On Mon, Feb 15, 2016 at 04:36:29PM +1000, Greg Ungerer wrote:
Create conventional stack parameters for the calls to do_sigreturn and
do_rt_sigreturn. The current C code for do_sigreturn and do_rt_sigreturn
dig into the stack to create local pointers to the saved switch stack
and the pt_regs structs.
The motivation for this change is a problem with non-MMU targets that
have broken signal return paths on newer versions of gcc. It appears as
though gcc has determined that the pointers into the saved stack structs,
and the saved structs themselves, are function parameters and updates to
them will be lost on function return, so they are optimized away. This
results in large parts of restore_sigcontext() and mangle_kernel_stack()
functions being removed. Of course this results in non-functional code
causing kernel oops. This problem has been observed with gcc version
5.2 and 5.3, and probably exists in earlier versions as well.
Using conventional stack parameter pointers passed to these functions has
the advantage of the code here not needing to know the exact details of
how the underlying entry handler layed these structs out on the stack.
So the rather ugly pointer setup casting and arg referencing can be
removed.
The resulting code after this change is a few bytes larger (due to the
overhead of creating the stack args and their tear down). Not being hot
paths I don't think this is too much of a problem here.
As an intermediate solution, I think that you can avoid part of that overhead ...
An alternative solution is to put a barrier() in the do_sigreturn() code,
but this doesn't feel quite as clean as this solution.
This change has been compile tested on all defconfigs, and run tested on
Atari (through aranym), ColdFire with MMU (M5407EVB) and ColdFire with
no-MMU (QEMU and M5208EVB).
Signed-off-by: Greg Ungerer <gerg@xxxxxxxxxxx>
---
v2: reworded the commit log message with better description of problem
arch/m68k/kernel/entry.S | 6 ++++++
arch/m68k/kernel/signal.c | 8 ++------
2 files changed, 8 insertions(+), 6 deletions(-)
diff --git a/arch/m68k/kernel/entry.S b/arch/m68k/kernel/entry.S
index b54ac7a..97cd3ea 100644
--- a/arch/m68k/kernel/entry.S
+++ b/arch/m68k/kernel/entry.S
@@ -71,13 +71,19 @@ ENTRY(__sys_vfork)
ENTRY(sys_sigreturn)
SAVE_SWITCH_STACK
+ movel %sp,%sp@- | switch_stack pointer
+ pea %sp@(SWITCH_STACK_SIZE+4) | pt_regs pointer
if you remove the above asm instruction ...
jbsr do_sigreturn
+ addql #8,%sp
change the 8 by 4 here ...
RESTORE_SWITCH_STACK
rts
ENTRY(sys_rt_sigreturn)
SAVE_SWITCH_STACK
+ movel %sp,%sp@- | switch_stack pointer
+ pea %sp@(SWITCH_STACK_SIZE+4) | pt_regs pointer
ditto here ...
jbsr do_rt_sigreturn
+ addql #8,%sp
and here ...
RESTORE_SWITCH_STACK
rts
diff --git a/arch/m68k/kernel/signal.c b/arch/m68k/kernel/signal.c
index af1c4f3..2dcee3a 100644
--- a/arch/m68k/kernel/signal.c
+++ b/arch/m68k/kernel/signal.c
@@ -737,10 +737,8 @@ badframe:
return 1;
}
-asmlinkage int do_sigreturn(unsigned long __unused)
+asmlinkage int do_sigreturn(struct pt_regs *regs, struct switch_stack *sw)
and if you use the following prototype :
asmlinkage int do_sigreturn(struct switch_stack *sw) ...
{
- struct switch_stack *sw = (struct switch_stack *) &__unused;
- struct pt_regs *regs = (struct pt_regs *) (sw + 1);
and keep the 'C' instruction above
unsigned long usp = rdusp();
struct sigframe __user *frame = (struct sigframe __user *)(usp - 4);
sigset_t set;
@@ -764,10 +762,8 @@ badframe:
return 0;
}
-asmlinkage int do_rt_sigreturn(unsigned long __unused)
+asmlinkage int do_rt_sigreturn(struct pt_regs *regs, struct switch_stack *sw)
same here
{
- struct switch_stack *sw = (struct switch_stack *) &__unused;
- struct pt_regs *regs = (struct pt_regs *) (sw + 1);
and here
unsigned long usp = rdusp();
struct rt_sigframe __user *frame = (struct rt_sigframe __user *)(usp - 4);
sigset_t set;
