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Subject[PATCH] drm/i915: Convert _print_param to a macro
Date
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. Converting this function
to a macro avoids this problem and allows Clang to properly remove the
BUILD_BUG during optimization.

The output of 'objdump -D' is identically before and after this change
for GCC regardless of if CONFIG_64BIT is set and allows Clang to link
the kernel successfully with or without CONFIG_64BIT set.

Link: https://github.com/ClangBuiltLinux/linux/issues/191
Suggested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
---
drivers/gpu/drm/i915/i915_params.c | 29 +++++++++++++----------------
1 file changed, 13 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
index 295e981e4a39..a0f20b9b6f2d 100644
--- a/drivers/gpu/drm/i915/i915_params.c
+++ b/drivers/gpu/drm/i915/i915_params.c
@@ -174,22 +174,19 @@ i915_param_named(enable_dpcd_backlight, bool, 0600,
i915_param_named(enable_gvt, bool, 0400,
"Enable support for Intel GVT-g graphics virtualization host support(default:false)");

-static __always_inline void _print_param(struct drm_printer *p,
- const char *name,
- const char *type,
- const void *x)
-{
- if (!__builtin_strcmp(type, "bool"))
- drm_printf(p, "i915.%s=%s\n", name, yesno(*(const bool *)x));
- else if (!__builtin_strcmp(type, "int"))
- drm_printf(p, "i915.%s=%d\n", name, *(const int *)x);
- else if (!__builtin_strcmp(type, "unsigned int"))
- drm_printf(p, "i915.%s=%u\n", name, *(const unsigned int *)x);
- else if (!__builtin_strcmp(type, "char *"))
- drm_printf(p, "i915.%s=%s\n", name, *(const char **)x);
- else
- BUILD_BUG();
-}
+#define _print_param(p, name, type, x) \
+do { \
+ if (!__builtin_strcmp(type, "bool")) \
+ drm_printf(p, "i915.%s=%s\n", name, yesno(*(const bool *)x)); \
+ else if (!__builtin_strcmp(type, "int")) \
+ drm_printf(p, "i915.%s=%d\n", name, *(const int *)x); \
+ else if (!__builtin_strcmp(type, "unsigned int")) \
+ drm_printf(p, "i915.%s=%u\n", name, *(const unsigned int *)x); \
+ else if (!__builtin_strcmp(type, "char *")) \
+ drm_printf(p, "i915.%s=%s\n", name, *(const char **)x); \
+ else \
+ BUILD_BUG(); \
+} while (0)

/**
* i915_params_dump - dump i915 modparams
--
2.19.0
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