boost context does not preserve fpu context on ios arm64 devices

[ykirpichev@…]

The problem with floating point calculations was observed when trying to use boost context on arm64 ios devices. It looks like, in certain conditions floating point arithmetic stops working properly.

It is hard to provide exact way how to reproduce the issue, but after investigation it has been found out that VFP_FP is not defined by clang++ when the following command is executed:

"/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang++" -x assembler-with-cpp -O3 -finline-functions -Wno-inline -Wall -gdwarf-2 -fexceptions -DBUNDLE_VERSION=1.60.0.yandex.4 -DYANDEX_BOOST -DMOBILE_BUILD -O2 -Wno-unused-variable -Wno-unknown-pragmas -Wno-reorder -Wno-unused-local-typedefs -stdlib=libc++ -fobjc-arc -fvisibility=hidden -Qunused-arguments -lc++ -miphoneos-version-min=6.1 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS9.3.sdk -isystem /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS9.3.sdk/usr/include -arch arm64 -fembed-bitcode -O2 -arch arm64 -DBOOST_ALL_NO_LIB=1 -DBOOST_ATOMIC_STATIC_LINK=1 -DBOOST_CHRONO_STATIC_LINK=1 -DBOOST_CONTEXT_SOURCE -DBOOST_DISABLE_ASSERTS -DBOOST_SYSTEM_NO_DEPRECATED -DBOOST_SYSTEM_STATIC_LINK=1 -DBOOST_THREAD_BUILD_LIB=1 -DBOOST_THREAD_POSIX -DBOOST_THREAD_USE_LIB=1 -DNDEBUG -I"." -c -o "bin.v2/libs/context/build/6a8dcaa993b5623b8882ae19f514636b/asm/jump_arm64_aapcs_macho_gas.o" "libs/context/src/asm/jump_arm64_aapcs_macho_gas.S"

As a result floating point context is not stored/restored and eventually leads to some mysterious issues.

The problem can be solved by defining VFP_FP directly, however, better way to fix it is to remove #if (defined(VFP_FP) && !defined(SOFTFP)) from jump_arm64_aapcs_macho_gas.S.

[olli]

hmm - preserving FPU is removed in version 1.61. Could you check branch develop?

[ykirpichev@…]

Replying to olli:

hmm - preserving FPU is removed in version 1.61. Could you check branch develop?

Yes, I saw it, that is why I'm wondering why it is removed in version 1.61? It will break usage of floating point in coroutines on arm64 ios devices.

[ykirpichev@…]

Replying to olli:

hmm - preserving FPU is removed in version 1.61. Could you check branch develop?

Yes, I saw it, that is why I'm wondering why it is removed in version 1.61? It will break usage of floating point in coroutines on arm64 ios devices.

[ykirpichev@…]

Replying to olli:

hmm - preserving FPU is removed in version 1.61. Could you check branch develop?

Yes, I saw it, that is why I'm wondering why it is removed in version 1.61? It will break usage of floating point in coroutines on arm64 ios devices.

[Yury Kirpichev <ykirpichev@…>]

Sorry, I added previous comment several time by accident. Do you want me to try newer boost version and check whether problem exist? I can relatively easily check version 1.61 beta. Is it ok?

[olli]

Replying to Yury Kirpichev <ykirpichev@…>:

Sorry, I added previous comment several time by accident. Do you want me to try newer boost version and check whether problem exist? I can relatively easily check version 1.61 beta. Is it ok?

would be nice, if you could test 1.61 on this platform

[olli]

fixed in commit f3d3ca3ab8b747c3efde7d1b26602be1f01eafbf (branch develop). could you verify that the fix works on IOS, please? ARM64 + ELF (Linux) seams to work.