Access to ARM hardware
Hi Matt, This week I found an error in LLVM that can only be reproduced on ARM hardware, if the GCC that compiles it specifies --mcpu=cortex-a15. The error is a segfault on one of the tests compiled by that Clang/LLVM. As you can see, it's not something trivial that we'd expect people to do easily. My question is: How do we tackle this type of bug? One option is to do all the debugging and interface with the original patch author until we fix the problem. This works well for simple bugs, but in this case I'm not sure it will work. Another option was to have a board on Linaro's DMZ with no access to anything else internally, so that people could log in and debug the problem in situ. This board would have to be setup just for the debugging with a random password given only to the author of the patch and cleaned up right after the bug is fixed (to avoid external abuse). We could use the same board for LLVM, GCC, GDB, etc. but it should be easy to re-flash it to a minimum system, so that we don't spend too much time setting it up. Does anyone have a better idea? cheers, --renato ___ linaro-toolchain mailing list linaro-toolchain@lists.linaro.org http://lists.linaro.org/mailman/listinfo/linaro-toolchain
clang + VFP
Hi.
First.
#include
I'm trying to use a current clang/llvm (current as in git checkout
from just the other day) to build an opencl kernel and then link that
with some code which has been compiled with gcc/g++.
When the clang .o is linked to the gcc/gcc+, I'm getting
/home/tgall/opencl/SNU/tmp2/cl_temp_1.tkl uses VFP register arguments,
/home/tgall/opencl/SNU/tmp2/cl_temp_1.o does not
the cl_temp_1.o was produced with clang.
the cl_temp_1.tkl via gcc/g++.
Let's dive into details.
This is following in the footsteps of an open source framework called
SNU which implements OpenCL. Within SNU they had a fairly old version
of clang+llvm which wouldn't even build on ARM so step one has been to
figure out what SNU was doing with clang and replicate this using
latest clang.
So given the following minimal test kernel placed into cl_temp_1.cl
/* Header to make Clang compatible with OpenCL */
#define __global __attribute__((address_space(1)))
int get_global_id(int index);
/* Test kernel */
__kernel void test(__global float *in, __global float *out) {
int index = get_global_id(0);
out[index] = 3.14159f * in[index] + in[index];
}
then we following the following steps:
clang -mfloat-abi=hard -mfpu=neon -S -emit-llvm -x cl
-I/home/tgall/opencl/SNU/src/compiler/tools/clang/lib/Headers
-I/home/tgall/opencl/SNU/inc -include
/home/tgall/opencl/SNU/inc/comp/cl_kernel.h
/home/tgall/opencl/SNU/tmp2/cl_temp_1.cl -o
/home/tgall/opencl/SNU/tmp2/cl_temp_1.ll
with the resulting cl_temp_1.ll we:
llc /home/tgall/opencl/SNU/tmp2/cl_temp_1.ll
which results in cl_temp_1.s. Then:
clang -c -mfloat-abi=hard -mfpu=neon -o
/home/tgall/opencl/SNU/tmp2/cl_temp_1.o
/home/tgall/opencl/SNU/tmp2/cl_temp_1.s
so now in theory we should have a perflectly good cl_temp_1.o ready for linking.
But first let's get the bits ready that will be built by the
traditional gnu toolschain. We have:
gcc -shared -fPIC -O3 -o /home/tgall/opencl/SNU/tmp2/cl_temp_1_info.so
/home/tgall/opencl/SNU/tmp2/cl_temp_1_info.c
and
gcc -shared -fPIC -march=armv7-a -mtune=cortex-a9 -mfloat-abi=hard
-mfpu=neon -fsigned-char -DDEF_INCLUDE_ARM -I. -I
/home/tgall/opencl/SNU/src/runtime/hal/device/cpu -I
/home/tgall/opencl/SNU/src/runtime/include -I
/home/tgall/opencl/SNU/src/runtime/core -I
/home/tgall/opencl/SNU/src/runtime/core/device -I
/home/tgall/opencl/SNU/src/runtime/hal -I
/home/tgall/opencl/SNU/src/runtime/hal/device -DTARGET_MACH_CPU -O3 -c
/home/tgall/opencl/SNU/src/runtime/hal/device/cpu/hal.c -o
/home/tgall/opencl/SNU/tmp2/hal.o
And here we try to link it all together.
g++ -shared -fPIC -march=armv7-a -mtune=cortex-a9 -mfloat-abi=hard
-mfpu=neon -fsigned-char -DDEF_INCLUDE_ARM -O3 -o
/home/tgall/opencl/SNU/tmp2/cl_temp_1.tkl
/home/tgall/opencl/SNU/tmp2/hal.o
/home/tgall/opencl/SNU/tmp2/cl_temp_1.o
-L/home/tgall/opencl/SNU/lib/lnx_arm
-lsnusamsung_opencl_builtin_lnx_arm -lpthread -lm
and bang we're back to the error I first mentioned:
/usr/bin/ld: error: /home/tgall/opencl/SNU/tmp2/cl_temp_1.tkl uses VFP
register arguments, /home/tgall/opencl/SNU/tmp2/cl_temp_1.o does not
so first obvious question is -mfloat-abi=hard -mfpu=neon correct for clang?
tgall@miranda:~/opencl/SNU/tmp2$ clang --version
clang version 3.3
Target: armv7l-unknown-linux-gnueabihf
Thread model: posix
Thanks for any suggestions!
--
Regards,
Tom
"Where's the kaboom!? There was supposed to be an earth-shattering
kaboom!" Marvin Martian
Tech Lead, Graphics Working Group | Linaro.org │ Open source software
for ARM SoCs
w) tom.gall att linaro.org
h) tom_gall att mac.com
___
linaro-toolchain mailing list
linaro-toolchain@lists.linaro.org
http://lists.linaro.org/mailman/listinfo/linaro-toolchain
