Re: [PATCH v3 2/7] gdb: fail configure if Python version is too old for limited API

[Matthieu Longo <matthieu.longo@arm.com>]

On 31/03/2026 11:16, Matthieu Longo wrote:
> On 24/03/2026 18:53, Tom Tromey wrote:
>>>>>>> Matthieu Longo <matthieu.longo@arm.com> writes:
>>
>>> GDB can be built against the Python limited API using the configure
>>> flag '--enable-py-limited-api=yes'. This flag is currently experimental,
>>> and the build is not yet fully successful. Today, the minimum required
>>> Python version for this option is 3.11. This requirement is not final
>>> and will be raised to a later version as the migration progresses.
>>
>>> However, the configure script does not currently report an error if an
>>> older version of Python is used. Instead, the build fails later with
>>> numerous errors that are difficult to relate to Python limited API
>>> compatiblity.
>>
>>> This patch adds a version check when '--enable-py-limited-api=yes' is
>>> specified, ensuring that the provided Python version meets the minimum
>>> requirements for the limited API support. If it does not, configure will
>>> now fail with a clear error message.
>>
>> Sorry about the delay on this.
>>
>> I'm a bit worried about adding a bunch of new python-related configury.
>> Like are we sure it will agree with what's already in there?  As in,
>> picking up the same version from the same place, etc?  For instance does
>> this new code respect --with-python-libdir?
>>
>> I wonder if instead there could just be a new compile test that is run
>> when --enable-py-limited-api is used.  This test could just check
>> PY_VERSION_HEX and #error on failure.
>>
>> Wouldn't that have the same effect but without adding a ton of new code?
>>
>> TBH I'd even be happy with not doing this check in configure at all and
>> saying that if you specify --enable-py-limited-api then you should know
>> what you're doing and if you mess up you'll just get compile-time
>> errors.  That is, stick the check in python-internal.h.
>>
>> Tom
> 
> So I followed your advice and added a compile test checking PY_VERSION_HEX and #erroring on failure.
> Here below is the new patch that I posted here to avoid a new revision.
> 
> Matthieu
> 
> 
> diff --git a/gdb/configure b/gdb/configure
> index 12c54521682..16580e4af7d 100755
> --- a/gdb/configure
> +++ b/gdb/configure
> @@ -28507,6 +28507,7 @@ fi
>       # do except assume that the compiler will be able to find those files.
>       python_includes=
>       python_libs=
> +    python_prefix=
>       have_python_config=no
>     fi
> 
> @@ -28743,6 +28744,7 @@ else
>   fi
> 
> 
> +
>   # Check whether to build GDB against Python limited C API.
>   # Check whether --enable-py-limited-api was given.
>   if test "${enable_py_limited_api+set}" = set; then :
> @@ -28763,11 +28765,46 @@ fi
>   if test "$enable_py_limited_api" = yes; then
>     # The minimal Python limited API version is currently set to 3.11 for the
>     # support of PyBuffer_FillInfo and PyBuffer_Release.
> -  # The choice of the minimal version for the Python limited API won't be frozen
> -  # until the end of the migration.
> +  # The choice of the minimal version for the Python limited API won't be
> +  # frozen until the end of the migration.
> +  old_CFLAGS="$CFLAGS"
> +  CFLAGS="$CFLAGS $PYTHON_CFLAGS"
> +  old_CPPFLAGS="$CPPFLAGS"
> +  CPPFLAGS="$CPPFLAGS $PYTHON_CPPFLAGS"
> +  old_LIBS="$LIBS"
> +  LIBS="$LIBS $PYTHON_LIBS"
> +  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
> +/* end confdefs.h.  */
> +#include <Python.h>
> +#ifndef PY_VERSION_HEX
> +#error "PY_VERSION_HEX is not defined"
> +#endif
> +#if PY_VERSION_HEX < 0x030b0000
> +#error "Python limited API support requires at least Python version 3.11"
> +#endif
> +
> +int
> +main ()
> +{
> +
> +  ;
> +  return 0;
> +}
> +_ACEOF
> +if ac_fn_c_try_compile "$LINENO"; then :
> 
>   $as_echo "#define Py_LIMITED_API 0x030b0000" >>confdefs.h
> 
> +
> +else
> +
> +      as_fn_error $? "Python limited API support requires at least Python version 3.11" "$LINENO" 5
> +
> +fi
> +rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
> +  CFLAGS="$old_CFLAGS"
> +  CPPFLAGS="$old_CPPFLAGS"
> +  LIBS="$old_LIBS"
>   fi
> 
>   # -------------------- #
> diff --git a/gdb/configure.ac b/gdb/configure.ac
> index cf8078e1d89..c6b0653e3b0 100644
> --- a/gdb/configure.ac
> +++ b/gdb/configure.ac
> @@ -933,6 +933,7 @@ else
>       # do except assume that the compiler will be able to find those files.
>       python_includes=
>       python_libs=
> +    python_prefix=
>       have_python_config=no
>     fi
> 
> @@ -1062,6 +1063,13 @@ AC_SUBST(PYTHON_CPPFLAGS)
>   AC_SUBST(PYTHON_LIBS)
>   AM_CONDITIONAL(HAVE_PYTHON, test "${have_libpython}" != no)
> 
> +dnl Use --enable-py-limited-api to enable the build of GDB against the Python
> +dnl limited API.
> +dnl
> +dnl no -   Disable the Python limited API.
> +dnl yes -  Use the Python limited API to build GDB, error if the selected
> +dnl        version of Python is not compatible with the Python limited API.
> +
>   # Check whether to build GDB against Python limited C API.
>   AC_ARG_ENABLE([py-limited-api],
>                [AS_HELP_STRING([--enable-py-limited-api],
> @@ -1072,10 +1080,31 @@ AC_ARG_ENABLE([py-limited-api],
>   if test "$enable_py_limited_api" = yes; then
>     # The minimal Python limited API version is currently set to 3.11 for the
>     # support of PyBuffer_FillInfo and PyBuffer_Release.
> -  # The choice of the minimal version for the Python limited API won't be frozen
> -  # until the end of the migration.
> -  AC_DEFINE(Py_LIMITED_API, 0x030b0000,
> -           [Define if GDB should be built against the Python limited C API.])
> +  # The choice of the minimal version for the Python limited API won't be
> +  # frozen until the end of the migration.
> +  old_CFLAGS="$CFLAGS"
> +  CFLAGS="$CFLAGS $PYTHON_CFLAGS"
> +  old_CPPFLAGS="$CPPFLAGS"
> +  CPPFLAGS="$CPPFLAGS $PYTHON_CPPFLAGS"
> +  old_LIBS="$LIBS"
> +  LIBS="$LIBS $PYTHON_LIBS"
> +  AC_COMPILE_IFELSE([AC_LANG_PROGRAM(
> +    [[#include <Python.h>
> +#ifndef PY_VERSION_HEX
> +#error "PY_VERSION_HEX is not defined"
> +#endif
> +#if PY_VERSION_HEX < 0x030b0000
> +#error "Python limited API support requires at least Python version 3.11"
> +#endif
> +    ]],[[]])],
> +    [AC_DEFINE(Py_LIMITED_API, 0x030b0000,
> +      [Define if GDB should be built against the Python limited C API.])
> +    ],[
> +      AC_MSG_ERROR([Python limited API support requires at least Python version 3.11])
> +    ])
> +  CFLAGS="$old_CFLAGS"
> +  CPPFLAGS="$old_CPPFLAGS"
> +  LIBS="$old_LIBS"
>   fi
> 
>   # -------------------- #

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