On Fri, Mar 14, 2025 at 01:05:15PM +0100, Arnd Bergmann wrote: > On Fri, Mar 14, 2025, at 12:55, Will Deacon wrote: > > On Fri, Mar 14, 2025 at 08:09:39AM +0100, Thomas Huth wrote: > >> __ASSEMBLY__ is only defined by the Makefile of the kernel, so > >> this is not really useful for uapi headers (unless the userspace > >> Makefile defines it, too). Let's switch to __ASSEMBLER__ which > >> gets set automatically by the compiler when compiling assembly > >> code. > >> > >> Cc: Catalin Marinas <catalin.marinas@xxxxxxx> > >> Cc: Will Deacon <will@xxxxxxxxxx> > >> Signed-off-by: Thomas Huth <thuth@xxxxxxxxxx> > >> --- > >> arch/arm64/include/uapi/asm/kvm.h | 2 +- > >> arch/arm64/include/uapi/asm/ptrace.h | 4 ++-- > >> arch/arm64/include/uapi/asm/sigcontext.h | 4 ++-- > >> 3 files changed, 5 insertions(+), 5 deletions(-) > > > > Is there a risk of breaking userspace with this? I wonder if it would > > be more conservative to do something like: > > > > #if !defined(__ASSEMBLY__) && !defined(__ASSEMBLER__) > > > > so that if somebody is doing '#define __ASSEMBLY__' then they get the > > same behaviour as today. > > > > Or maybe we don't care? > > I think the main risk we would have is user applications relying > on the __ASSEMBLER__ checks in new kernel headers and not defining > __ASSEMBLY__. This would result in the application not building > against old kernel headers that only check against __ASSEMBLY__. Hmm. I hadn't thought about the case of old headers :/ A quick Debian codesearch shows that glibc might #define __ASSEMBLY__ for some arch-specific headers: https://codesearch.debian.net/search?q=%23define+__ASSEMBLY__&literal=1 which is what I was more worried about. > Checking for both in the kernel headers does not solve this > problem, and I think we can still decide that we don't care: > in the worst case, an application using the headers from assembly > will have to get fixed later when it needs to be built against > old headers. Old headers might also just be missing definitions that the application wants, so I suppose there's always the potential for some manual effort in that case. Will
