[PATCH] libstdc++: Implement C++26 <debugging> features (P2546R5)
Peter0x44
peter0x44@disroot.org
Mon Jun 3 13:34:56 GMT 2024
On 2024-06-01 03:22, Jonathan Wakely wrote:
> Here's an implementation of the C++26 <debugging> header.
>
> We should really have some tests that invoke GDB and check that the
> breakpoint works when a debugger is attached. That seems tricky to do
> via the main conformance.exp testsuite. It could be done via the
> prettyprinters.exp testsuite, which already uses GDB, but would require
> some changes to the gdb-test procedure, which assumes it needs to
> insert
> its own breakpoint at marked spots in the code.
>
> I think we could add this without those tests, and improve it later.
>
> -- >8 --
>
> It would be good to provide a macOS definition of is_debugger_present,
> but that isn't included in this change.
>
> libstdc++-v3/ChangeLog:
>
> * config.h.in: Regenerate.
> * configure: Regenerate.
> * configure.ac: Check for facilities needed by <debugging>.
> * include/Makefile.am: Add new header.
> * include/Makefile.in: Regenerate.
> * include/bits/version.def (debugging): Add.
> * include/bits/version.h: Regenerate.
> * src/c++26/Makefile.am: Add new file.
> * src/c++26/Makefile.in: Regenerate.
> * include/std/debugging: New file.
> * src/c++26/debugging.cc: New file.
> * testsuite/19_diagnostics/debugging/breakpoint.cc: New test.
> * testsuite/19_diagnostics/debugging/breakpoint_if_debugging.cc:
> New test.
> ---
> libstdc++-v3/config.h.in | 9 ++
> libstdc++-v3/configure | 22 +++
> libstdc++-v3/configure.ac | 9 ++
> libstdc++-v3/include/Makefile.am | 1 +
> libstdc++-v3/include/Makefile.in | 1 +
> libstdc++-v3/include/bits/version.def | 9 ++
> libstdc++-v3/include/bits/version.h | 10 ++
> libstdc++-v3/include/std/debugging | 82 ++++++++++++
> libstdc++-v3/src/c++26/Makefile.am | 4 +-
> libstdc++-v3/src/c++26/Makefile.in | 7 +-
> libstdc++-v3/src/c++26/debugging.cc | 126 ++++++++++++++++++
> .../19_diagnostics/debugging/breakpoint.cc | 9 ++
> .../debugging/breakpoint_if_debugging.cc | 9 ++
> 13 files changed, 295 insertions(+), 3 deletions(-)
> create mode 100644 libstdc++-v3/include/std/debugging
> create mode 100644 libstdc++-v3/src/c++26/debugging.cc
> create mode 100644
> libstdc++-v3/testsuite/19_diagnostics/debugging/breakpoint.cc
> create mode 100644
> libstdc++-v3/testsuite/19_diagnostics/debugging/breakpoint_if_debugging.cc
>
> diff --git a/libstdc++-v3/config.h.in b/libstdc++-v3/config.h.in
> index 486ba450749..07203815459 100644
> --- a/libstdc++-v3/config.h.in
> +++ b/libstdc++-v3/config.h.in
> @@ -70,6 +70,9 @@
> /* Define to 1 if you have the `cosl' function. */
> #undef HAVE_COSL
>
> +/* Define to 1 if you have the <debugapi.h> header file. */
> +#undef HAVE_DEBUGAPI_H
> +
> /* Define to 1 if you have the declaration of `strnlen', and to 0 if
> you
> don't. */
> #undef HAVE_DECL_STRNLEN
> @@ -436,6 +439,9 @@
> /* Define to 1 if you have the <sys/param.h> header file. */
> #undef HAVE_SYS_PARAM_H
>
> +/* Define to 1 if you have the <sys/ptrace.h> header file. */
> +#undef HAVE_SYS_PTRACE_H
> +
> /* Define to 1 if you have the <sys/resource.h> header file. */
> #undef HAVE_SYS_RESOURCE_H
>
> @@ -847,6 +853,9 @@
> /* Define if nl_langinfo_l should be used for std::text_encoding. */
> #undef _GLIBCXX_USE_NL_LANGINFO_L
>
> +/* Define if /proc/self/status should be used for <debugging>. */
> +#undef _GLIBCXX_USE_PROC_SELF_STATUS
> +
> /* Define if pthreads_num_processors_np is available in <pthread.h>.
