Bug #19456: Incorrect line numbers in GC hook

• Status: Closed
• Assignee: -
• Target version: -
• Backport: 2.7: REQUIRED, 3.0: REQUIRED, 3.1: REQUIRED, 3.2: REQUIRED

[peterzhu2118 (Peter Zhu)]

GitHub PR: https://github.com/ruby/ruby/pull/7357

If the previous instruction is not a leaf instruction, then the PC was incremented before the instruction was ran (meaning the currently executing instruction is actually the previous instruction), so we should not increment the PC otherwise we will calculate the source line for the next instruction.

This bug can be reproduced in the following script:

require "objspace"

ObjectSpace.trace_object_allocations_start
a =





  1.0 / 0.0
p [ObjectSpace.allocation_sourceline(a), ObjectSpace.allocation_sourcefile(a)]

Which outputs: [4, "test.rb"]

This is incorrect because the object was allocated on line 10 and not line 4. The behaviour is correct when we use a leaf instruction (e.g. if we replaced 1.0 / 0.0 with "hello"), then the output is: [10, "test.rb"].

[peterzhu2118 (Peter Zhu)]

• Status changed from Open to Closed

Applied in changeset git|3e098224077e8c43a1d8c2070b26ffdfda422780.

---

Fix incorrect line numbers in GC hook

If the previous instruction is not a leaf instruction, then the PC was
incremented before the instruction was ran (meaning the currently
executing instruction is actually the previous instruction), so we
should not increment the PC otherwise we will calculate the source
line for the next instruction.

This bug can be reproduced in the following script:

require "objspace"

ObjectSpace.trace_object_allocations_start
a =

  1.0 / 0.0
p [ObjectSpace.allocation_sourceline(a), ObjectSpace.allocation_sourcefile(a)]

Which outputs: [4, "test.rb"]

This is incorrect because the object was allocated on line 10 and not
line 4. The behaviour is correct when we use a leaf instruction (e.g.
if we replaced 1.0 / 0.0 with "hello"), then the output is:
[10, "test.rb"].

[Bug #19456]