Messages in this thread | | | Date | Mon, 17 Jun 2019 17:13:30 +0100 | From | Will Deacon <> | Subject | Re: [PATCH] arm64/sve: fix genksyms generation |
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On Mon, Jun 17, 2019 at 02:21:46PM +0200, Arnd Bergmann wrote: > On Mon, Jun 17, 2019 at 1:26 PM Will Deacon <will.deacon@arm.com> wrote: > > 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.
Hmm, I've failed to reproduce the issue with that config and either GCC (7.1.1 and 8.3.0) or Clang (a flavour of 9.0.0 from a few months ago).
> > > 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.
Ok, but the patch that appears to cause this problem doesn't change the type of anything we're exporting. The symbol in your log is "kernel_neon_begin" which is:
void kernel_neon_begin(void);
so I'm still fairly confused about the problem. In fact, even if I create a silly:
void will_kernel_neon_begin(__uint128_t);
function, then somehow I see it being processed:
__crc_will_kernel_neon_begin = 0x5401d250;
Is there some way that your passing '-w' to genksyms?
Will
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