sched, s390: Fix the fallout of increasing the offset of 'thread_struct' within 'task_struct'

[Ingo Molnar]

* Guenter <li...@roeck-us.net> 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 <mi...@kernel.org>

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 = &current->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;
+
        switch (vic) {
        case 1: /* invalid vector operation */
                si_code = FPE_FLTINV;
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/