Segmentation violation using h2root with 6.40.04

graham · September 22, 2026, 6:41pm

Please fill also the fields below. Note that root -b -q will tell you this info, and starting from 6.28/06 upwards, you can call .forum bug from the ROOT prompt to pre-populate a topic.

ROOT Version: 6.40.04
Platform: lxplus Linux lxplus960.cern.ch 5.14.0-687.39.1.el9_8.x86_64 #1 SMP PREEMPT_DYNAMIC Tue Aug 11 21:20:33 EDT 2026 x86_64 x86_64 x86_64 GNU/Linux
Compiler: Code not compiled by me.

h2root often has a segmentation violation when trying to convert a HBOOK file to a ROOT file with 6.40.04.
This is not seen with 6.40.02 with the same file. The error does not occur on every invocation - but about 50% of the time.

It looks like I’m not currently allowed to upload files at least with this account. Please allow me to
do this as soon as possible (you can ask Rene if I should be trusted …).

I’ve put files that reproduce the problem on my public afs space at CERN.
See /afs/cern.ch/user/g/graham/public/BugReport
including file.histo, Buggy.txt, Correct.txt

[graham@lxplus960 BugReport-h2root]$ whereis h2root
h2root: /usr/bin/h2root /usr/share/man/man1/h2root.1.gz

root --version
ROOT Version: 6.40.04
Built for linuxx8664gcc on Aug 29 2026, 00:00:00
From tags/6-40-04@6-40-04

(I also reproduced the error with 6.40.04 on Ubuntu 24 LTS but found
that 6.40.02 on Ubuntu 24 LTS always worked (ie. I didn’t demonstrate the latter on lxplus).)

Wile_E_Coyote · September 23, 2026, 12:13pm

The offending commit (the “INTEGER*8” breaks it):

github.com/root-project/root

[minicern] Move address computation to 64 bit.

committed 03:54PM - 23 Jun 26 UTC

hageboeck

+7 -0

kernlib was using the LOCF function to compute distances between common blocks. …It shifts the numbers, but in 32 bits. On 64 bit architectures, this can lead to unreasonable values, and when taking the difference, it's either correct or wraps around to very large numbers. Due to aslr, the common blocks move around, which can crash the program at init time when the blocks are on different sides of the "wrap around" addresss. Here, the LOCF function is changed to use 64 bit integers for the address, which makes the distance computation independent of where the kernel places the common blocks. Fix #19329 (cherry picked from commit 0d8fe6621566b21fe910779e6d2b9eedda90fefd) (cherry picked from commit 074b789fb98afb6acd17cad1b09180e64858838b)

@StephanH Note: the “PAWC” and other commons need to be allocated/loaded in the (lowest) 32 bit address space (also, the “-no-pie” flag is needed when building utilities, and often the “-fno-automatic” for the Fortran code, too).

@graham For the time being … download the “official” 6.40.02 binary release for your system, extract the “root/bin/g2root” and “root/bin/h2root” executables, and put them somewhere in your “PATH” (or simply overwrite the executables that came with your 6.40.04 binaries).

graham · September 24, 2026, 4:02pm

Thanks for looking into this. I implemented the workaround also on lxplus, and got that to work (I personally already had the same working solution of reverting to 6.40.02 on Ubuntu).
Maybe this is something that would benefit from a unit test going forward especially with the renewed interest in legacy workflows. Thanks again.

ferhue · October 6, 2026, 2:10pm

Thanks for the report, I opened regression in h2root · Issue #23628 · root-project/root · GitHub