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Re: [PATCH 09/12] Eclair: deviate BUILD_ERROR() wrt rule 2.1 and introduce variants
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
- Date: Sat, 29 Aug 2026 16:04:42 +0200
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- Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Roger Pau Monné <roger@xxxxxxxxxxxxxx>
- Delivery-date: Sat, 29 Aug 2026 14:04:51 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 2026-08-28 09:04, Jan Beulich wrote:
BUILD_ERROR() is even stronger a guard than assertions in general, and
ASSERT_UNREACHABLE() (or BUG()) in particular. Deviate it just like
those
to allow use for marking unreachable portions of code.
In some cases code being unreachable is dependent upon configuration.
Introduce two variants, as constructs like
if ( IS_ENABLED(CONFIG_...) )
BUILD_ERROR("...");
results in the if() still being reported as unreachable. Sadly these
two
new macros introduce a new 20.12 violation each, which hence also needs
deviating.
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Reviewed-by: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>
Presumably you did not fold at least one of the following patches where
the construct is actually used into this one to separate concerns?
--- a/automation/eclair_analysis/ECLAIR/deviations.ecl
+++ b/automation/eclair_analysis/ECLAIR/deviations.ecl
@@ -19,6 +19,7 @@ Constant expressions and unreachable bra
-doc_begin="Unreachability inside an ASSERT_UNREACHABLE() and
analogous macro calls is deliberate and safe."
-config=MC3A2.R2.1,reports+={deliberate,
"any_area(any_loc(any_exp(macro(name(ASSERT_UNREACHABLE||PARSE_ERR_RET||PARSE_ERR||FAIL_MSR||FAIL_CPUID)))))"}
+-config=MC3A2.R2.1,reports+={deliberate,
"any_area(any_loc(any_exp(macro(^BUILD_ERROR(|_IF(|_NOT))$))))"}
-doc_end
-doc_begin="The asm-offset files are not linked deliberately, since
they are used to generate definitions for asm modules."
@@ -667,6 +668,7 @@ deliberate."
to the # or ## operators within the following macros are deliberate,
to provide
useful diagnostic messages to the user."
-config=MC3A2.R20.12,macros+={deliberate,
"name(ASSERT||BUILD_BUG_ON||BUILD_BUG_ON_ZERO||RUNTIME_CHECK)"}
+-config=MC3A2.R20.12,macros+={deliberate,
"^BUILD_ERROR(|_IF(|_NOT))$"}
-doc_end
-doc_begin="The helper macro GENERATE_CASE may use a macro parameter
for ordinary
--- a/xen/include/xen/macros.h
+++ b/xen/include/xen/macros.h
@@ -64,6 +64,21 @@
*/
#define BUILD_ERROR(msg) asm ( ".error \"" msg "\"" )
+/*
+ * Like above, but conditional upon @cfg (not) being enabled. @cfg
must be
+ * suitable to pass to IS_ENABLED().
+ */
+#define BUILD_ERROR_IF(cfg) \
+ (IS_ENABLED(cfg) \
+ ? ({ BUILD_ERROR( #cfg " unexpectedly enabled"); }) \
+ : (void)0)
+
+#define BUILD_ERROR_IF_NOT(cfg) \
+ (!IS_ENABLED(cfg) \
+ ? ({ BUILD_ERROR( #cfg " unexpectedly disabled"); }) \
+ : (void)0)
+
+
/* Hide a value from the optimiser. */
#define HIDE(x) \
({ \
--
Nicola Vetrini, B.Sc.
Software Engineer
BUGSENG (https://bugseng.com)
LinkedIn: https://www.linkedin.com/in/nicola-vetrini-a42471253
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