[Bug 111167] New: Dividing zero by a uniform in loop header causes segfault in nv50_ir::NVC0LegalizeSSA::handleDIV - bugzilla-daemon-CC+yJ3UmIYqDUpFQwHEjaQ

From: bugzilla-daemon-CC+yJ3UmIYqDUpFQwHEjaQ@public.gmane.org
To: nouveau-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org
Subject: [Bug 111167] New: Dividing zero by a uniform in loop header causes segfault in nv50_ir::NVC0LegalizeSSA::handleDIV
Date: Thu, 18 Jul 2019 15:38:38 +0000	[thread overview]
Message-ID: <bug-111167-8800@http.bugs.freedesktop.org/> (raw)

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https://bugs.freedesktop.org/show_bug.cgi?id=111167

            Bug ID: 111167
           Summary: Dividing zero by a uniform in loop header causes
                    segfault in nv50_ir::NVC0LegalizeSSA::handleDIV
           Product: Mesa
           Version: git
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: minor
          Priority: medium
         Component: Drivers/DRI/nouveau
          Assignee: nouveau-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org
          Reporter: abelbriggs1-PkbjNfxxIARBDgjK7y7TUQ@public.gmane.org
        QA Contact: nouveau-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org

Created attachment 144815
  --> https://bugs.freedesktop.org/attachment.cgi?id=144815&action=edit
Reproduction shader_test file, core dump of crash

The attached archive contains a shader that, on the build and PC specified
below, causes a segmentation fault in nouveau when run. A core dump of the
crash is supplied as well.

void main()
{
  for(int i = 1; 1 >= (0 / int((injectionSwitch.y))); 1)
  {
  }
}

The value of injectionSwitch is set to (0.0, 1.0) - so (0 /
int(injectionSwitch.y)) is equivalent to (0 / 1), which should evaluate to zero
and make the two conditions equal. Notably, if you remove injectionSwitch and
replace it with ‘1’, no segfault occurs.

Steps to reproduce:
-------------------------------------------------------------------------------
1. Obtain and build piglit, the Mesa OpenGL test suite runner: 
   https://gitlab.freedesktop.org/mesa/piglit
2. Download the attached archive.
3. From a terminal, execute the supplied test with the piglit GLES3 shader 
   runner: 
   $ bin/shader_runner_gles3 minimum_testcase.shader_test

Expected results:
-------------------------------------------------------------------------------
The shader should run without crashing (it’s an infinite loop that does
nothing, but it still shouldn’t crash).

Actual results:
-------------------------------------------------------------------------------
The shader causes nouveau to segfault.

Here is a backtrace obtained from using GDB on the core dump 
(exact command: $ gdb shader_runner_gles3 core):

#0  std::_Deque_iterator<nv50_ir::ValueRef, nv50_ir::ValueRef&,
nv50_ir::ValueRef*>::_Deque_iterator (
    __x=<error reading variable: Cannot access memory at address 0xb0>, 
    this=<synthetic pointer>) at /usr/include/c++/8/bits/stl_deque.h:1401
#1  std::_Deque_iterator<nv50_ir::ValueRef, nv50_ir::ValueRef&,
nv50_ir::ValueRef*>::operator+ (__n=0, this=0xb0) at
/usr/include/c++/8/bits/stl_deque.h:230
#2  std::_Deque_iterator<nv50_ir::ValueRef, nv50_ir::ValueRef&,
nv50_ir::ValueRef*>::operator[] (__n=0, this=0xb0) at
/usr/include/c++/8/bits/stl_deque.h:247
#3  std::deque<nv50_ir::ValueRef, std::allocator<nv50_ir::ValueRef>
>::operator[] (__n=0, this=0xa0) at /usr/include/c++/8/bits/stl_deque.h:1404
#4  nv50_ir::Instruction::getSrc (s=0, this=0x0)
    at ../src/gallium/drivers/nouveau/codegen/nv50_ir.h:827
#5  nv50_ir::NVC0LegalizeSSA::handleDIV (this=0x7ffd7753af60, i=0x55d2e1b132a0)
    at ../src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp:54
#6  0x00007fc7191cb4b3 in nv50_ir::NVC0LegalizeSSA::visit (
    this=0x7ffd7753af60, bb=<optimized out>)
    at ../src/gallium/drivers/nouveau/codegen/nv50_ir_lowering_nvc0.cpp:334
#7  0x00007fc719111928 in nv50_ir::Pass::doRun (this=0x7ffd7753af60, 
    func=<optimized out>, ordered=<optimized out>, skipPhi=true)
    at ../src/gallium/drivers/nouveau/codegen/nv50_ir_bb.cpp:500
#8  0x00007fc7191119f4 in nv50_ir::Pass::doRun (this=0x7ffd7753af60, 
    prog=<optimized out>, ordered=false, skipPhi=true)
    at ../src/gallium/drivers/nouveau/codegen/nv50_ir_inlines.h:413

Build & PC specs:
-------------------------------------------------------------------------------
CPU: Intel Core i7-5820k 
GPU: nVIDIA GTX 970

OS: Ubuntu 19.04
libdrm: git-5db0f7692d1fdf05f9f6c0c02ffa5a5f4379c1f3
Mesa: git-a110a8090d
Xf86-video-nouveau: 1.0.16
Linux kernel version: 5.0.0-16-generic

This bug was found with GraphicsFuzz: https://github.com/google/graphicsfuzz

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