On Tue, 14 Feb 2006, Dale Farnsworth wrote: > From: Dale Farnsworth <dale at farnsworth.org> > > On PPC Book E processsors, we currently handle debug > exceptions on the critical exception stack (debug stack > for E200). This causes problems with the kgdb single > step handler, which calls smp_processor_id() and spin_lock(), > which reference current_thread_info(), which only works when > we are on the kernel stack. > > We address this by switching to the kernel stack early while > handling debug exceptions. Note that the entry values of r10 > and r11 are still saved on the critical exception (or debug) stack. > > Signed-off-by: Dale Farnsworth <dale at farnsworth.org> >
Paul, We were wondering if you or David remember why a specific critical exception stack was added in the 40x port from 2.4 to 2.6? - kumar > --- > > This is low level code and needs careful review. > I've only tested it on mpc8548cds. > > I didn't find the corresponding code in arch/powerpc, > so I assume Book E support hasn't been merged yet. > > arch/ppc/kernel/head_booke.h | 15 +++++++++------ > 1 file changed, 9 insertions(+), 6 deletions(-) > > diff --git a/arch/ppc/kernel/head_booke.h b/arch/ppc/kernel/head_booke.h > index f3d274c..a5eec51 100644 > --- a/arch/ppc/kernel/head_booke.h > +++ b/arch/ppc/kernel/head_booke.h > @@ -92,7 +92,8 @@ > * registers as the normal prolog above. Instead we use a portion of the > * critical/machine check exception stack at low physical addresses. > */ > -#define EXC_LEVEL_EXCEPTION_PROLOG(exc_level, exc_level_srr0, > exc_level_srr1) \ > +#define EXC_LEVEL_EXCEPTION_PROLOG(exc_level, exc_level_srr0, > \ > + exc_level_srr1, kernel_sp_reg) \ > mtspr exc_level##_SPRG,r8; \ > BOOKE_LOAD_EXC_LEVEL_STACK(exc_level);/* r8 points to the exc_level > stack*/ \ > stw r10,GPR10-INT_FRAME_SIZE(r8); \ > @@ -100,7 +101,7 @@ > mfcr r10; /* save CR in r10 for now */\ > mfspr r11,exc_level_srr1; /* check whether user or kernel */\ > andi. r11,r11,MSR_PR; \ > - mr r11,r8; \ > + mr r11,kernel_sp_reg; \ > mfspr r8,exc_level##_SPRG; \ > beq 1f; \ > /* COMING FROM USER MODE */ \ > @@ -128,11 +129,13 @@ > SAVE_2GPRS(7, r11) > > #define CRITICAL_EXCEPTION_PROLOG \ > - EXC_LEVEL_EXCEPTION_PROLOG(CRIT, SPRN_CSRR0, SPRN_CSRR1) > + EXC_LEVEL_EXCEPTION_PROLOG(CRIT, SPRN_CSRR0, SPRN_CSRR1, r8) > +#define CRITICAL_EXCEPTION_ON_KERNEL_STACK_PROLOG \ > + EXC_LEVEL_EXCEPTION_PROLOG(CRIT, SPRN_CSRR0, SPRN_CSRR1, r1) > #define DEBUG_EXCEPTION_PROLOG \ > - EXC_LEVEL_EXCEPTION_PROLOG(DEBUG, SPRN_DSRR0, SPRN_DSRR1) > + EXC_LEVEL_EXCEPTION_PROLOG(DEBUG, SPRN_DSRR0, SPRN_DSRR1, r1) > #define MCHECK_EXCEPTION_PROLOG \ > - EXC_LEVEL_EXCEPTION_PROLOG(MCHECK, SPRN_MCSRR0, SPRN_MCSRR1) > + EXC_LEVEL_EXCEPTION_PROLOG(MCHECK, SPRN_MCSRR0, SPRN_MCSRR1, r8) > > /* > * Exception vectors. > @@ -268,7 +271,7 @@ label: > #else > #define DEBUG_EXCEPTION > \ > START_EXCEPTION(Debug); \ > - CRITICAL_EXCEPTION_PROLOG; \ > + CRITICAL_EXCEPTION_ON_KERNEL_STACK_PROLOG; \ > \ > /* \ > * If there is a single step or branch-taken exception in an \ >
