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Potomac

Member

Registered: 2011-12-25

Posts: 551

[mesa] crash when mesa is linked to LLVM 3.7.0

Hello,

I have a strange bug since mesa has been upgraded to 11.0.x version and also since llvm and llvm-libs have been upgraded to the 3.7.0 version,

I use the mesa r600 driver ( /usr/lib/xorg/modules/dri/r600_dri.so ), I have a radeon HD4650 pcie, a pentium dual core E6800 ( 3.33 Ghz ), I use archlinux 64 bits,

the bug occurs when a program use the openGL function glRasterPos2i(), or when the 100% emulation software mode is used ( "export LIBGL_ALWAYS_SOFTWARE=1" ),

for example the crash will occur with the program "tunnel" ( from mesa-demos package ), it will crash with the error "illegal instruction",

I want to know if I am alone with this bug ?

I can also reproduce this in a virtual machine ( qemu i686 ),

I created a bugreport :

https://bugs.freedesktop.org/show_bug.cgi?id=92214

if I downgrade to llvm 3.6.2 and llvm-libs 3.6.2, and if I rebuild mesa packages ( in order to link them to llvm-libs 3.6.2 ) then there is no bug, all is ok

Last edited by Potomac (2015-10-13 20:15:09)

Potomac

Member

Registered: 2011-12-25

Posts: 551

Re: [mesa] crash when mesa is linked to LLVM 3.7.0

I made a discovery :

in qemu I can set a type of CPU ( pentium, pentium2, pentium2, core2duo, SandyBridge and many more ), you can see the CPUs list with the command "qemu-i386 -cpu ?",

until now I used the qemu option "-cpu host", which means that it's the CPU of the host who is emulated ( my pentium dual core E6800 ),

then I decided to set a different CPU name in my qemu script :

-cpu core2duo -enable-kvm  -machine type=pc,accel=kvm -smp 2

with this setting the bug disapears, all is ok in my virtual machine, glxgears and all openGL programs can run without crash, the mesa driver llvmpipe doesn't crash,

after that I decided to do set again another CPU in qemu :

-cpu Penryn -enable-kvm  -machine type=pc,accel=kvm -smp 2 \

with "Penryn" CPU the bug is back in my virtual machine, which means that the bug seems related to the type of CPU, llvm 3.7.0 lib may have a bug when he tries to generate binary code, it fails with some CPUs,

this problem doesn't exist with llvm 3.6.2 lib

Lone_Wolf

Administrator

From: Netherlands, Europe

Registered: 2005-10-04

Posts: 14,840

Re: [mesa] crash when mesa is linked to LLVM 3.7.0

Mesa was just updated to 11.0.3 , do the problems also occur with that version ?

---

Disliking systemd intensely, but not satisfied with alternatives so focusing on taming systemd.

clean chroot building not flexible enough ?
Try clean chroot manager by graysky

Potomac

Member

Registered: 2011-12-25

Posts: 551

Re: [mesa] crash when mesa is linked to LLVM 3.7.0

yes the problem is still here with mesa 11.0.3

Potomac

Member

Registered: 2011-12-25

Posts: 551

Re: [mesa] crash when mesa is linked to LLVM 3.7.0

I did further tests,

I found that llvm 3.7.0 sees my CPU pentium dual core like a "Penryn" :

$ llc --version | grep CPU
  Host CPU: penryn

but llvm 3.6.2 ( who doesn't have the bug ) sees my CPU pentium dual core like a "core2"

$ llc --version | grep CPU
  Host CPU: core2

why this different behaviour ?

it could explain this bug if llvm 3.7.0 generates binary code for a wrong cpu ( penryn instead of core 2 )

Last edited by Potomac (2015-10-13 21:33:11)

Potomac

Member

Registered: 2011-12-25

Posts: 551

Re: [mesa] crash when mesa is linked to LLVM 3.7.0

I found the cause of this bug,

it's llvm 3.7.0, the llvm git commit who has introduced this bug is :

cd83d5b5071f072882ad06cc4b904b2d27d1e54a

https://github.com/llvm-mirror/llvm/com … 2d27d1e54a

the problem is that llvm 3.7.0 treats my pentium dual core as a "penryn",

penryn supports SSE4, but not the pentium dual core series ( CPU family 6 model 23 ),

the faulty commit has deleted a test about SSE4 :

return HasSSE41 ? "penryn" : "core2";

the solution is simply to add this test for CPU family 6 model 23, I created a patch who solves this bug :

--- a/lib/Support/Host.cpp    2015-10-14 07:13:52.381374679 +0200
+++ b/lib/Support/Host.cpp   2015-10-14 07:13:28.224708323 +0200
@@ -332,6 +332,8 @@
                // 17h. All processors are manufactured using the 45 nm process.
                //
                // 45nm: Penryn , Wolfdale, Yorkfield (XE)
+        // Not all Penryn processors support SSE 4.1 (such as the Pentium brand)
+        return HasSSE41 ? "penryn" : "core2";          
       case 29: // Intel Xeon processor MP. All processors are manufactured using
                // the 45 nm process.
         return "penryn";

this patch has been sent to llvm's bugzilla, I hope they will accept it

Last edited by Potomac (2015-10-14 06:39:14)