Re: [PATCH] sparc64: Add preprocessor symbols for PAGE_* pgprot_t values.
From: Clemens Ladisch Date: Mon, 03 Nov 2014 10:44:40 +0100 > David Miller wrote: >> I'd also rather the kernel use Kconfig based symbols to detect for >> arch availability of feature X or Y, assuming things are CPP symbols >> is very fragile at best. > > It is certainly possible to use Kconfig-based symbols. However, this > would have its own fragility: adding, e.g., PAGE_KERNEL_SO to an arch > requires that one remembers to update Kconfig, and if one forgets, > a check like this: > > #ifndef CONFIG_ARCH_HAS_PAGE_KERNEL_RO > #define PAGE_KERNEL_RO PAGE_KERNEL /* fallback for this code */ > #endif > > will not detect the error on sparc64 (if PAGE_KERNEL_RO were a CPP > symbol, the compiler would complain about the redefinition). > > So even if PAGE_KERNEL_RO is a variable, making it into a CPP symbol > is beneficial. And once it is a CPP symbol, introducing a separate > Kconfig-based symbol is not necessary and just increases the chances > of an error. I'd rather code then use the symbol unconditionally, and we declare that it's something every architecture must provide in some shape or form. This CPP check business is fragile as hell and I'm not going to promote it in the architectures I maintainer by applying patches like your's. Sorry. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] sparc64: Add preprocessor symbols for PAGE_* pgprot_t values.
David Miller wrote: >> Kernel code assumes that the PAGE_* values are preprocessor symbols, and >> that therefore arch support can be checked for with #ifdef. >> >> At the moment, sparc64 does not implement any of the symbols checked >> for, so these checks happen to work. >> >> To prevent potential breakage when another #ifdef check is added or when >> sparc64 implements another PAGE_ value, make such #ifdef checks work by >> adding preprocessor symbols on top of the PAGE_* variables. >> >> Signed-off-by: Clemens Ladisch > > "This change actually doesn't have any effect, and doesn't matter, > so let's make this change." > > I really don't buy this. At the moment, sparc64 does not support symbols such as PAGE_KERNEL_RO, and has no mechanism for arch-independent code to detect this. Some code tries anyway: $ git grep '#ifn\?def PAGE_KERNEL_' drivers/base/firmware_class.c:#ifndef PAGE_KERNEL_RO drivers/staging/comedi/comedi_buf.c:#ifdef PAGE_KERNEL_NOCACHE mm/nommu.c:#ifndef PAGE_KERNEL_EXEC mm/vmalloc.c:#ifndef PAGE_KERNEL_EXEC I don't want to add more such code to the kernel without a guarantee that it actually works, or without replacing it with some other kind of check that does work. > I'd also rather the kernel use Kconfig based symbols to detect for > arch availability of feature X or Y, assuming things are CPP symbols > is very fragile at best. It is certainly possible to use Kconfig-based symbols. However, this would have its own fragility: adding, e.g., PAGE_KERNEL_SO to an arch requires that one remembers to update Kconfig, and if one forgets, a check like this: #ifndef CONFIG_ARCH_HAS_PAGE_KERNEL_RO #define PAGE_KERNEL_RO PAGE_KERNEL /* fallback for this code */ #endif will not detect the error on sparc64 (if PAGE_KERNEL_RO were a CPP symbol, the compiler would complain about the redefinition). So even if PAGE_KERNEL_RO is a variable, making it into a CPP symbol is beneficial. And once it is a CPP symbol, introducing a separate Kconfig-based symbol is not necessary and just increases the chances of an error. Regards, Clemens -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Re: [PATCH] sparc64: Add preprocessor symbols for PAGE_* pgprot_t values.
From: Clemens Ladisch Date: Sun, 02 Nov 2014 21:15:12 +0100 > Kernel code assumes that the PAGE_* values are preprocessor symbols, and > that therefore arch support can be checked for with #ifdef. > > At the moment, sparc64 does not implement any of the symbols checked > for, so these checks happen to work. > > To prevent potential breakage when another #ifdef check is added or when > sparc64 implements another PAGE_ value, make such #ifdef checks work by > adding preprocessor symbols on top of the PAGE_* variables. > > Signed-off-by: Clemens Ladisch "This change actually doesn't have any effect, and doesn't matter, so let's make this change." I really don't buy this. I'd also rather the kernel use Kconfig based symbols to detect for arch availability of feature X or Y, assuming things are CPP symbols is very fragile at best. I'm not applying this, sorry. I mean, you didn't even bother to mention what symbol this does matter for. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
[PATCH] sparc64: Add preprocessor symbols for PAGE_* pgprot_t values.
Kernel code assumes that the PAGE_* values are preprocessor symbols, and that therefore arch support can be checked for with #ifdef. At the moment, sparc64 does not implement any of the symbols checked for, so these checks happen to work. To prevent potential breakage when another #ifdef check is added or when sparc64 implements another PAGE_ value, make such #ifdef checks work by adding preprocessor symbols on top of the PAGE_* variables. Signed-off-by: Clemens Ladisch --- arch/sparc/include/asm/pgtable_64.h |4 1 file changed, 4 insertions(+) diff --git a/arch/sparc/include/asm/pgtable_64.h b/arch/sparc/include/asm/pgtable_64.h index bfeb626..a835fe9 100644 --- a/arch/sparc/include/asm/pgtable_64.h +++ b/arch/sparc/include/asm/pgtable_64.h @@ -216,9 +216,13 @@ pte_t mk_pte_io(unsigned long, pgprot_t, int, unsigned long); unsigned long pte_sz_bits(unsigned long size); extern pgprot_t PAGE_KERNEL; +#define PAGE_KERNELPAGE_KERNEL extern pgprot_t PAGE_KERNEL_LOCKED; +#define PAGE_KERNEL_LOCKED PAGE_KERNEL_LOCKED extern pgprot_t PAGE_COPY; +#define PAGE_COPY PAGE_COPY extern pgprot_t PAGE_SHARED; +#define PAGE_SHAREDPAGE_SHARED /* XXX This uglyness is for the atyfb driver's sparc mmap() support. XXX */ extern unsigned long _PAGE_IE; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/