similar to: RFC: XRay -- A Function Call Tracing System

Hi llvm-dev (cc google-xray), As a follow-up to the first XRay RFC [0] introducing the technology, I've been able to recently implement a functional prototype of the major parts of the XRay functionality [1]. This RFC is limited to exploring potential alternatives to the current LLVM-side changes, with the interest of getting clear guidance for landing the changes first in LLVM. Background /

Sorry, I initially included LLVM-Commits rather than LLVM-Dev. Fixed. On 26 January 2017 at 03:26, Serge Rogatch <serge.rogatch at gmail.com> wrote: > Hi Dean, Renato, > > AFAIK, unfortunately, these critical Arm32 XRay fixes are not yet in 4.0: > https://reviews.llvm.org/D28624 , https://reviews.llvm.org/D28623 . The > first repairs XRay instrumentation map emission.

Hi Dean, I have a question for 32-bit platforms. I see in the code that you used the following in compiler-rt/trunk/lib/xray/xray_interface_internal.h : struct XRaySledEntry { uint64_t Address; uint64_t Function; unsigned char Kind; unsigned char AlwaysInstrument; unsigned char Padding[14]; // Need 32 bytes }; And the peer code in llvm/trunk/lib/Target/X86/X86MCInstLower.cpp : void

How is XRay tested? IIRC, Renato didn't see any test failures on ARM? Merging sounds reasonbaly, I'd just like to understand what's the risk for the branch. On Thu, Jan 26, 2017 at 10:29 AM, Serge Rogatch <serge.rogatch at gmail.com> wrote: > Hans, these changes reached trunk in https://reviews.llvm.org/rL292516 and > https://reviews.llvm.org/rL292517 . Could you look?

I'm wondering why the lit tests didn't catch this as part of testing rc1 on ARM. On Thu, Jan 26, 2017 at 11:25 AM, Serge Rogatch <serge.rogatch at gmail.com> wrote: > XRay is tested automatically on build-bots with tests in LLVM and > compiler-rt . Or are you asking for manual testing instructions? > Of these 2 patches, the compiler-rt patch depends on LLVM patch because

I see. Thanks for clarifying. I'm Ok with merging these if Dean agrees, as I believe he's the code owner. Thanks, Hans On Thu, Jan 26, 2017 at 11:47 AM, Serge Rogatch <serge.rogatch at gmail.com> wrote: > There were no LLVM tests for presence of XRay instrumentation map in the > emitted assembly. You can see that https://reviews.llvm.org/D28624 adds this > check to the

Hi llvm-dev, I'm currently looking for alternatives to the synthetic references that XRay uses to keep some side-tables live, to avoid linker garbage collection from deleting those sections. Before going any further, let me give a backgrounder on what XRay does today. Background ========== XRay has two side tables we use at runtime to identify the location of the sleds for the functions

> On 29 Jul 2016, at 09:14, Serge Rogatch via llvm-dev <llvm-dev at lists.llvm.org> wrote: > > Hello, > > Can I ask you why you chose to patch both function entrances and exits, rather than just patching the entrances and (in the patches) pushing on the stack the address of __xray_FunctionExit , so that the user function returns normally (with RETQ or POP RIP or whatever

On 29 July 2016 at 10:43, Dean Michael Berris <dean.berris at gmail.com> wrote: > > > On 29 Jul 2016, at 09:14, Serge Rogatch via llvm-dev < > llvm-dev at lists.llvm.org> wrote: > > > > Hello, > > > > Can I ask you why you chose to patch both function entrances and exits, > rather than just patching the entrances and (in the patches) pushing on

> On 30 Jul 2016, at 05:07, Serge Rogatch via llvm-dev <llvm-dev at lists.llvm.org> wrote: > > Thanks for pointing this out, Tim. Then maybe this approach is not the best choice for x86, though ideally measuring is needed, it is just that on ARM the current x86 approach is not applicable because ARM doesn't have a single return instruction (such as RETQ on x86_64), furthermore,

I think that 32-bit systems (especially ARM) may be short on memory so doubling the size of the table containing (potentially) all the functions may give a tangible overhead. I would even align the entries to 4 bytes (so 12 bytes per entry) on 32-bit platforms and to 8 bytes (so 24-bytes per entry) on 64-bit platforms, to improve CPU cache hits. What do you think? Cheers, Serge On 8 August 2016

Hi, As part of working on XRay, I'm trying to accomplish the following: create a section that contains an array of entries pertaining to the instrumentation map (nop sleds) in an object file, and have those merged into a single section in the final binary where the contents are concatenated. The trick though is I'd like to be able to reference the whole array with a single symbol (or two,

> On 4 Aug 2016, at 06:27, Serge Rogatch <serge.rogatch at gmail.com> wrote: > > Hi Dean, > > I have a question about the following piece of code in compiler-rt/trunk/lib/xray/xray_trampoline_x86.S : > movq _ZN6__xray19XRayPatchedFunctionE(%rip), %rax > testq %rax, %rax > je .Ltmp0 > > // assume that %r10d has the function id. > movl %r10d,

Hello, Can I ask you why you chose to patch both function entrances and exits, rather than just patching the entrances and (in the patches) pushing on the stack the address of __xray_FunctionExit , so that the user function returns normally (with RETQ or POP RIP or whatever else instruction) rather than jumping into __xray_FunctionExit? By patching just the function entrances, you avoid

> On 7 Sep 2016, at 01:21, David Blaikie <dblaikie at gmail.com> wrote: > > (sorry for the delay) > All good, thanks Dave! > On Tue, Aug 23, 2016 at 1:05 AM Dean Michael Berris <dean.berris at gmail.com <mailto:dean.berris at gmail.com>> wrote: > Hi llvm-dev, > > I've been implementing a tool for analysing XRay traces. A recap of XRay's

Thanks for pointing this out, Tim. Then maybe this approach is not the best choice for x86, though ideally measuring is needed, it is just that on ARM the current x86 approach is not applicable because ARM doesn't have a single return instruction (such as RETQ on x86_64), furthermore, the return instructions on ARM can be conditional. I have another question: what happens if the instrumented

Awesome, thanks Peter! Cheers On Thu, Jun 23, 2016 at 10:35 AM Peter Collingbourne <peter at pcc.me.uk> wrote: > If you give your section a valid C identifier name, i.e. something like > "xray_instr_map" (no period), the linker will synthesize symbols named > "__start_xray_instr_map" and "__stop_xray_instr_map", which will point to > the start and

On Tue, May 8, 2018 at 4:06 AM Soham Sinha <soham1 at bu.edu> wrote: > Hello Dean, > I looked at the XRay Instrumentation. That's a nice engineering effort. I am sure you had your motivation to do this in CodeGen just like I wanted to do. I don't understand all of your code but I get the idea that you are adjusting the alignment with explicit bytes and no-op instructions. My

Just to close this out, I've updated http://reviews.llvm.org/D19904 to use named ELF groups per-function, and have the runtime library use __start_xray_instr_map and __stop_xray_instr_map as weak symbols from the C++ side. I've sent a patch to make creating these COMDAT/Group sections easier when lowering through the MCStreamer interface ( http://reviews.llvm.org/D21743). Cheers On Fri,

On Fri, Jun 17, 2016 at 5:42 AM Matthias Braun via llvm-dev < llvm-dev at lists.llvm.org> wrote: > Some of this overlaps with the features in XRay ( > http://lists.llvm.org/pipermail/llvm-dev/2016-April/098901.html). > > Matthias beat me to it! >From reading the RFC, it seems that some of what XRay is doing on the instrumentation side is very similar to what CSI enables. The