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.
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. RFC. This requires a MISRA change, as it currently manifests as a R1.1 violation. Nevertheless, I think we want to start using in places where we currently use typeof(expression of <initilaiser>). Eclair run on this patch (expecting a failure): https://gitlab.com/xen-project/hardware/xen-staging/-/pipelines/1800631949 Min toolchain check: https://godbolt.org/z/f9WjooPYj GCC Manual: https://www.gnu.org/software/c-intro-and-ref/manual/html_node/Auto-Type.html --- xen/include/xen/macros.h | 14 +++++++------- 1 file changed, 7 insertions(+), 7 deletions(-) diff --git a/xen/include/xen/macros.h b/xen/include/xen/macros.h index cd528fbdb127..b5e5ff4b1c2f 100644 --- a/xen/include/xen/macros.h +++ b/xen/include/xen/macros.h @@ -71,18 +71,18 @@ /* Hide a value from the optimiser. */ #define HIDE(x) \ ({ \ - typeof(x) _x = (x); \ + __auto_type _x = (x); \ asm volatile ( "" : "+r" (_x) ); \ _x; \ }) #define ABS(x) ({ \ - typeof(x) x_ = (x); \ + __auto_type x_ = (x); \ (x_ < 0) ? -x_ : x_; \ }) #define SWAP(a, b) \ - do { typeof(a) t_ = (a); (a) = (b); (b) = t_; } while ( 0 ) + do { __auto_type t_ = (a); (a) = (b); (b) = t_; } while ( 0 ) #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]) + __must_be_array(x)) @@ -110,15 +110,15 @@ */ #define min(x, y) \ ({ \ - const typeof(x) _x = (x); \ - const typeof(y) _y = (y); \ + const __auto_type _x = (x); \ + const __auto_type _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_type _x = (x); \ + const __auto_type _y = (y); \ (void)(&_x == &_y); /* typecheck */ \ _x > _y ? _x : _y; \ }) base-commit: 78ce2be733b1e45e2e190c1765fe31da318d435f -- 2.39.5
