On 2025-05-05 14:46, Andrew Cooper wrote:
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
Hi,
to make the analysis pass you need a couple of hunks in
eclair_analysis/ECLAIR/toolchain.ecl:
-name_selector+={auto_type, "^__auto_type$"}
and add auto_type to the STD.tokenext config below around line 25, then
later
-name_selector+={ext_auto_type, "^ext_auto_type$"}
and add "ext_auto_type" to the -config lines below
around line 125, along with a reference to the gcc docs above the
configurations and in C-language-toolchain.rst
This is an extension, so it's usable without further MISRA impact.
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
--
Nicola Vetrini, B.Sc.
Software Engineer
BUGSENG (https://bugseng.com)
LinkedIn: https://www.linkedin.com/in/nicola-vetrini-a42471253
