[PATCH v4] libstdc++: Implement C++26 <debugging> features (P2546R5)

[Sam James]

Jonathan Wakely <jwakely@redhat.com> writes:

> [...]
> +void
> +std::breakpoint() noexcept
> +{
> +  PROBE(std::breakpoint);
> +
> +  if (__gnu_cxx::debugger_signal_for_breakpoint > 0)
> +    std::raise(__gnu_cxx::debugger_signal_for_breakpoint);
> +

glib's https://gitlab.gnome.org/GNOME/glib/-/blob/main/glib/gbacktrace.h#L58 is
a useful reference. It has an entry for alpha and also MSVC (though I
can't imagine MSVC matters here).

> +#if _GLIBCXX_HAVE_DEBUGAPI_H && defined(_WIN32) && !defined(__CYGWIN__)
> +  DebugBreak();
> +#elif __has_builtin(__builtin_debugtrap)
> +  __builtin_debugtrap(); // Clang
> +#elif defined(__i386__) || defined(__x86_64__)
> +  __asm__ volatile ("int3; nop");
> +#elifdef __thumb__
> +  __asm__ volatile (".inst 0xde01");
> +#elifdef __aarch64__
> +  __asm__ volatile (".inst 0xd4200000");
> +#elifdef __arm__
> +  __asm__ volatile (".inst 0xe7f001f0");
> +#elifdef __riscv
> +  /* section 2.8 in the RISC-V unprivileged ISA manual says for semi-hosted
> +   * environments we want the sequence:
> +   * slli x0, x0, 0x1f     # Entry NOP
> +   * ebreak         # Break to debugger
> +   * srai x0, x0, 7    # NOP encoding the semihosting call number 7
> +   */
> +  __asm__ volatile (".4byte 0x00100073");
> +#elifdef __powerpc__
> +  __asm__ volatile(".4byte 0x7d821008");
> +#else
> +  __builtin_trap();
> +#endif
> +} // If the debugger stops here, std::breakpoint() was called.
> +
> [...]