[Intel-gfx] [PATCH 1/2] drm/i915: Ensure _print_param() builds with Clang

[Jani Nikula]

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 at 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: https://github.com/ClangBuiltLinux/linux/issues/191
References: http://mid.mail-archive.com/20181009171401.14980-1-natechancellor@gmail.com
Cc: Nick Desaulniers <ndesaulniers at google.com>
Cc: Nathan Chancellor <natechancellor at gmail.com>
Cc: Chris Wilson <chris at chris-wilson.co.uk>
Reported-by: Nick Desaulniers <ndesaulniers at google.com>
Reported-by: Nathan Chancellor <natechancellor at gmail.com>
Signed-off-by: Jani Nikula <jani.nikula at intel.com>
---
 drivers/gpu/drm/i915/i915_params.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
index bd6bd8879cab..8d71886b5f03 100644
--- 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);
 }
 
 /**
-- 
2.11.0