Understanding hardfp Abi

Abi is "application binary interface", that is, the compilerCodeA rule used for compiling code.

Abi specifications generally include:

(1) Expression of C type (INT, short, long, union, struct ...)

(2) calling convention, including: how to pass function parameters and return values; if registers and stacks are used.

 

When compiling a function with floating-point parameters, there are three possible compilation options:-mfloat-Abi = soft/softfp/hard.

"Soft" option: indicates that the FPU hardware is not used, but the GCC integer arithmetic operation is used to simulate floating point operations.

"Softfp" option: indicates that you want to use FPU hardware for floating point operations, but the arguments of the function are passed to the integer register (r0-r3) and then passed to the FPU.

"Hard" option: indicates that you want to use FPU hardware for floating point operations, and the function parameters are directly transferred to the FPU register (S0, D0.

 

The hardfp abi and hardfloat operations are not the same thing.

Hardfp Abi is also known as the ABI in VFP mode. It is only a compilation rule, while hardfloat indicates that FPU is used for floating point operations.

Soft abi and softfp Abi are collectively referred to as the standard mode Abi.

 

Therefore, when a floating point function is called,

Apps or libraries compiled with-mfloat-Abi = soft can be run in OS compiled with-mfloat-Abi = softfp;

Apps or libraries compiled with-mfloat-Abi = softfp cannot be run in OS compiled with-mfloat-Abi = soft.

-Mfloat-Abi = softfp/soft and-mfloat-Abi = hard are incompatible.

 

Note: Code sourcery 2007/2008 does not support-mfloat-Abi = hard. It is supported from code sourcery 2009q1-mfloat-Abi = hard.

 

Meego starts from 1.2.0 and all basic libraries are compiled with-mfloat-Abi = hard. The RPM package architecture is called "armv7hl", while the scheduler in OBS is called "armv8el ".

Using "armv8el" instead of "armv7hl" as the OBS scheduler is a historical reason. meego officially planned to change the "armv8el" scheduler to "armv7hl" in the future ", but with the closure of the meego project, it may not be changed.