Improve Armv7-R documentation - #162654
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People have fallen over the issue where `target-cpu=cortex-r5` unexpectedly turns on FPU support, even on an EABI soft-float target. So this update attempts to document the full set of Armv7-R processors, their FPU options, and how to set things up for the precise combination you have. It is modelled after the Armv7E-M documentation.
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Some changes occurred in src/doc/rustc/src/platform-support cc @Noratrieb |
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People have fallen over the issue where
target-cpu=cortex-r5unexpectedly turns on FPU support, even on an EABI soft-float target. So this update attempts to document the full set of Armv7-R processors, their FPU options, and how to set things up for the precise combination you have.It is modelled after the Armv7E-M documentation.
I know the features it recommends are "unstable" but I really do not know any other way of controlling what kind of FPU
rustcis generating code for. I'd love a simple-Ctarget-cpu=cortex-r5 -Ctarget-fpu=vfp3-d16-spoption but we don't have one at this time.This actually matters more on Armv7-R than on Armv7E-M, because
rustccurrently assumes a double-precision FPU and some hardware only has a single-precision FPU. So you need target features to make the target work on that hardware.