> */
> #undef _GLIBCXX_USE_PTHREADS_NUM_PROCESSORS_NP
>
> diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
> index 5645e991af7..55ddf36a7f1 100755
> --- a/libstdc++-v3/configure
> +++ b/libstdc++-v3/configure
> @@ -54612,6 +54612,28 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
>
>
>
> +# For std::is_debugger_present
> +case "$target_os" in
> + linux*)
> +
> +$as_echo "#define _GLIBCXX_USE_PROC_SELF_STATUS 1" >>confdefs.h
> +
> + ;;
> +esac
> +for ac_header in sys/ptrace.h debugapi.h
> +do :
> + as_ac_Header=`$as_echo "ac_cv_header_$ac_header" | $as_tr_sh`
> +ac_fn_c_check_header_mongrel "$LINENO" "$ac_header" "$as_ac_Header"
> "$ac_includes_default"
> +if eval test \"x\$"$as_ac_Header"\" = x"yes"; then :
> + cat >>confdefs.h <<_ACEOF
> +#define `$as_echo "HAVE_$ac_header" | $as_tr_cpp` 1
> +_ACEOF
> +
> +fi
> +
> +done
> +
> +
> # Define documentation rules conditionally.
>
> # See if makeinfo has been installed and is modern enough
> diff --git a/libstdc++-v3/configure.ac b/libstdc++-v3/configure.ac
> index ccb24a82be7..96b412fb7ae 100644
> --- a/libstdc++-v3/configure.ac
> +++ b/libstdc++-v3/configure.ac
> @@ -573,6 +573,15 @@ GLIBCXX_CHECK_FILEBUF_NATIVE_HANDLES
> # For std::text_encoding
> GLIBCXX_CHECK_TEXT_ENCODING
>
> +# For std::is_debugger_present
> +case "$target_os" in
> + linux*)
> + AC_DEFINE([_GLIBCXX_USE_PROC_SELF_STATUS],1,
> + [Define if /proc/self/status should be used for <debugging>.])
> + ;;
> +esac
> +AC_CHECK_HEADERS([sys/ptrace.h debugapi.h])
> +
> # Define documentation rules conditionally.
>
> # See if makeinfo has been installed and is modern enough
> diff --git a/libstdc++-v3/include/Makefile.am
> b/libstdc++-v3/include/Makefile.am
> index 422a0f4bd0a..94eca0b42f9 100644
> --- a/libstdc++-v3/include/Makefile.am
> +++ b/libstdc++-v3/include/Makefile.am
> @@ -67,6 +67,7 @@ std_headers = \
> ${std_srcdir}/codecvt \
> ${std_srcdir}/complex \
> ${std_srcdir}/condition_variable \
> + ${std_srcdir}/debugging \
> ${std_srcdir}/deque \
> ${std_srcdir}/execution \
> ${std_srcdir}/filesystem \
> diff --git a/libstdc++-v3/include/Makefile.in
> b/libstdc++-v3/include/Makefile.in
> index 9fd4ab4848c..299597ef657 100644
> --- a/libstdc++-v3/include/Makefile.in
> +++ b/libstdc++-v3/include/Makefile.in
> @@ -423,6 +423,7 @@ std_freestanding = \
> @GLIBCXX_HOSTED_TRUE@ ${std_srcdir}/codecvt \
> @GLIBCXX_HOSTED_TRUE@ ${std_srcdir}/complex \
> @GLIBCXX_HOSTED_TRUE@ ${std_srcdir}/condition_variable \
> +@GLIBCXX_HOSTED_TRUE@ ${std_srcdir}/debugging \
> @GLIBCXX_HOSTED_TRUE@ ${std_srcdir}/deque \
> @GLIBCXX_HOSTED_TRUE@ ${std_srcdir}/execution \
> @GLIBCXX_HOSTED_TRUE@ ${std_srcdir}/filesystem \
> diff --git a/libstdc++-v3/include/bits/version.def
> b/libstdc++-v3/include/bits/version.def
> index 683b967d54b..ea271901e5d 100644
> --- a/libstdc++-v3/include/bits/version.def
> +++ b/libstdc++-v3/include/bits/version.def
> @@ -1752,6 +1752,15 @@ ftms = {
> };
> };
>
> +ftms = {
> + name = debugging;
> + values = {
> + v = 202403;
> + cxxmin = 26;
> + extra_cond = "_GLIBCXX_USE_PROC_SELF_STATUS ||
> _GLIBCXX_HAVE_SYS_PTRACE_H || _GLIBCXX_HAVE_DEBUGAPI_H";
> + };
> +};
> +
> ftms = {
> name = fstream_native_handle;
> values = {
