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linux-next/arch/sparc/prom/init_64.c
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

57 lines
1.3 KiB
C

/*
* init.c: Initialize internal variables used by the PROM
* library functions.
*
* Copyright (C) 1995 David S. Miller (davem@caip.rutgers.edu)
* Copyright (C) 1996,1997 Jakub Jelinek (jj@sunsite.mff.cuni.cz)
*/
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/string.h>
#include <linux/ctype.h>
#include <asm/openprom.h>
#include <asm/oplib.h>
/* OBP version string. */
char prom_version[80];
/* The root node of the prom device tree. */
int prom_stdout;
phandle prom_chosen_node;
/* You must call prom_init() before you attempt to use any of the
* routines in the prom library.
* It gets passed the pointer to the PROM vector.
*/
extern void prom_cif_init(void *);
void __init prom_init(void *cif_handler)
{
phandle node;
prom_cif_init(cif_handler);
prom_chosen_node = prom_finddevice(prom_chosen_path);
if (!prom_chosen_node || (s32)prom_chosen_node == -1)
prom_halt();
prom_stdout = prom_getint(prom_chosen_node, "stdout");
node = prom_finddevice("/openprom");
if (!node || (s32)node == -1)
prom_halt();
prom_getstring(node, "version", prom_version, sizeof(prom_version));
prom_printf("\n");
}
void __init prom_init_report(void)
{
printk("PROMLIB: Sun IEEE Boot Prom '%s'\n", prom_version);
printk("PROMLIB: Root node compatible: %s\n", prom_root_compatible);
}