How can I tell the linker/compiler not to use memset/memcpy function which use FPU registers?
For example: SCIOPTA allows to limit the use of the FPU for certain tasks (to improve task-switching). Tasks without FPU may not use FPU registers. But the compiler/linker uses optimized versions of memset() which results in an exception.
I tried to compile C files with --fpu none, but this produces link-timer errors.
Hi,
I'm afraid there's no easy way to avoid this with the ARM Compilation tools. At link time, if any of the user code was built for VFP then by default armlink will choose a library that is allowed to use the VFP. It is possible to override the linker's default choice, and force it to use a non-VFP library (see later), but that choice applies to the entire image, so that both your non-VFP and VFP-using functions will end up calling an inefficient non-VFP library.
When compiling with "--cpu=Cortex-A8", the compiler assumes VFP and NEON are allowed. To have better control over this, one solution is to compile your non-VFP using functions with "--fpu=SoftVFP", and the VFP-using functions with "--fpu=SoftVFP+VFPv3". These are link-time compatible. The linker will select the library functions that use floating point instructions but pass floating point parameters in core registers. As floating point instructions are still used by the library, that might not be sufficient to achieve the your goal of running some tasks entirely in soft-floating point and some in hard-floating point.
If all your code is compiled with either "--fpu=SoftVFP" or "--fpu=SoftVFP+VFPv3", the linker’s default choice of an "--fpu=SoftVFP+VFPv3" library can be overridden by adding the name of the soft floating point only library on the linker command line. In this case no library functions will use hardware floating point, so this is context switch safe, although will not be high performance if your VFP-using code makes heavy use of library functions. To find the software floating point library location, compile all files with "--fpu=SoftVFP" and use the linker option "--info=libraries" to list the libraries that the linker actually selected.
The only other solution would be to build _two_ executables, one containing the VFP-using functions and VFP libraries, and the other containing the non-VFP-using functions and non-VFP libraries, then join the two executables together somehow.
The C libraries provided in ARM Compiler 5.04 contains several variants of the memmove/memset routines, and the linker selects which variantto use according to the build attributes in the files being linked. If a file included in the link has an attribute indicating that it uses FPU instructions then the linker takes that to mean it is OK to use the variants of memmove/memset which use FPU instructions.
Obviosuly this does not work in your special case if your application could be using FPU instruction but only under special cirumstances.
One way around this is to create your own copy of the C library and remove the variants of memmove/memset that use FPU instructionfrom the library. Then the linker will have to use the non FPU variants of memmove/memset.
Copy the version of the ARM C library that you are linking with (here I am assuming it is c_2.l, the library name convention used is documented athttp://infocenter.arm.com/help/topic/com.arm.doc.dui0475j/chr1358938936497.html.Use the --info=libraries option to the linker to list the libraries your application is actually linking with):
cp $ARMLIB/armlib/c_2.l c_2.l
List all files in the library that containt the NEON variants of memmove/memset/etc (this step is just informative):
armar -t c_2.l | grep rt_neon_mem
Remove these files from your copy of your library
armar -d c_2.l `armar -t c_2.l | grep rt_neon_mem` Now use this modified c_2.l library to link with your application; the application should not longer be using versions of memmove/memset which contain FPU instructions.
Ok, thanks. I will give it a try.