On Sat, 10 Feb 2018, Tobias Jakobi wrote:

Hello,

I noticed a compile error with a recent version (4.4.115) of the 4.4.y branch: arch/x86/mm/kaiser.c: In function ‘kaiser_init’: arch/x86/mm/kaiser.c:348:8: error: ‘vsyscall_pgprot’ undeclared (first use in this function)

It seems like my combination of kernel options doesn't work for KAISER. X86_VSYSCALL_EMULATION is not set on my system, while LEGACY_VSYSCALL is set to NONE (LEGACY_VSYSCALL_NONE=y). I have managed to get things compiling again, by moving the 'extern unsigned long vsyscall_pgprot' outside of the preprocessor statement. This works for me, I guess because the code in question is never called during runtime anyway (vsyscall_enabled() always returns false).

With best wishes, Tobias

Yes, sorry about that, thanks Tobias. Same error on 4.9 too. Here's the patch that you correctly suggest, and it's good for both:

[PATCH 4.4 and 4.9] kaiser: fix compile error without vsyscall

Tobias noticed a compile error on 4.4.115, and it's the same on 4.9.80: arch/x86/mm/kaiser.c: In function ‘kaiser_init’: arch/x86/mm/kaiser.c:348:8: error: ‘vsyscall_pgprot’ undeclared (first use in this function)

It seems like his combination of kernel options doesn't work for KAISER. X86_VSYSCALL_EMULATION is not set on his system, while LEGACY_VSYSCALL is set to NONE (LEGACY_VSYSCALL_NONE=y). He managed to get things compiling again, by moving the 'extern unsigned long vsyscall_pgprot' outside of the preprocessor statement. This works because the optimizer removes that code (vsyscall_enabled() is always false) - and that's how it was done in some older backports.

Reported-by: Tobias Jakobi tjakobi@math.uni-bielefeld.de Signed-off-by: Hugh Dickins hughd@google.com ---

arch/x86/include/asm/vsyscall.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/include/asm/vsyscall.h +++ b/arch/x86/include/asm/vsyscall.h @@ -13,7 +13,6 @@ extern void map_vsyscall(void); */ extern bool emulate_vsyscall(struct pt_regs *regs, unsigned long address); extern bool vsyscall_enabled(void); -extern unsigned long vsyscall_pgprot; #else static inline void map_vsyscall(void) {} static inline bool emulate_vsyscall(struct pt_regs *regs, unsigned long address) @@ -22,5 +21,6 @@ static inline bool emulate_vsyscall(struct pt_regs *regs, unsigned long address) } static inline bool vsyscall_enabled(void) { return false; } #endif +extern unsigned long vsyscall_pgprot;

#endif /* _ASM_X86_VSYSCALL_H */