Re: [PATCH v5 13/21] powerpc/xmon: Use a function for reading instructions

[Balamuruhan S <bala24@linux.ibm.com>]

On Wed, 2020-04-08 at 12:18 +1000, Jordan Niethe wrote:
> On Tue, Apr 7, 2020 at 9:31 PM Balamuruhan S <bala24@linux.ibm.com> wrote:
> > On Mon, 2020-04-06 at 18:09 +1000, Jordan Niethe wrote:
> > > Currently in xmon, mread() is used for reading instructions. In
> > > preparation for prefixed instructions, create and use a new function,
> > > mread_instr(), especially for reading instructions.
> > > 
> > > Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
> > > ---
> > > v5: New to series, seperated from "Add prefixed instructions to
> > > instruction data type"
> > > ---
> > >  arch/powerpc/xmon/xmon.c | 24 ++++++++++++++++++++----
> > >  1 file changed, 20 insertions(+), 4 deletions(-)
> > > 
> > > diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> > > index 5e3949322a6c..6f4cf01a58c1 100644
> > > --- a/arch/powerpc/xmon/xmon.c
> > > +++ b/arch/powerpc/xmon/xmon.c
> > > @@ -125,6 +125,7 @@ extern unsigned int bpt_table[NBPTS * BPT_WORDS];
> > >  static int cmds(struct pt_regs *);
> > >  static int mread(unsigned long, void *, int);
> > >  static int mwrite(unsigned long, void *, int);
> > > +static int mread_instr(unsigned long, struct ppc_inst *);
> > >  static int handle_fault(struct pt_regs *);
> > >  static void byterev(unsigned char *, int);
> > >  static void memex(void);
> > > @@ -899,7 +900,7 @@ static void insert_bpts(void)
> > >       for (i = 0; i < NBPTS; ++i, ++bp) {
> > >               if ((bp->enabled & (BP_TRAP|BP_CIABR)) == 0)
> > >                       continue;
> > > -             if (mread(bp->address, &instr, 4) != 4) {
> > > +             if (!mread_instr(bp->address, &instr)) {
> > 
> > Are these checks made based on whether `ppc_inst_len()` returns bool from
> > mread_instr() ?
> No, it was meant to be the length itself returned with a length of 0
> indicating an error. I will need to fix that.


I doubt it would return 0, whether we read instruction or not ppc_inst_len()
would always return sizeof(struct ppc_inst).

can we do something like,

static int
mread_instr(unsigned long adrs, struct ppc_inst *instr)
{
	int size = 0;
	if (setjmp(bus_error_jmp) == 0) {
		catch_memory_errors = 1;
		sync();
		*instr = ppc_inst_read((struct ppc_inst *)adrs);
		sync();
		/* wait a little while to see if we get a machine check */
		__delay(200);
		size = ppc_inst_len(instr);
	}
	catch_memory_errors = 0;
	return size;
}

-- Bala
> > -- Bala
> > 
> > 
> > >                       printf("Couldn't read instruction at %lx, "
> > >                              "disabling breakpoint there\n", bp-
> > > >address);
> > >                       bp->enabled = 0;
> > > @@ -949,7 +950,7 @@ static void remove_bpts(void)
> > >       for (i = 0; i < NBPTS; ++i, ++bp) {
> > >               if ((bp->enabled & (BP_TRAP|BP_CIABR)) != BP_TRAP)
> > >                       continue;
> > > -             if (mread(bp->address, &instr, 4) == 4
> > > +             if (mread_instr(bp->address, &instr)
> > >                   && ppc_inst_equal(instr, ppc_inst(bpinstr))
> > >                   && patch_instruction(
> > >                       (struct ppc_inst *)bp->address, ppc_inst_read(bp-
> > > > instr)) != 0)
> > > @@ -1165,7 +1166,7 @@ static int do_step(struct pt_regs *regs)
> > >       force_enable_xmon();
> > >       /* check we are in 64-bit kernel mode, translation enabled */
> > >       if ((regs->msr & (MSR_64BIT|MSR_PR|MSR_IR)) == (MSR_64BIT|MSR_IR))
> > > {
> > > -             if (mread(regs->nip, &instr, 4) == 4) {
> > > +             if (mread_instr(regs->nip, &instr)) {
> > >                       stepped = emulate_step(regs, instr);
> > >                       if (stepped < 0) {
> > >                               printf("Couldn't single-step %s
> > > instruction\n",
> > > @@ -1332,7 +1333,7 @@ static long check_bp_loc(unsigned long addr)
> > >               printf("Breakpoints may only be placed at kernel
> > > addresses\n");
> > >               return 0;
> > >       }
> > > -     if (!mread(addr, &instr, sizeof(instr))) {
> > > +     if (!mread_instr(addr, &instr)) {
> > >               printf("Can't read instruction at address %lx\n", addr);
> > >               return 0;
> > >       }
> > > @@ -2125,6 +2126,21 @@ mwrite(unsigned long adrs, void *buf, int size)
> > >       return n;
> > >  }
> > > 
> > > +static int
> > > +mread_instr(unsigned long adrs, struct ppc_inst *instr)
> > > +{
> > > +     if (setjmp(bus_error_jmp) == 0) {
> > > +             catch_memory_errors = 1;
> > > +             sync();
> > > +             *instr = ppc_inst_read((struct ppc_inst *)adrs);
> > > +             sync();
> > > +             /* wait a little while to see if we get a machine check */
> > > +             __delay(200);
> > > +     }
> > > +     catch_memory_errors = 0;
> > > +     return ppc_inst_len(*instr);
> > > +}
> > > +
> > >  static int fault_type;
> > >  static int fault_except;
> > >  static char *fault_chars[] = { "--", "**", "##" };