On 07/20/2015 12:34 AM, Ingo Molnar wrote:
* Guenter <[email protected]> wrote:Hi, Commit 0c8c0f03e3a2 ("x86/fpu, sched: Dynamically allocate 'struct fpu'") causes s390 builds in mainline to fail as follows. arch/s390/kernel/traps.c: Assembler messages: arch/s390/kernel/traps.c:262: Error: operand out of range (0x00000000000023e8 is not between 0x0000000000000000 and 0x0000000000000fff) arch/s390/kernel/traps.c:300: Error: operand out of range (0x00000000000023e8 is not between 0x0000000000000000 and 0x0000000000000fff)Yeah, so I'm really out on a limb here as I know next to nothing about s390 assembly, but the build failure appears to be analogous to the arm64 one: the offset of thread_struct fields within task_struct increased due to commit 0c8c0f03e3a2 ("x86/fpu, sched: Dynamically allocate 'struct fpu'"), which increased assembly offsets beyond the limit this instruction can apparently encode. Does the (untested!) patch below help? It's an equivalent transformation on the C side, but it might cause GCC to generate different assembly code, because we now have a temporary variable with much smaller offsets. The code is also a tiny bit cleaner this way, as the 'current->thread.fp_regs' pattern isn't repeated twice. In case this works: Signed-off-by: Ingo Molnar <[email protected]> Thanks, Ingo ================> arch/s390/kernel/traps.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/arch/s390/kernel/traps.c b/arch/s390/kernel/traps.c index 4d96c9f53455..db6f0eec55b5 100644 --- a/arch/s390/kernel/traps.c +++ b/arch/s390/kernel/traps.c @@ -251,6 +251,7 @@ int alloc_vector_registers(struct task_struct *tsk) void vector_exception(struct pt_regs *regs) { + s390_fp_regs *fp_regs = ¤t->thread.fp_regs; int si_code, vic; if (!MACHINE_HAS_VX) { @@ -259,8 +260,9 @@ void vector_exception(struct pt_regs *regs) } /* get vector interrupt code from fpc */ - asm volatile("stfpc %0" : "=m" (current->thread.fp_regs.fpc)); - vic = (current->thread.fp_regs.fpc & 0xf00) >> 8; + asm volatile("stfpc %0" : "=m" (fp_regs->fpc)); + vic = (fp_regs->fpc & 0xf00) >> 8; +
No idea why, but this still fails with the same error (I suspect the compiler tries to optimize the fp_regs variable away). I can compile the code by using a local variable '__u32 fpc', but obviously I don't know if that is correct. I don't have a working qemu configuration for s390, so I can not run any tests. Guenter -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
