Subject: Re: [PATCH v7 18/28] powerpc/xmon: Use a function for reading instructions

From: Alistair Popple <[email-masked]>
Date: Tue, 05 May 2020 12:07:36 +1000

Shouldn't change anything and will be correct once prefix instructions are 
defined.

Reviewed-by: Alistair Popple <[email-masked]>

On Friday, 1 May 2020 1:42:10 PM AEST 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 <[email-masked]>
> ---
> v5: New to series, seperated from "Add prefixed instructions to
>     instruction data type"
> v6: mread_instr(): correctly return error status
> ---
>  arch/powerpc/xmon/xmon.c | 28 ++++++++++++++++++++++++----
>  1 file changed, 24 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> index cde733a82366..1947821e425d 100644
> --- a/arch/powerpc/xmon/xmon.c
> +++ b/arch/powerpc/xmon/xmon.c
> @@ -122,6 +122,7 @@ static unsigned bpinstr = 0x7fe00008;	/* trap */
>  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);
> @@ -896,7 +897,7 @@ 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)) {
>  			printf("Couldn't read instruction at %lx, "
>  			       "disabling breakpoint there\n", bp->address);
>  			bp->enabled = 0;
> @@ -946,7 +947,7 @@ 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)
> @@ -1162,7 +1163,7 @@ 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",
> @@ -1329,7 +1330,7 @@ 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;
>  	}
> @@ -2122,6 +2123,25 @@ mwrite(unsigned long adrs, void *buf, int size)
>  	return n;
>  }
> 
> +static int
> +mread_instr(unsigned long adrs, struct ppc_inst *instr)
> +{
> +	volatile int n;
> +
> +	n = 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);
> +		n = ppc_inst_len(*instr);
> +	}
> +	catch_memory_errors = 0;
> +	return n;
> +}
> +
>  static int fault_type;
>  static int fault_except;
>  static char *fault_chars[] = { "--", "**", "##" };