Difference between revisions of "ARM compiler options"
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* The softfp/vfpv2 distinction for armel indicates how the fp operations are performed. | * The softfp/vfpv2 distinction for armel indicates how the fp operations are performed. | ||
** Softfp means that all fp operations are performed by software | ** Softfp means that all fp operations are performed by software | ||
| − | ** vfpv2 means that fp operations are performed by the hardware. Although fp values are still passed in integer registers, they're copied to fp registers before performing the operation. | + | ** vfpv2, vfpv3 means that fp operations are performed by the hardware. Although fp values are still passed in integer registers, they're copied to fp registers before performing the operation. |
From an ABI point of view softfp and vfpv2 are compatible. However, vfpv2 executables will crash if run on a processor not having vfpv2 hardware. | From an ABI point of view softfp and vfpv2 are compatible. However, vfpv2 executables will crash if run on a processor not having vfpv2 hardware. | ||
Revision as of 12:13, 12 January 2014
Overview
The FPC compiler lets you create (cross)compilers for various ARM instruction sets, floating point units etc.
Current (FCP 2.6.x/2.7.x) compilers (and RTL PPUs etc) are built for just one ABI and cannot output other ABIs once built - e.g. dding -dFPC_ARMHF when compiling a program will not change anything: http://lists.freepascal.org/lists/fpc-devel/2013-May/032093.html
The options below are passed in OPTS= when building FPC. When building a cross copmiler, some of them can be passed in CROSSOPT as well.
ABI
ABIs are selected using the -Ca switch.
Note: Normally, specifying an ABI is not needed. Source: http://www.mail-archive.com/fpc-pascal@lists.freepascal.org/msg35496.html- default: ?
- eabi: ?
- EABI HF is selected using
-dFPC_ARMHF; the -Ca eabihf option is present but is not necessary (but may not hurt). (Source: http://www.mail-archive.com/fpc-pascal@lists.freepascal.org/msg35487.html)
Instruction sets
Instructions sets are selected using the -Cp switch. Possible instruction sets (note many sets are backward compatible):
- ARMV3
- ARMV4
- ARMV4T
- ARMV5: e.g. in Nokia N900
- ARMV5T
- ARMV5TEJ
- ARMV6: e.g. in Raspberry Pi; will probably work on most current hardware
- ARMV6K
- ARMV6T2
- ARMV6Z
- ARMV7
- ARMV7A
- ARMV7R
- ARMV7M
- ARMV7EM
Floating point support
Floating point support coprosessor (FPU) options are selected with the -Cf switch Possible FPU support options:
- soft: softfloat/no FPU support.
- vfpv2: e.g. on Raspberry Pi
- vfpv3
- vfpv3_d16
Interactions
Below adapted from: [1]
- armel and armhf indicate how floating point (fp) values are passed.
- Armel means that all floating point values are always passed in integer registers.
- Armhf means that fp values are generally passed in floating point registers. As indicated above, armhf is settable by
-dFPC_ARMHF; see above)
- The softfp/vfpv2 distinction for armel indicates how the fp operations are performed.
- Softfp means that all fp operations are performed by software
- vfpv2, vfpv3 means that fp operations are performed by the hardware. Although fp values are still passed in integer registers, they're copied to fp registers before performing the operation.
From an ABI point of view softfp and vfpv2 are compatible. However, vfpv2 executables will crash if run on a processor not having vfpv2 hardware.
Other relevant options
- If you are using FPC 2.7.1+, and want to speed up floating point, you can also speicfy -OoFASTMATH to sacrifice precision for performance.
- -fPIC: does this need to be mentioned?
