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GRodr21's avatar
GRodr21
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6 years ago

C standard headers and macros

Hello: I am having some trouble with C standard headers and macros in my kernels. I am trying to use some intrincate macros that work fine when they are resolved by the gcc preprocessor. However, ao...
HRZ's avatar
HRZ
Icon for Frequent Contributor rankFrequent Contributor
6 years ago

"aoc" is an OpenCL compiler, not a C compiler, and OpenCL only supports a subset of C at kernel level. Macros are certainly supported by aoc, but I am not sure what you are trying to do that requires including of C standard headers. Maybe if you post a simplified example kernel that shows the issue, we would be able to find a solution/work-around. At the same time, you can try compiling your kernel against NVIDIA or AMD's OpenCL SDK; if it still didn't work, then you know what you are trying to do is not supported in OpenCL.

GRodr25's avatar
GRodr25
Icon for New Contributor rankNew Contributor
6 years ago

Since the problem stems from the files that contain the macros including standard C headers I am trying to reproduce the scenario with this minimal kernel:

#include <string.h>

__kernel void prueba() {

int a = 1;

}

Since aoc cannot find string.h I compile this kernel with:

aoc -I /usr/include -march=emulator min_example.cl

Then aoc outputs it cannot find stdef.h, so I include a new directory:

aoc -I /usr/include -I /usr/include/linux -march=emulator min_example.cl

Then 21 errors are generated. Among them:

In file included from /usr/include/string.h:633:

/usr/include/bits/string2.h:972:3: error: OpenCL does not support the 'register' storage class specifier

register size_t __result = 0;

/usr/include/bits/string2.h:1128:25: error: use of undeclared identifier 'NULL'

return *__s == '\0' ? NULL : (char *) (size_t) __s;

Any idea of what is going on here?

Edit:

It seems OpenCL 1.0 will not allow including string.h, among other C99 headers (https://www.khronos.org/registry/OpenCL/sdk/1.0/docs/man/xhtml/restrictions.html). Does this apply to the OpenCL version leveraged by Intel FPGA SDK for OpenCL?

Edit2:

According to https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/hb/opencl-sdk/aocl_programming_guide.pdf (A.1.2 p.193) Intel FPGA SDK for OpenCL has this restriction.