On Mon, 2020-04-06 at 18:09 +1000, 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. Place this array in 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.
we do 2 things here and we discussed to split it into 2 commits, may be
it is up to your thoughts and leave it to you. But otherwise rest looks
good to me.
-- Bala
>
> 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
> ---
> arch/powerpc/xmon/Makefile | 2 +-
> arch/powerpc/xmon/xmon.c | 23 +++++++++++++----------
> arch/powerpc/xmon/xmon_bpts.S | 8 ++++++++
> arch/powerpc/xmon/xmon_bpts.h | 8 ++++++++
> 4 files changed, 30 insertions(+), 11 deletions(-)
> create mode 100644 arch/powerpc/xmon/xmon_bpts.S
> create mode 100644 arch/powerpc/xmon/xmon_bpts.h
>
> diff --git a/arch/powerpc/xmon/Makefile b/arch/powerpc/xmon/Makefile
> index c3842dbeb1b7..515a13ea6f28 100644
> --- a/arch/powerpc/xmon/Makefile
> +++ b/arch/powerpc/xmon/Makefile
> @@ -21,7 +21,7 @@ endif
>
> ccflags-$(CONFIG_PPC64) := $(NO_MINIMAL_TOC)
>
> -obj-y += xmon.o nonstdio.o spr_access.o
> +obj-y += xmon.o nonstdio.o spr_access.o xmon_bpts.o
>
> ifdef CONFIG_XMON_DISASSEMBLY
> obj-y += ppc-dis.o ppc-opc.o
> diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> index 02e3bd62cab4..049375206510 100644
> --- a/arch/powerpc/xmon/xmon.c
> +++ b/arch/powerpc/xmon/xmon.c
> @@ -62,6 +62,7 @@
>
> #include "nonstdio.h"
> #include "dis-asm.h"
> +#include "xmon_bpts.h"
>
> #ifdef CONFIG_SMP
> static cpumask_t cpus_in_xmon = CPU_MASK_NONE;
> @@ -97,7 +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;
> @@ -108,7 +109,6 @@ struct bpt {
> #define BP_TRAP 2
> #define BP_DABR 4
>
> -#define NBPTS 256
> static struct bpt bpts[NBPTS];
> static struct bpt dabr;
> static struct bpt *iabr;
> @@ -116,6 +116,10 @@ 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))
> +extern unsigned int bpt_table[NBPTS * BPT_WORDS];
> +
> /* Prototypes */
> static int cmds(struct pt_regs *);
> static int mread(unsigned long, void *, int);
> @@ -853,15 +857,13 @@ 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)
> @@ -876,7 +878,8 @@ 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;
> }
> }
> diff --git a/arch/powerpc/xmon/xmon_bpts.S b/arch/powerpc/xmon/xmon_bpts.S
> new file mode 100644
> index 000000000000..ebb2dbc70ca8
> --- /dev/null
> +++ b/arch/powerpc/xmon/xmon_bpts.S
> @@ -0,0 +1,8 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#include <asm/ppc_asm.h>
> +#include <asm/asm-compat.h>
> +#include "xmon_bpts.h"
> +
> +.global bpt_table
> +bpt_table:
> + .space NBPTS * 8
> diff --git a/arch/powerpc/xmon/xmon_bpts.h b/arch/powerpc/xmon/xmon_bpts.h
> new file mode 100644
> index 000000000000..840e70be7945
> --- /dev/null
> +++ b/arch/powerpc/xmon/xmon_bpts.h
> @@ -0,0 +1,8 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef XMON_BPTS_H
> +#define XMON_BPTS_H
> +
> +#define NBPTS 256
> +
> +#endif /* XMON_BPTS_H */
> +
