psABI: ARM, x86, … C++ Itanium ABI Microsoft Windows ABIs C++ Standard 18armv8-a System V ABI - iPhone - M1 Mac and newer - Android smartphone x86-64 (AMD64) System V ABI - Linux server - old Mac (AMD64) Microsoft ABI - Windows device armv7-a System V ABI - ancient iPhone - low-end Android smartphone x86 (IA-32) System V ABI - ancient Linux server x86 (IA-32) Microsoft ABI - ancient Windows Windows device 19armv8-a System V ABI Procedure Call Standard for the Arm® 64-bit Architecture armv8-a clang 18.1.0 -O2 -std=c++20 x86-64 (AMD64) System V ABI AMD64 Architecture Processor Supplement

mo/src/main.cpp:70 frame #1 : 0x0000555555583b08 in std::__1::coroutine_handle::resume[abi:ne180100]() const () at /usr/lib/llvm-18/include/c++/v1/__coroutine/coroutine_handle.h:69 frame namespace)::word_stats, fal frame #1 : 0x0000555555583b08 in std::__1::coroutine_handle::resume[abi:ne180100]() co frame #2 : 0x0000555555584045 in unifex::_ch::continuation_handle::resume() namespace)::word_stats, false>::type ( 1 : 0x0000555555583b08 in std::__1::coroutine_handle::resume[abi:ne180100]() const () at / 2 : 0x0000555555584045 in unifex::_ch::continuation_handle::resume()

= basic_simd_mask; template Abi = ...> class basic_simd; template Abi> class basic_simd_mask; • simd behaves just like T (element-wise) vs. element-sized masks (array of bool is not unheard of), • SIMD width simd::size • Abi determines width and ABI (i.e. how parameters are passed to functions) • Example: simd on x86 can be two = basic_simd_mask; template Abi = ...> class basic_simd; template Abi> class basic_simd_mask; • simd behaves just like T (element-wise)

Reflection in C++ as per P2996 Syntax and examples Reflection libraries! Python bindings ABI hashing (boost::abi_hash?) A duck-typed std::any (boost::virtual_any?) Alternatives ways to achieve “reflection” Reflection libaries! 42Now let's do some actual library design Automatic python bindings Automatic type ABI hash A better std::any with duck typing 43Python bindings 44We have a C++ class that we’d like to Customizations are trickier / not DRY We have two potential approaches Python bindings - Summary 54ABI hashing 55Say you had a unique hash for a type’s memory layout. What would you do? We’d like

except.elf except.cpp -std=c++20 -Os -g -fexceptions -frtti -mcpu=cortex-m4 -mfloat-abi=hard -mthumb --specs=nosys.specs --specs=nano.specs --Wl,-T linker.ld Let's start simple [[gnu::noinline]] hereItanium C++ ABI: What are throws? 107Itanium C++ ABI: Throw guidelines void __cxa_throw( void* thrown_exception, std::type_info* type_info, void (*dtor)(void*)); 108Itanium C++ ABI: How __cxa_allocate_exception register_t r11; register_t ip; register_t sp; register_t lr; register_t pc; }; Itanium C++ ABI: What is the Exception Header? struct exception_header { cortex_m_cpu cpu{}; std::type_info*

Visual StudioProblem 1: ABI incompatible C++ binaries Compiler Compiler version Target OS Target architecture Optional library features Other compiler flagsProblem 1: ABI incompatible C++ binaries everything together Download source package Build package Integrate into projectProblem 1: ABI incompatible C++ binaries Solution 1: Build C++ dependencies from source Benefits of building from developers and CI builds •For every build, calculate an ABI hash to uniquely identify it.An ABI hash calculation with binary caching in vcpkg ABI Hash Source files Target configuration Compilers

lib2: g1, g2, g3 14Interposition • Overriding a symbol in one binary from another. • Fundamental ABI design pillar! • Alleged motivation: • Mimic the behavior of static libs: first definition shadows 0x1234 void f() {...} jmp [.got+4] 0x1234 C++ Implication #4: Comparing Func Ptrs From the SystemV ABI doc: To allow comparisons of function addresses to work as expected, if an executable file references such a definition in the executable 33 https://gitlab.com/x86-psABIs/x86-64-ABI/-/jobs/artifacts/master/raw/x86-64-ABI/abi.pdf?job=build auto* pf = &f; lib1 .dynsym f: .plt_exe+8C++ Implication

__last); template ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 2 3 void __sort_impl(_RandomAccessIterator __first, _RandomAcces 4 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 2 3 void __sort_impl(_RandomAccessIterator __first, _RandomAcces 4 // ... 5 Shuffle the range before 29.1PROBLEM: TIES. HOW _LIBCPP_HIDE_FROM_ABI static static char __x; return reinterpret_cast(&__x); } 30PROBLEM: TIES. HOW _LIBCPP_HIDE_FROM_ABI static uint_fast64_t __seed() { static char __x; return reinterpret_cast(&__x); } Address

extensions ON -- The C compiler identification is GNU 9.4.0 -- Detecting C compiler ABI info -- Detecting C compiler ABI info - done -- Check for working C compiler: /usr/bin/arm-linux-gnueabihf-gcc-9 - /main hello/0.1: Hello World Release! hello/0.1: __x86_64__ defined hello/0.1: _GLIBCXX_USE_CXX11_ABI 1 hello/0.1: __cplusplus201703 hello/0.1: __GNUC__11 hello/0.1: __GNUC_MINOR__1 hello/0.1 test_package cpp folder, that file will be responsible of including the right toolchain depending on the ANDROID_ABI variable that indicates the build configuration that the IDE is currently running: Listing 41: co

The Structure of a Program 58Copyright © 2020 Bob Steagall K E W B C O M P U T I N G What is an ABI? • ABI (application binary interface) is the platform-specific specification of how entities defined Calling conventions for making system calls • On Linux, GCC and Clang use the Itanium ABI; On Windows, MSVC uses its own ABI CppCon 2020 - The Structure of a Program 59Copyright © 2020 Bob Steagall K E W reflect these addresses • It emits executable code • The compiler and the linker must agree on the ABI • Both must understand object code in exactly the same way CppCon 2020 - The Structure of a Program