[Mesa-dev] powerpc / gallium/drivers/llvmpipe segfaults running lp_test_* tests

[Will Schmidt]

Hi, 
  I'm starting to investigate mesa/llvmpipe on powerpc
(powerpc64/power7) and hitting some issues trying to run the tests found
in mesa/src/gallium/drivers/llvmpipe/lp_test_*.   (lp_test_arit,
lp_test_printf, lp_test_blend all seem to fail in similar fashion.
lp_test_round passes, but does not provide any output, so I'm not sure
it's actually doing anything. )

I'll note that I'm still ramping up on my understanding of all the
parts, don't quite know what I'm doing yet, and will not be surprised if
this involves user error.  pointers and tips on what I should
tweak/poke/kick next are appreciated.  :-)


Configure and build are on a fedora 17 based power7 box, using mesa .git
HEAD as of today.  
[willschm at fuzzy mesa]$ ./autogen.sh --enable-gallium-llvm

< build steps trimmed >

[willschm at fuzzy mesa]$ cd src/gallium/drivers/llvmpipe
[willschm at fuzzy llvmpipe]$ ./lp_test_printf
Segmentation fault
[willschm at fuzzy llvmpipe]$ file ./lp_test_printf 
./lp_test_printf: ELF 64-bit MSB executable, 64-bit PowerPC or cisco
7500, version 1 (GNU/Linux), dynamically linked (uses shared libs), for
GNU/Linux 2.6.32,
BuildID[sha1]=0xb372fe4bb8536c54a3ac70df31537516ec7b8d2d, not stripped

build incantation for lp_test_printf looks like so:
g++  -L/usr/lib64/llvm  -lpthread -lffi -ldl -lm  lp_test_printf.o
lp_test_main.o -o lp_test_printf -Wl,--start-group  -L../../auxiliary/
-lgallium libllvmpipe.a -lLLVMBitWriter -lLLVMPowerPCCodeGen
-lLLVMSelectionDAG -lLLVMPowerPCDesc -lLLVMAsmPrinter -lLLVMMCParser
-lLLVMPowerPCAsmPrinter -lLLVMPowerPCInfo -lLLVMJIT
-lLLVMExecutionEngine -lLLVMCodeGen -lLLVMScalarOpts -lLLVMInstCombine
-lLLVMTransformUtils -lLLVMipa -lLLVMAnalysis -lLLVMTarget -lLLVMMC
-lLLVMCore -lLLVMSupport  -lXext -lXdamage -lXfixes -lX11-xcb -lX11
-lxcb-glx -lxcb -lXxf86vm   -ldrm   -lm -lpthread -ldl -Wl,--end-group

A bit of time inside gdb:

Reading symbols
from /home/willschm/llvm/mesa/src/gallium/drivers/llvmpipe/lp_test_printf...done.
(gdb) r
Starting
program: /home/willschm/llvm/mesa/src/gallium/drivers/llvmpipe/lp_test_printf 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".

Program received signal SIGSEGV, Segmentation fault.
0x7c0802a6f8010010 in ?? ()
(gdb) bt
#0  0x7c0802a6f8010010 in ?? ()
#1  0x000000001001df40 in test_printf (gallivm=0x10a11e80, 
    testcase=<error reading variable: Unhandled dwarf expression opcode 0xfa>, 
    fp=<error reading variable: Unhandled dwarf expression opcode 0xfa>, 
    verbose=<error reading variable: Unhandled dwarf expression opcode 0xfa>) at lp_test_printf.c:112
#2  0x000000001001e040 in test_all (fp=<optimized out>, verbose=<optimized out>, gallivm=<optimized out>)
    at lp_test_printf.c:125
#3  test_some (gallivm=<optimized out>, verbose=<optimized out>, fp=<optimized out>, n=<optimized out>)
    at lp_test_printf.c:135
#4  0x00000000100150e0 in main (argc=1, argv=<optimized out>) at lp_test_main.c:401


Some single-step debug near the point of SIGSEGV suggests that we are
reading a bad pointer value off of $r3 and hit the segv on the btctr.  

Breakpoint 1, test_printf (gallivm=0x10a11e80, 
    testcase=<error reading variable: Unhandled dwarf expression opcode 0xfa>, 
    fp=<error reading variable: Unhandled dwarf expression opcode 0xfa>, 
    verbose=<error reading variable: Unhandled dwarf expression opcode 0xfa>) at lp_test_printf.c:112
112	   test_printf_func(0);
   0x000000001001df20 <test_printf+432>:	e9 43 00 00	ld      r10,0(r3)
=> 0x000000001001df24 <test_printf+436>:	f8 41 00 28	std     r2,40(r1)

(gdb) info reg r3
r3             0xfffb7f60010	17590977429520
(gdb) info reg r10
r10            0x7c0802a6f8010010	8937396376665391120


   0x000000001001df28 <test_printf+440>:	7c 69 1b 78	mr      r9,r3
   0x000000001001df2c <test_printf+444>:	38 60 00 00	li      r3,0
   0x000000001001df30 <test_printf+448>:	7d 49 03 a6	mtctr   r10
   0x000000001001df34 <test_printf+452>:	e9 69 00 10	ld      r11,16(r9)
   0x000000001001df38 <test_printf+456>:	e8 49 00 08	ld      r2,8(r9)
=> 0x000000001001df3c <test_printf+460>:	4e 80 04 21	bctrl


C code for that chunk should match this; so seems like something went wrong
handling the return from LLVMGetPointerToGlobal.  (32/64-bit ism?) 

>   code = LLVMGetPointerToGlobal(engine, test);
>   test_printf_func = (test_printf_t) pointer_to_func(code);
> 
>    // LLVMDumpModule(module);
> 
>    test_printf_func(0);


Thanks, 
-Will