> diff --git a/libstdc++-v3/include/bits/version.h
> b/libstdc++-v3/include/bits/version.h
> index 4850041c0a3..50d2d604ce9 100644
> --- a/libstdc++-v3/include/bits/version.h
> +++ b/libstdc++-v3/include/bits/version.h
> @@ -1953,6 +1953,16 @@
> #endif /* !defined(__cpp_lib_unreachable) &&
> defined(__glibcxx_want_unreachable) */
> #undef __glibcxx_want_unreachable
>
> +#if !defined(__cpp_lib_debugging)
> +# if (__cplusplus > 202302L) && (_GLIBCXX_USE_PROC_SELF_STATUS ||
> _GLIBCXX_HAVE_SYS_PTRACE_H || _GLIBCXX_HAVE_DEBUGAPI_H)
> +# define __glibcxx_debugging 202403L
> +# if defined(__glibcxx_want_all) || defined(__glibcxx_want_debugging)
> +# define __cpp_lib_debugging 202403L
> +# endif
> +# endif
> +#endif /* !defined(__cpp_lib_debugging) &&
> defined(__glibcxx_want_debugging) */
> +#undef __glibcxx_want_debugging
> +
> #if !defined(__cpp_lib_fstream_native_handle)
> # if (__cplusplus > 202302L) && _GLIBCXX_HOSTED
> # define __glibcxx_fstream_native_handle 202306L
> diff --git a/libstdc++-v3/include/std/debugging
> b/libstdc++-v3/include/std/debugging
> new file mode 100644
> index 00000000000..76f81e23e72
> --- /dev/null
> +++ b/libstdc++-v3/include/std/debugging
> @@ -0,0 +1,82 @@
> +// Debugging support -*- C++ -*-
> +
> +// Copyright The GNU Toolchain Authors.
> +//
> +// This file is part of the GNU ISO C++ Library. This library is free
> +// software; you can redistribute it and/or modify it under the
> +// terms of the GNU General Public License as published by the
> +// Free Software Foundation; either version 3.
> +
> +// This library is distributed in the hope that it will be useful,
> +// but WITHOUT ANY WARRANTY; without even the implied warranty of
> +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> +// GNU General Public License for more details.
> +
> +// Under Section 7 of GPL version 3, you are granted additional
> +// permissions described in the GCC Runtime Library Exception, version
> +// 3.1, as published by the Free Software Foundation.
> +
> +// You should have received a copy of the GNU General Public License
> and
> +// a copy of the GCC Runtime Library Exception along with this
> program;
> +// see the files COPYING3 and COPYING.RUNTIME respectively. If not,
> see
> +// <http://www.gnu.org/licenses/>.
> +
> +/** @file include/debugging
> + * This is a Standard C++ Library header.
> + */
> +
> +#ifndef _GLIBCXX_DEBUGGING
> +#define _GLIBCXX_DEBUGGING 1
> +
> +#define __glibcxx_want_debugging
> +#include <bits/version.h>
> +
> +#if __cpp_lib_debugging // C++ >= 26
> +namespace std _GLIBCXX_VISIBILITY(default)
> +{
> +_GLIBCXX_BEGIN_NAMESPACE_VERSION
> +
> +/** Try to determine if the program is running under control of a
> debugger.
> + *
> + * On GNU/Linux systems this function will only return true if the
> program
> + * is being traced by another program which is known to be a debugger.
> + * This is determined by checking the command name of the tracing
> program
> + * against a list of known debuggers, such as "gdb".
> + *
> + * On other POSIX-based systems, this function will return true if the
> + * program is being traced by any other process, which means it can
> return
> + * true for non-debugger utilities such as strace.
