In macros it is common to declare local variables using typeof(param) in order to ensure that side effects are only evaluated once. A consequence of this is double textural expansion of the parameter, which can get out of hand very quickly with nested macros.
In C23, the auto keyword has been repurposed to perform type inference. A GCC extension, __auto_type, is now avaialble in the new toolchain baseline and avoids the double textural expansion. Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com> --- CC: Anthony PERARD <anthony.per...@vates.tech> CC: Michal Orzel <michal.or...@amd.com> CC: Jan Beulich <jbeul...@suse.com> CC: Julien Grall <jul...@xen.org> CC: Roger Pau Monné <roger....@citrix.com> CC: Stefano Stabellini <sstabell...@kernel.org> CC: Roberto Bagnara <roberto.bagn...@bugseng.com> CC: Nicola Vetrini <nicola.vetr...@bugseng.com> CC: consult...@bugseng.com <consult...@bugseng.com> The resulting build is identical. v2: * Use auto directly * Eclair configuration https://gitlab.com/xen-project/hardware/xen-staging/-/pipelines/1985289434 --- automation/eclair_analysis/ECLAIR/toolchain.ecl | 11 +++++++++-- docs/misra/C-language-toolchain.rst | 2 ++ xen/include/xen/compiler.h | 14 ++++++++++++++ xen/include/xen/macros.h | 14 +++++++------- 4 files changed, 32 insertions(+), 9 deletions(-) diff --git a/automation/eclair_analysis/ECLAIR/toolchain.ecl b/automation/eclair_analysis/ECLAIR/toolchain.ecl index 842f8377e561..125f99a06583 100644 --- a/automation/eclair_analysis/ECLAIR/toolchain.ecl +++ b/automation/eclair_analysis/ECLAIR/toolchain.ecl @@ -15,6 +15,7 @@ __alignof__, __alignof: see Sections \"6.48 Alternate Keywords\" and \"6.44 Determining the Alignment of Functions, Types or Variables\" of "GCC_MANUAL". asm, __asm__: see Sections \"6.48 Alternate Keywords\" and \"6.47 How to Use Inline Assembly Language in C Code\" of "GCC_MANUAL". __attribute__: see Section \"6.39 Attribute Syntax\" of "GCC_MANUAL". + __auto_type: see Section \"6.7 Referring to a Type with typeof\" of "GCC_MANUAL". __builtin_offsetof: see Section \"6.53 Support for offsetof\" of "GCC_MANUAL". __builtin_types_compatible_p: see Section \"6.59 Other Built-in Functions Provided by GCC\" of "GCC_MANUAL". __builtin_va_arg: non-documented GCC extension. @@ -26,6 +27,7 @@ -name_selector+={alignof, "^(__alignof__|__alignof)$"} -name_selector+={asm, "^(__asm__|asm)$"} -name_selector+={attribute, "^__attribute__$"} +-name_selector+={auto_type, "^__auto_type$"} -name_selector+={builtin_offsetof, "^__builtin_offsetof$"} -name_selector+={builtin_types_p, "^__builtin_types_compatible_p$"} -name_selector+={builtin_va_arg, "^__builtin_va_arg$"} @@ -39,6 +41,7 @@ "alignof|| asm|| attribute|| +auto_type|| builtin_offsetof|| builtin_types_p|| builtin_va_arg|| @@ -114,6 +117,7 @@ volatile" -doc_end -doc_begin=" + ext_auto_type: see Section \"6.7 Referring to a Type with typeof\" of "GCC_MANUAL". ext_c_missing_varargs_arg: see Section \"6.21 Macros with a Variable Number of Arguments\" of "GCC_MANUAL". ext_enum_value_not_int: non-documented GCC extension. ext_flexible_array_in_array: see Section \"6.18 Arrays of Length Zero\" of "GCC_MANUAL". @@ -126,6 +130,7 @@ volatile" ext_return_has_void_expr: see the documentation for -Wreturn-type in Section \"3.8 Options to Request or Suppress Warnings\" of "GCC_MANUAL". ext_sizeof_alignof_void_type: see Section \"6.24 Arithmetic on void- and Function-Pointers\" of "GCC_MANUAL". " +-name_selector+={ext_auto_type, "^ext_auto_type$"} -name_selector+={ext_c_missing_varargs_arg, "^ext_c_missing_varargs_arg$"} -name_selector+={ext_enum_value_not_int, "^ext_enum_value_not_int$"} -name_selector+={ext_flexible_array_in_array, "^ext_flexible_array_in_array$"} @@ -139,7 +144,8 @@ volatile" -name_selector+={ext_sizeof_alignof_void_type, "^ext_sizeof_alignof_void_type$"} -config=STD.diag,behavior+={c99,GCC_ARM64, -"ext_c_missing_varargs_arg|| +"ext_auto_type|| +ext_c_missing_varargs_arg|| ext_forward_ref_enum_def|| ext_gnu_array_range|| ext_gnu_statement_expr_macro|| @@ -149,7 +155,8 @@ ext_return_has_void_expr|| ext_sizeof_alignof_void_type" } -config=STD.diag,behavior+={c99,GCC_X86_64, -"ext_c_missing_varargs_arg|| +"ext_auto_type|| +ext_c_missing_varargs_arg|| ext_enum_value_not_int|| ext_flexible_array_in_array|| ext_flexible_array_in_struct|| diff --git a/docs/misra/C-language-toolchain.rst b/docs/misra/C-language-toolchain.rst index cb81f5c09872..635936004554 100644 --- a/docs/misra/C-language-toolchain.rst +++ b/docs/misra/C-language-toolchain.rst @@ -94,6 +94,8 @@ The table columns are as follows: see Sections "6.48 Alternate Keywords" and "6.44 Determining the Alignment of Functions, Types or Variables" of GCC_MANUAL. __attribute__: see Section "6.39 Attribute Syntax" of GCC_MANUAL. + __auto_type: + see Section "6.7 Referring to a Type with typeof" of GCC_MANUAL. __builtin_types_compatible_p: see Section "6.59 Other Built-in Functions Provided by GCC" of GCC_MANUAL. __builtin_va_arg: diff --git a/xen/include/xen/compiler.h b/xen/include/xen/compiler.h index 88bf26bc5109..38ef5d82ad95 100644 --- a/xen/include/xen/compiler.h +++ b/xen/include/xen/compiler.h @@ -64,6 +64,20 @@ # define asm_inline asm #endif +/* + * In C23, the auto keyword has been repurposed to perform type inference. + * + * This behaviour is available via the __auto_type extension in supported + * toolchains. + * + * https://www.gnu.org/software/c-intro-and-ref/manual/html_node/Auto-Type.html + * https://clang.llvm.org/docs/LanguageExtensions.html#auto-type + */ +#if !defined(__STDC_VERSION__) || __STDC_VERSION__ < 202311L +/* SAF-3-safe MISRA C Rule 20.4: Giving the keyword it's C23 meaning. */ +#define auto __auto_type +#endif + /* * Add the pseudo keyword 'fallthrough' so case statement blocks * must end with any of these keywords: diff --git a/xen/include/xen/macros.h b/xen/include/xen/macros.h index f9ccde86fb23..ceca2e4a1bf1 100644 --- a/xen/include/xen/macros.h +++ b/xen/include/xen/macros.h @@ -63,18 +63,18 @@ /* Hide a value from the optimiser. */ #define HIDE(x) \ ({ \ - typeof(x) _x = (x); \ + auto _x = (x); \ asm volatile ( "" : "+r" (_x) ); \ _x; \ }) #define ABS(x) ({ \ - typeof(x) x_ = (x); \ + auto x_ = (x); \ (x_ < 0) ? -x_ : x_; \ }) #define SWAP(a, b) \ - do { typeof(a) t_ = (a); (a) = (b); (b) = t_; } while ( 0 ) + do { auto t_ = (a); (a) = (b); (b) = t_; } while ( 0 ) #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]) + __must_be_array(x)) @@ -102,15 +102,15 @@ */ #define min(x, y) \ ({ \ - const typeof(x) _x = (x); \ - const typeof(y) _y = (y); \ + const auto _x = (x); \ + const auto _y = (y); \ (void)(&_x == &_y); /* typecheck */ \ _x < _y ? _x : _y; \ }) #define max(x, y) \ ({ \ - const typeof(x) _x = (x); \ - const typeof(y) _y = (y); \ + const auto _x = (x); \ + const auto _y = (y); \ (void)(&_x == &_y); /* typecheck */ \ _x > _y ? _x : _y; \ }) base-commit: b2c0dc44b37516b758c38de04c61ad295ac0dff2 -- 2.39.5
