Confusing Mercurial history - was: Re: Hotspot segfaulting on Linux SPARC (original) (raw)

Stefan Karlsson stefan.karlsson at oracle.com
Tue Apr 17 09:34:01 UTC 2018

On 2018-04-17 11:14, John Paul Adrian Glaubitz wrote:

Hi Roman!

On 04/16/2018 08:36 PM, Roman Kennke wrote:

I would normally expect a changeset that was checked in in July to be included in a revision that was checked in in August. I don't understand how one is supposed to perform bi-secting with Mercurial if something as basic as a working history doesn't work in Mercurial.

You're probably wrongly assuming that commit history is linear. It is not. TBH, I don't really know how hg bisect works with branchy history. It usually works fairly well in my experience. It will probably get confused if you start out with two revision on different branches? Or are you trying to bisect manually? Yes, I am aware that the commit history is not linear. However, I am quite sure that the revision 46931 previously contained the revisions 46667 and 46668 in the past but now it doesn't which is what confuses me.

As I Severin said, these numbers are your local numbers and might not at all match what I have in my copy of jdk/hs. However, if we assume that they are the same, I get this:

hg log -r 'reverse(0::46931)' --graph

o changeset: 46931:6e1b59330482 | parent: 46253:f7daf2e39cc8 | user: glaubitz | date: Mon Aug 21 15:17:21 2017 +0200 | summary: 8186433: Compiler flag -arch=sparc should not be passed on linux-sparc |o changeset: 46253:f7daf2e39cc8 | parent: 46250:3041c580db2a | user: bobv | date: Mon Aug 21 12:08:03 2017 -0400 | summary: 8186115: libelf still referenced after 8172670

Where the parent of 46931 is 46253.

And hg log -r '46668::46931'

gives back nothing indicating that 46668 is not a ancestor of 46931.

You can also find the first common ancestor of the two change sets:

hg log -r 'ancestor(46667,46931)' changeset: 45825:4fa7bd62eb84 parent: 45761:9ef5029b247b user: alanb date: Wed Jul 05 13:25:45 2017 +0100 summary: 8183503: Update hotspot tests to allow for unique test classes directory

Can you share the SHA number for your 46668 change, and maybe the summry line as well?

StefanK

Here's some information around this stuff: http://hgbook.red-bean.com/read/finding-and-fixing-mistakes.html#sec:undo:bisect

I have found this guide as well and followed through it. However, in order to start bisecting, I need to find a good revision first which is already where I failed. I tried many different revisions around 46931. But those either contained the bug I am now seeing or they were missing various other changes which are necessary to fix the build on linux-sparc. I have successfully bisected large codebases like QEMU with git in the past successfully but I am completely failing at that with Mercurial. I think I will try a git mirror of the OpenJDK repository next because I am not sure whether I am just using Mercurial wrong or whether bisecting there is so much more difficult as compared to git. For what is worth, I have also tried older versions of binutils and the kernel to make sure that the crash that I am seeing on linux-sparc is just not an artifact. Adrian

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