> + *
> + * @since C++26
> + */
> +bool
> +is_debugger_present() noexcept;
> +
> +/** Stop the program with a breakpoint or debug trap.
> + *
> + * The details of how a breakpoint is implemented are
> platform-specific.
> + * Some systems provide a special instruction, such as `int3` in x86.
> + * When no more appropriate mechanism is available, this will stop the
> + * program using `__builtin_trap()`. It might not be possible for the
> + * program to continue after such a breakpoint.
> + *
> + * @since C++26
> + */
> +void
> +breakpoint() noexcept;
> +
> +/** Stop the program if it is running under control of a debugger.
> + *
> + * @since C++26
> + */
> +inline void
> +breakpoint_if_debugging() noexcept
> +{
> + if (std::is_debugger_present()) [[unlikely]]
> + breakpoint();
> +}
> +
> +_GLIBCXX_END_NAMESPACE_VERSION
> +} // namespace std
> +#endif
> +#endif // _GLIBCXX_DEBUGGING
> diff --git a/libstdc++-v3/src/c++26/Makefile.am
> b/libstdc++-v3/src/c++26/Makefile.am
> index 000ced1f501..551d08d583e 100644
> --- a/libstdc++-v3/src/c++26/Makefile.am
> +++ b/libstdc++-v3/src/c++26/Makefile.am
> @@ -35,7 +35,9 @@ else
> inst_sources =
> endif
>
> -sources = text_encoding.cc
> +sources = \
> + debugging.cc \
> + text_encoding.cc
>
> vpath % $(top_srcdir)/src/c++26
>
> diff --git a/libstdc++-v3/src/c++26/Makefile.in
> b/libstdc++-v3/src/c++26/Makefile.in
> index 77e73b2b265..1c317d6ac7c 100644
> --- a/libstdc++-v3/src/c++26/Makefile.in
> +++ b/libstdc++-v3/src/c++26/Makefile.in
> @@ -121,7 +121,7 @@ CONFIG_CLEAN_FILES =
> CONFIG_CLEAN_VPATH_FILES =
> LTLIBRARIES = $(noinst_LTLIBRARIES)
> libc__26convenience_la_LIBADD =
> -am__objects_1 = text_encoding.lo
> +am__objects_1 = debugging.lo text_encoding.lo
> am__objects_2 =
> @GLIBCXX_HOSTED_TRUE@am_libc__26convenience_la_OBJECTS = \
> @GLIBCXX_HOSTED_TRUE@ $(am__objects_1) $(am__objects_2)
> @@ -430,7 +430,10 @@ headers =
>
> # XTEMPLATE_FLAGS = -fno-implicit-templates
> @ENABLE_EXTERN_TEMPLATE_TRUE@inst_sources =
> -sources = text_encoding.cc
> +sources = \
> + debugging.cc \
> + text_encoding.cc
> +
> @GLIBCXX_HOSTED_FALSE@libc__26convenience_la_SOURCES =
> @GLIBCXX_HOSTED_TRUE@libc__26convenience_la_SOURCES = $(sources)
> $(inst_sources)
>
> diff --git a/libstdc++-v3/src/c++26/debugging.cc
> b/libstdc++-v3/src/c++26/debugging.cc
> new file mode 100644
> index 00000000000..150ac1ed2e7
> --- /dev/null
> +++ b/libstdc++-v3/src/c++26/debugging.cc
> @@ -0,0 +1,126 @@
> +// Implementation of <debugging> -*- C++ -*-
> +
> +// Copyright The GNU Toolchain Authors.
> +//
> +// This file is part of the GNU ISO C++ Library. This library is free
> +// software; you can redistribute it and/or modify it under the
> +// terms of the GNU General Public License as published by the
> +// Free Software Foundation; either version 3.
> +
> +// This library is distributed in the hope that it will be useful,
> +// but WITHOUT ANY WARRANTY; without even the implied warranty of
> +// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> +// GNU General Public License for more details.
> +
> +// Under Section 7 of GPL version 3, you are granted additional
> +// permissions described in the GCC Runtime Library Exception, version
> +// 3.1, as published by the Free Software Foundation.
> +
> +// You should have received a copy of the GNU General Public License
> and
> +// a copy of the GCC Runtime Library Exception along with this
> program;
> +// see the files COPYING3 and COPYING.RUNTIME respectively. If not,
> see
> +// <http://www.gnu.org/licenses/>.
