On Friday, 1 May 2020 1:41:54 PM AEST Jordan Niethe wrote: > To execute an instruction out of line after a breakpoint, the NIP is set > to the address of struct bpt::instr. Here a copy of the instruction that > was replaced with a breakpoint is kept, along with a trap so normal flow > can be resumed after XOLing. The struct bpt's are located within the > data section. This is problematic as the data section may be marked as > no execute. > > Instead of each struct bpt holding the instructions to be XOL'd, make a > new array, bpt_table[], with enough space to hold instructions for the > number of supported breakpoints. A later patch will move this to the > text section. > Make struct bpt::instr a pointer to the instructions in bpt_table[] > associated with that breakpoint. This association is a simple mapping: > bpts[n] -> bpt_table[n * words per breakpoint]. Currently we only need > the copied instruction followed by a trap, so 2 words per breakpoint. > > Signed-off-by: Jordan Niethe <jniet...@gmail.com> > --- > v4: New to series > v5: - Do not use __section(), use a .space directive in .S file > - Simplify in_breakpoint_table() calculation > - Define BPT_SIZE > v6: - Seperate moving to text section > --- > arch/powerpc/xmon/xmon.c | 21 ++++++++++++--------- > 1 file changed, 12 insertions(+), 9 deletions(-) > > diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c > index f91ae2c9adbe..6ba7f66c1dd0 100644 > --- a/arch/powerpc/xmon/xmon.c > +++ b/arch/powerpc/xmon/xmon.c > @@ -98,7 +98,7 @@ static long *xmon_fault_jmp[NR_CPUS]; > /* Breakpoint stuff */ > struct bpt { > unsigned long address; > - unsigned int instr[2]; > + unsigned int *instr; > atomic_t ref_count; > int enabled; > unsigned long pad; > @@ -117,6 +117,10 @@ static unsigned bpinstr = 0x7fe00008; /* trap */ > > #define BP_NUM(bp) ((bp) - bpts + 1) > > +#define BPT_SIZE (sizeof(unsigned int) * 2) > +#define BPT_WORDS (BPT_SIZE / sizeof(unsigned int))
Minor nit-pick but IMHO this would be more logical if you defined BPT_WORDS first like so: #define BPT_WORDS (2) #define BPT_SIZE (sizeof(unsigned int) * BPT_WORDS) Otherwise this looks good and I think the offset calculations below are correct so: Reviewed-by: Alistair Popple <alist...@popple.id.au> > +static unsigned int bpt_table[NBPTS * BPT_WORDS]; > + > /* Prototypes */ > static int cmds(struct pt_regs *); > static int mread(unsigned long, void *, int); > @@ -854,15 +858,13 @@ static struct bpt *in_breakpoint_table(unsigned long > nip, unsigned long *offp) { > unsigned long off; > > - off = nip - (unsigned long) bpts; > - if (off >= sizeof(bpts)) > + off = nip - (unsigned long) bpt_table; > + if (off >= sizeof(bpt_table)) > return NULL; > - off %= sizeof(struct bpt); > - if (off != offsetof(struct bpt, instr[0]) > - && off != offsetof(struct bpt, instr[1])) > + *offp = off % BPT_SIZE; > + if (*offp != 0 && *offp != 4) > return NULL; > - *offp = off - offsetof(struct bpt, instr[0]); > - return (struct bpt *) (nip - off); > + return bpts + (off / BPT_SIZE); > } > > static struct bpt *new_breakpoint(unsigned long a) > @@ -877,7 +879,8 @@ static struct bpt *new_breakpoint(unsigned long a) > for (bp = bpts; bp < &bpts[NBPTS]; ++bp) { > if (!bp->enabled && atomic_read(&bp->ref_count) == 0) { > bp->address = a; > - patch_instruction(&bp->instr[1], bpinstr); > + bp->instr = bpt_table + ((bp - bpts) * BPT_WORDS); > + patch_instruction(bp->instr + 1, bpinstr); > return bp; > } > }