On Wed, 10 Oct 2018, Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote: > On Wed, Oct 10, 2018 at 1:30 PM Michal Wajdeczko > <michal.wajdeczko@xxxxxxxxx> wrote: >> >> On Wed, 10 Oct 2018 14:01:40 +0200, Jani Nikula >> <jani.nikula@xxxxxxxxxxxxxxx> wrote: >> >> > On Tue, 09 Oct 2018, Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote: >> >> On Tue, Oct 9, 2018 at 10:14 AM Nathan Chancellor >> >> <natechancellor@xxxxxxxxx> wrote: >> >>> >> >>> 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. >> >> >> >> Thanks Nathan for the patch. To provide more context, Clang does >> >> semantic analysis before optimization, where as GCC does these >> >> together (IIUC). So the above link error is from the naked >> >> BUILD_BUG(). Clang can't evaluate the __builtin_strcmp's statically >> >> until inlining has occurred, but that optimization happens after >> >> semantic analysis. To do the inlining before semantic analysis, we >> >> MUST leverage the preprocessor, which runs before the compiler starts >> >> doing semantic analysis. I suspect this code is not valid for GCC >> >> unless optimizations are enabled (the kernel only does compile with >> >> optimizations turned on). This change allows us to build this >> >> translation unit with Clang. >> >> >> >> Acked-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> >> >> (Note: this is the change I suggested, so not sure whether Acked-by or >> >> Reviewed-by is more appropriate). >> > >> > *Sad trombone* >> > >> > I'd rather see us converting more macros to static inlines than the >> > other way round. >> > >> > I'll let others chime in if they have any better ideas, otherwise I'll >> > apply this one. >> >> Option 1: Just drop BUILD_BUG() from _print_param() function. > > I was also thinking of this. So does this fix the issue? 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); } /** --- > >> >> Option 2: Use aliases instead of real types in param() macros. > > Will that affect other users of I915_PARAMS_FOR_EACH than _print_param? > > Either way, thanks for the help towards resolving this! We appreciate it! > >> >> Aliases can be same as in linux/moduleparam.h (charp|int|uint|bool) >> We can convert aliases back to real types but it will also allow >> to construct proper names for dedicated functions - see [1] >> >> Michal >> >> [1] https://patchwork.freedesktop.org/patch/255928/ I can't find this on the list; was this sent just to patchwork or what? BR, Jani. >> >> >> > >> > BR, >> > Jani. >> > >> >> >> >>> >> >>> 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@xxxxxxxxxx> >> >>> Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx> >> >>> --- >> >>> 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 >> >>> -- Jani Nikula, Intel Open Source Graphics Center _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
