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Subject[PATCH] sched, s390: Fix the fallout of increasing the offset of 'thread_struct' within 'task_struct'

* Heiko Carstens <heiko.carstens@de.ibm.com> wrote:

> > I've tested it on a number of x86 platforms, and I cross-built it to a handful
> > of architectures:
> >
> > (warns) (warns)
> > testing x86-64: -git: pass ( 0), -tip: pass ( 0)
> > testing x86-32: -git: pass ( 0), -tip: pass ( 0)
> > testing arm: -git: pass ( 1359), -tip: pass ( 1359)
> > testing cris: -git: pass ( 1031), -tip: pass ( 1031)
> > testing m32r: -git: pass ( 1135), -tip: pass ( 1135)
> > testing m68k: -git: pass ( 1471), -tip: pass ( 1471)
> > testing mips: -git: pass ( 1162), -tip: pass ( 1162)
> > testing mn10300: -git: pass ( 1058), -tip: pass ( 1058)
> > testing parisc: -git: pass ( 1846), -tip: pass ( 1846)
> > testing sparc: -git: pass ( 1185), -tip: pass ( 1185)
> >
> > ... so I hope the cross-arch impact 'none', as intended.
> >
> > (by Dave Hansen)
>
> Unfortunately not true. It breaks the build on s390 since a couple of
> displacements used in asm code now get too large:
>
> arch/s390/kernel/entry.S:181: Error: operand out of range (0x00000000000018a8 is not between 0x0000000000000000 and 0x0000000000000fff)
> arch/s390/kernel/entry.S:191: Error: operand out of range (0x00000000000018a8 is not between 0x0000000000000000 and 0x0000000000000fff)
> arch/s390/kernel/entry.S:423: Error: operand out of range (0x0000000000001924 is not between 0x0000000000000000 and 0x0000000000000fff)
> arch/s390/kernel/entry.S:437: Error: operand out of range (0x00000000000018e8 is not between 0x0000000000000000 and 0x0000000000000fff)
> arch/s390/kernel/entry.S:438: Error: operand out of range (0x00000000000018e0 is not between 0x0000000000000000 and 0x0000000000000fff)
> arch/s390/kernel/entry.S:439: Error: operand out of range (0x00000000000018f0 is not between 0x0000000000000000 and 0x0000000000000fff)
> make[1]: *** [arch/s390/kernel/entry.o] Error 1
>
> Let's see how we can fix this.

There's also a traps.c build breakage reported below - and an RFC fix for it.

Thanks,

Ingo

=========================>

* Guenter <linux@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 <mingo@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;

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