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MIPS/libunwind: Use -mfp64 if compiler is FPXX (#68521)

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Libunwind supports FP64 and FP32 modes, but not FPXX. The reason is
that, FP64 and FP32 have different way to save/restore FPRs. If
libunwind is built as FPXX, we have no idea which one should we use.

It's not due to the code bug, but rather the nature of FPXX.
FPXX is an ABI which uses only a common subset of FR=1(FP64) and FR=0
(FP32).
So that FPXX binaries can link with both FP64 and FP32 ones, aka.
    FPXX + FP32 -> FP32
    FPXX + FP64 -> FP64

While for libunwind, we should save/restore all of FPRs. If we use FPXX,
we can only save/restore a common subset of FPRs, instead of superset.

If libunwind is built as FP64, it will interoperatable with FPXX/FP64
APPs, and if it is built as FP32, it will interoperatable with
FP32/FPXX. Currently most of O32 APPs are FPXX or FP64, while few are
FP32.

So if the compiler is FPXX, which is the default value of most
toolchain, let's switch it to FP64.

Co-authored-by: YunQiang Su <yunqiang.su@cipunited.com>
(cherry picked from commit 4520b478d2512b0f39764e0464dcb4cb961845b5)
This commit is contained in:
YunQiang Su 2024-02-08 09:15:53 +08:00 committed by Tom Stellard
parent a8158d8836
commit 2b033a32ea
1 changed files with 19 additions and 0 deletions
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19
libunwind/CMakeLists.txt
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@ -21,6 +21,7 @@ set(LIBUNWIND_LIBCXX_PATH "${CMAKE_CURRENT_LIST_DIR}/../libcxx" CACHE PATH
"Specify path to libc++ source.")
include(GNUInstallDirs)
include(CheckSymbolExists)
#===============================================================================
# Setup CMake Options
@ -96,6 +97,20 @@ endif()
option(LIBUNWIND_HIDE_SYMBOLS
"Do not export any symbols from the static library." ${LIBUNWIND_DEFAULT_HIDE_SYMBOLS})
# If toolchain is FPXX, we switch to FP64 to save the full FPRs. See:
# https://web.archive.org/web/20180828210612/https://dmz-portal.mips.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking
check_symbol_exists(__mips_hard_float "" __MIPSHF)
check_symbol_exists(_ABIO32 "" __MIPS_O32)
if (__MIPSHF AND __MIPS_O32)
file(WRITE ${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/mips_is_fpxx.c
"#if __mips_fpr != 0\n"
"# error\n"
"#endif\n")
try_compile(MIPS_FPABI_FPXX ${CMAKE_BINARY_DIR}
${CMAKE_BINARY_DIR}${CMAKE_FILES_DIRECTORY}/CMakeTmp/mips_is_fpxx.c
CMAKE_FLAGS -DCMAKE_C_LINK_EXECUTABLE='echo')
endif()
#===============================================================================
# Configure System
#===============================================================================
@ -179,6 +194,10 @@ if (WIN32)
add_compile_flags_if_supported(-Wno-dll-attribute-on-redeclaration)
endif()
if (MIPS_FPABI_FPXX)
add_compile_flags(-mfp64)
endif()
# Get feature flags.
# Exceptions
# Catches C++ exceptions only and tells the compiler to assume that extern C