linux/arch/sparc/prom/cif.S
David S. Miller ef3e035c3a sparc64: Fix register corruption in top-most kernel stack frame during boot.
Meelis Roos reported that kernels built with gcc-4.9 do not boot, we
eventually narrowed this down to only impacting machines using
UltraSPARC-III and derivitive cpus.

The crash happens right when the first user process is spawned:

[   54.451346] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000004
[   54.451346]
[   54.571516] CPU: 1 PID: 1 Comm: init Not tainted 3.16.0-rc2-00211-gd7933ab #96
[   54.666431] Call Trace:
[   54.698453]  [0000000000762f8c] panic+0xb0/0x224
[   54.759071]  [000000000045cf68] do_exit+0x948/0x960
[   54.823123]  [000000000042cbc0] fault_in_user_windows+0xe0/0x100
[   54.902036]  [0000000000404ad0] __handle_user_windows+0x0/0x10
[   54.978662] Press Stop-A (L1-A) to return to the boot prom
[   55.050713] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000004

Further investigation showed that compiling only per_cpu_patch() with
an older compiler fixes the boot.

Detailed analysis showed that the function is not being miscompiled by
gcc-4.9, but it is using a different register allocation ordering.

With the gcc-4.9 compiled function, something during the code patching
causes some of the %i* input registers to get corrupted.  Perhaps
we have a TLB miss path into the firmware that is deep enough to
cause a register window spill and subsequent restore when we get
back from the TLB miss trap.

Let's plug this up by doing two things:

1) Stop using the firmware stack for client interface calls into
   the firmware.  Just use the kernel's stack.

2) As soon as we can, call into a new function "start_early_boot()"
   to put a one-register-window buffer between the firmware's
   deepest stack frame and the top-most initial kernel one.

Reported-by: Meelis Roos <mroos@linux.ee>
Tested-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: David S. Miller <davem@davemloft.net>
2014-10-24 09:52:49 -07:00

48 lines
947 B
ArmAsm

/* cif.S: PROM entry/exit assembler trampolines.
*
* Copyright (C) 1996, 1997 Jakub Jelinek (jj@sunsite.mff.cuni.cz)
* Copyright (C) 2005, 2006 David S. Miller <davem@davemloft.net>
*/
#include <asm/pstate.h>
#include <asm/cpudata.h>
#include <asm/thread_info.h>
.text
.globl prom_cif_direct
prom_cif_direct:
save %sp, -192, %sp
sethi %hi(p1275buf), %o1
or %o1, %lo(p1275buf), %o1
ldx [%o1 + 0x0008], %l2 ! prom_cif_handler
mov %g4, %l0
mov %g5, %l1
mov %g6, %l3
call %l2
mov %i0, %o0 ! prom_args
mov %l0, %g4
mov %l1, %g5
mov %l3, %g6
ret
restore
.globl prom_cif_callback
prom_cif_callback:
sethi %hi(p1275buf), %o1
or %o1, %lo(p1275buf), %o1
save %sp, -192, %sp
TRAP_LOAD_THREAD_REG(%g6, %g1)
LOAD_PER_CPU_BASE(%g5, %g6, %g4, %g3, %o0)
ldx [%g6 + TI_TASK], %g4
call prom_world
mov 0, %o0
ldx [%i1 + 0x000], %l2
call %l2
mov %i0, %o0
mov %o0, %l1
call prom_world
mov 1, %o0
ret
restore %l1, 0, %o0