Messages in this thread | | | From | Arnd Bergmann <> | Date | Mon, 17 Jun 2019 14:21:46 +0200 | Subject | Re: [PATCH] arm64/sve: fix genksyms generation |
| |
On Mon, Jun 17, 2019 at 1:26 PM Will Deacon <will.deacon@arm.com> wrote: > > Hi Arnd, > > On Mon, Jun 17, 2019 at 12:42:11PM +0200, Arnd Bergmann wrote: > > genksyms does not understand __uint128_t, so we get a build failure > > in the fpsimd module when it cannot export a symbol right: > > The fpsimd code is builtin, so which module is actually failing? My > allmodconfig build succeeds, so I must be missing something.
It happened for me on randconfig builds, you can find one such configuration at https://pastebin.com/cU8iQ4ta now. I was building this with clang rather than gcc, which may affect the issue, but I assumed not.
> > WARNING: EXPORT symbol "kernel_neon_begin" [vmlinux] version generation failed, symbol will not be versioned. > > /home/arnd/cross/x86_64/gcc-8.1.0-nolibc/aarch64-linux/bin/aarch64-linux-ld: arch/arm64/kernel/fpsimd.o: relocation R_AARCH64_ABS32 against `__crc_kernel_neon_begin' can not be used when making a shared object > > arch/arm64/kernel/fpsimd.o:(.data+0x0): dangerous relocation: unsupported relocation > > arch/arm64/kernel/fpsimd.o:(".discard.addressable"+0x0): dangerous relocation: unsupported relocation > > arch/arm64/kernel/fpsimd.o:(".discard.addressable"+0x8): dangerous relocation: unsupported relocation > > > > We could teach genksyms about the type, but it's easier to just > > work around it by defining that type locally in a way that genksyms > > understands. > > > > Fixes: 41040cf7c5f0 ("arm64/sve: Fix missing SVE/FPSIMD endianness conversions") > > I can't see which part of that patch causes the problem, so I'm a bit wary > of the fix. We've been using __uint128_t for a while now, and I see there's > one in the x86 kvm code as well, so it would be nice to understand what's > happening here so that we can avoid running into it in future as well.
The problem is only in files that export a symbol. This is also the case in arch/x86/kernel/kvm.c, but it may be lucky because the type only appears /after/ the last export in that file.
> > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > > --- > > arch/arm64/kernel/fpsimd.c | 3 +++ > > 1 file changed, 3 insertions(+) > > > > diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c > > index 07f238ef47ae..2aba07cccf50 100644 > > --- a/arch/arm64/kernel/fpsimd.c > > +++ b/arch/arm64/kernel/fpsimd.c > > @@ -400,6 +400,9 @@ static int __init sve_sysctl_init(void) { return 0; } > > #define ZREG(sve_state, vq, n) ((char *)(sve_state) + \ > > (SVE_SIG_ZREG_OFFSET(vq, n) - SVE_SIG_REGS_OFFSET)) > > > > +#ifdef __GENKSYMS__ > > +typedef __u64 __uint128_t[2]; > > +#endif > > I suspect I need to figure out what genksyms is doing, but I'm nervous > about exposing this as an array type without understanding whether or > not that has consequences for its operation.
The entire point is genksyms is to ensure that types of exported symbols are compatible. To do this, it has a limited parser for C source code that understands the basic types (char, int, long, _Bool, etc) and how to aggregate them into structs and function arguments. This process has always been fragile, and it clearly breaks when it fails to understand a particular type.
Arnd
| |