Hi Greg, 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 <[email protected]> > --- > 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; Philippe -- Philippe De Muyter +32 2 6101532 Macq SA rue de l'Aeronef 2 B-1140 Bruxelles -- 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