> +
> +#include <debugging>
> +
> +#if __cpp_lib_debugging
> +
> +#if _GLIBCXX_USE_PROC_SELF_STATUS
> +# include <fstream>
> +# include <string>
> +#endif
> +
> +#if _GLIBCXX_HAVE_SYS_PTRACE_H
> +# include <sys/ptrace.h>
> +# include <errno.h>
> +#endif
> +
> +#if _GLIBCXX_HAVE_DEBUGAPI_H
> +# include <debugapi.h>
> +#endif
> +
> +_GLIBCXX_WEAK_DEFINITION
> +bool
> +std::is_debugger_present() noexcept
> +{
> +#if _GLIBCXX_HOSTED
> +# if _GLIBCXX_USE_PROC_SELF_STATUS
> + const string_view prefix = "TracerPid:\t";
> + ifstream in("/proc/self/status");
> + string line;
> + while (std::getline(in, line))
> + {
> + if (!line.starts_with(prefix))
> + continue;
> +
> + string_view tracer = line;
> + tracer.remove_prefix(prefix.size());
> + if (tracer.size() == 1 && tracer[0] == '0') [[likely]]
> + return false; // Not being traced.
> +
> + in.close();
> + string_view cmd;
> + string proc_dir = "/proc/" + string(tracer) + '/';
> + in.open(proc_dir + "comm"); // since Linux 2.6.33
> + if (std::getline(in, line)) [[likely]]
> + cmd = line;
> + else
> + {
> + in.close();
> + in.open(proc_dir + "cmdline");
> + if (std::getline(in, line))
> + cmd = line.c_str(); // Only up to first '\0'
> + else
> + return false;
> + }
> +
> + for (auto i : {"gdb", "lldb"}) // known debuggers
> + if (cmd.ends_with(i))
> + return true;
> +
> + // We found the TracerPid line, no need to do any more work.
> + return false;
> + }
> +# endif
> +# if _GLIBCXX_HAVE_SYS_PTRACE_H
> + if (::ptrace(PTRACE_TRACEME, 0, 1, 0) == -1)
> + return errno == EPERM;
> +# endif
> +# if _GLIBCXX_HAVE_DEBUGAPI_H && defined(_WIN32) &&
> !defined(__CYGWIN__)
> + return IsDebuggerPresent();
> +# endif
> +#endif // HOSTED
> + return false;
> +}
> +
> +void
> +std::breakpoint() noexcept
> +{
> +#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");
Worth noting, currently gcc has some bugs around its handling of int3,
https://sourceware.org/bugzilla/show_bug.cgi?id=31194
int3;nop seems to work around it okay. __builtin_debugtrap() of clang
does run into the same issues.
> +#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.
> +
> +#endif // __cpp_lib_debugging
> diff --git
> a/libstdc++-v3/testsuite/19_diagnostics/debugging/breakpoint.cc
> b/libstdc++-v3/testsuite/19_diagnostics/debugging/breakpoint.cc
> new file mode 100644
> index 00000000000..ee572dc9424
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/19_diagnostics/debugging/breakpoint.cc
> @@ -0,0 +1,9 @@
> +// { dg-do run { target c++26 xfail c++26 } }
> +// { dg-options "-lstdc++exp" }
> +// { dg-require-cpp-feature-test __cpp_lib_debugging }
> +#include <debugging>
> +
> +int main()
> +{
> + std::breakpoint();
> +}
> diff --git
> a/libstdc++-v3/testsuite/19_diagnostics/debugging/breakpoint_if_debugging.cc
> b/libstdc++-v3/testsuite/19_diagnostics/debugging/breakpoint_if_debugging.cc
> new file mode 100644
> index 00000000000..02ac245daaf
> --- /dev/null
> +++
> b/libstdc++-v3/testsuite/19_diagnostics/debugging/breakpoint_if_debugging.cc
> @@ -0,0 +1,9 @@
> +// { dg-do run { target c++26 } }
> +// { dg-options "-lstdc++exp" }
> +// { dg-require-cpp-feature-test __cpp_lib_debugging }
> +#include <debugging>
> +
> +int main()
> +{
> + std::breakpoint_if_debugging();
> +}
Regards,
Peter D.
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