drm/i915: Ensure _print_param() builds with Clang

jnikula · jnikula · commit 7b3e51dd439b · 2018-10-17T09:55:21.000+03:00
When building the kernel with Clang with defconfig and CONFIG_64BIT disabled, vmlinux fails to link because of the BUILD_BUG in _print_param. ld: drivers/gpu/drm/i915/i915_params.o: in function `i915_params_dump': i915_params.c:(.text+0x56): undefined reference to `__compiletime_assert_191' This function is semantically invalid unless the code is first inlined then constant folded, which doesn't work for Clang because semantic analysis happens before optimization/inlining. [The above written by Nathan Chancellor <natechancellor@gmail.com>] Use WARN_ONCE() instead of BUILD_BUG() to avoid the problem. The WARN_ONCE() should get optimized away unless there's a type that's not handled by _print_param(). References: ClangBuiltLinux#191 References: http://mid.mail-archive.com/20181009171401.14980-1-natechancellor@gmail.com Cc: Nick Desaulniers <ndesaulniers@google.com> Cc: Nathan Chancellor <natechancellor@gmail.com> Cc: Chris Wilson <chris@chris-wilson.co.uk> Reported-by: Nick Desaulniers <ndesaulniers@google.com> Reported-by: Nathan Chancellor <natechancellor@gmail.com> Tested-by: Nathan Chancellor <natechancellor@gmail.com> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Signed-off-by: Jani Nikula <jani.nikula@intel.com> Link: https://patchwork.freedesktop.org/patch/msgid/20181016122938.18757-1-jani.nikula@intel.com
diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
@@ -184,7 +184,8 @@ static __always_inline void _print_param(struct drm_printer *p,
 	else if (!__builtin_strcmp(type, "char *"))
 		drm_printf(p, "i915.%s=%s\n", name, *(const char **)x);
 	else
-		BUILD_BUG();
+		WARN_ONCE(1, "no printer defined for param type %s (i915.%s)\n",
+			  type, name);
 }
 
 /**

Original file line number	Diff line number	Diff line change
`@@ -184,7 +184,8 @@ static __always_inline void _print_param(struct drm_printer *p,`
`184`	`184`	`else if (!__builtin_strcmp(type, "char *"))`
`185`	`185`	`drm_printf(p, "i915.%s=%s\n", name, (const char *)x);`
`186`	`186`	`else`
`187`		`- BUILD_BUG();`
	`187`	`+ WARN_ONCE(1, "no printer defined for param type %s (i915.%s)\n",`
	`188`	`+ type, name);`
`188`	`189`	`}`
`189`	`190`
`190`	`191`	`/**`