powerpc/xmon: Move breakpoint instructions to own array (51c9ba11) · Commits · 戴 / test

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 <jniethe5@gmail.com> Signed-off-by:

Michael Ellerman <mpe@ellerman.id.au> Reviewed-by:

Alistair Popple <alistair@popple.id.au> Link: https://lore.kernel.org/r/20200506034050.24806-3-jniethe5@gmail.com

arch/powerpc/xmon/xmon.c

+12 −9

Original line number	Diff line number	Diff line
		@@ -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))
		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;
		}
		}

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