Anyone have any thoughts or comments on this?
On 19/01/16 15:56, 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. > > Using conventional stack parameters passed to these functions means the > code here does not need to know the exact details of how the underlying > entry handler layed these structs out on the stack. > > 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 aliasing of the regs and switch stack pointers, caused by their > construction from pointers derived from the dummy long function parameter, > is resulting in the gcc optimizer removing what it thinks is useless > updates to the regs fields. Large parts of restore_sigcontext() and > mangle_kernel_stack() functions get optimized out. 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. > > 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. > > 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 <[email protected]> > --- > 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 > jbsr do_sigreturn > + addql #8,%sp > 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 > jbsr do_rt_sigreturn > + addql #8,%sp > 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) > { > - struct switch_stack *sw = (struct switch_stack *) &__unused; > - struct pt_regs *regs = (struct pt_regs *) (sw + 1); > 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) > { > - struct switch_stack *sw = (struct switch_stack *) &__unused; > - struct pt_regs *regs = (struct pt_regs *) (sw + 1); > unsigned long usp = rdusp(); > struct rt_sigframe __user *frame = (struct rt_sigframe __user *)(usp - > 4); > sigset_t set; > -- To unsubscribe from this list: send the line "unsubscribe linux-m68k" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
