >>> >>> I am fine with this. >>> >>> However, we need to decide whether we will use one-byte repeatable >pattern, or multiple-byte repeatable pattern now, >>> Since the implementation will be different. If using one-byte, the >implementation will be the simplest, we can use memset for all >>> VLA, non-vla, zero-init, or pattern-init consistently. >>> >>> However, if we choose multiple-byte pattern, then the implementation >will be different, we cannot use memset for pattern-init, and >>> The implemenation for VLA pattern-init also is different. >> >> As said, we can do this as followup. For now get the easiest thing >> working - one-byte patterns via memset. > >Okay. I will work on this. > >> There's enough bits in the >> patch that will likely need followup fixes (the .DEFERED_INIT stuff), > >Do you mean your previous suggestion to merge the handling of VLA to >non-VLA during gimplification phase? >I have done with this change locally.
No, just bugs that will inevitably show up. >> actual code gneration of the init is separate enough we can deal with >> it later. Also IMHO not all targets necessarily need to behave the >> same there. > >Then, shall we make the code generation part a target hook now? Or do >this later? Do this later, if the need arises. Richard. >Qing >> >> Richard. >> >>> Qing >>>> >>>> Thanks, >>>> Richard. >>>> >>>>> Qing >>>>> >>>>> On Jun 22, 2021, at 3:59 AM, Richard Biener ><rguent...@suse.de<mailto:rguent...@suse.de>> wrote: >>>>> >>>>> On Tue, 22 Jun 2021, Richard Sandiford wrote: >>>>> >>>>> Kees Cook <keesc...@chromium.org<mailto:keesc...@chromium.org>> >writes: >>>>> On Mon, Jun 21, 2021 at 03:39:45PM +0000, Qing Zhao wrote: >>>>> So, if “pattern value” is “0xFFFFFFFFFFFFFFFF”, then it’s a valid >canonical virtual memory address. However, for most OS, >“0xFFFFFFFFFFFFFFFF” should be not in user space. >>>>> >>>>> My question is, is “0xFFFFFFFFFFFFFFFFF” good for pointer? Or >“0xAAAAAAAAAAAAAAAA” better? >>>>> >>>>> I think 0xFF repeating is fine for this version. Everything else >is a >>>>> "nice to have" for the pattern-init, IMO. :) >>>>> >>>>> Sorry to be awkward, but 0xFF seems worse than 0xAA to me. >>>>> >>>>> For integer types, all values are valid representations, and we're >>>>> relying on the pattern being “obviously” wrong in context. >0xAAAA… >>>>> is unlikely to be a correct integer but 0xFFFF… would instead be a >>>>> “nice” -1. It would be difficult to tell in a debugger that a -1 >>>>> came from pattern init rather than a deliberate choice. >>>>> >>>>> I agree that, all other things being equal, it would be nice to >use NaNs >>>>> for floats. But relying on wrong numerical values for floats >doesn't >>>>> seem worse than doing that for integers. >>>>> >>>>> 0xAA… for float is (if I've got this right) >-3.0316488252093987e-13, >>>>> which admittedly doesn't stand out as wrong. But I'm not sure we >>>>> should sacrifice integer debugging for float debugging here. >>>>> >>>>> We can always expose the actual value as --param. Now, I think >>>>> we'd need a two-byte pattern to reliably produce NaNs anyway, >>>>> so with floats taken out of the picture the focus should be on >>>>> pointers where IMHO val & 1 and val & 15 would be nice to have. >>>>> So sth like 0xf7 would work for those. With a two-byte pattern >>>>> we could use 0xffef or 0x7fef. >>>>> >>>>> Anyway, it's probably down to priorities of the project involved >>>>> (debugging FP stuff or integer stuff). >>>>> >>>>> Richard. >>>>> >>>>> >>>> >>>> -- >>>> Richard Biener <rguent...@suse.de> >>>> SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 >Nuernberg, >>>> Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg) >>> >>> >> >> -- >> Richard Biener <rguent...@suse.de> >> SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 >Nuernberg, >> Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
