Jordan Niethe's on March 20, 2020 3:17 pm: > 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. > > Signed-off-by: Jordan Niethe <jniet...@gmail.com>
Reviewed-by: Nicholas Piggin <npig...@gmail.com> > --- > v4: New to series > --- > arch/powerpc/kernel/vmlinux.lds.S | 2 +- > arch/powerpc/xmon/xmon.c | 22 +++++++++++++--------- > 2 files changed, 14 insertions(+), 10 deletions(-) > > diff --git a/arch/powerpc/kernel/vmlinux.lds.S > b/arch/powerpc/kernel/vmlinux.lds.S > index b4c89a1acebb..e90845b8c300 100644 > --- a/arch/powerpc/kernel/vmlinux.lds.S > +++ b/arch/powerpc/kernel/vmlinux.lds.S > @@ -86,7 +86,7 @@ SECTIONS > ALIGN_FUNCTION(); > #endif > /* careful! __ftr_alt_* sections need to be close to .text */ > - *(.text.hot TEXT_MAIN .text.fixup .text.unlikely .fixup > __ftr_alt_* .ref.text); > + *(.text.hot TEXT_MAIN .text.fixup .text.unlikely .fixup > __ftr_alt_* .ref.text .text.xmon_bpts); > #ifdef CONFIG_PPC64 > *(.tramp.ftrace.text); > #endif > diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c > index 02e3bd62cab4..7875d1a37770 100644 > --- a/arch/powerpc/xmon/xmon.c > +++ b/arch/powerpc/xmon/xmon.c > @@ -97,7 +97,7 @@ 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; > @@ -109,6 +109,7 @@ struct bpt { > #define BP_DABR 4 > > #define NBPTS 256 > +#define BPT_WORDS 2 > static struct bpt bpts[NBPTS]; > static struct bpt dabr; > static struct bpt *iabr; > @@ -116,6 +117,8 @@ static unsigned bpinstr = 0x7fe00008; /* trap */ > > #define BP_NUM(bp) ((bp) - bpts + 1) > > +static unsigned int __section(.text.xmon_bpts) bpt_table[NBPTS * BPT_WORDS]; > + > /* Prototypes */ > static int cmds(struct pt_regs *); > static int mread(unsigned long, void *, int); > @@ -852,16 +855,16 @@ static struct bpt *at_breakpoint(unsigned long pc) > static struct bpt *in_breakpoint_table(unsigned long nip, unsigned long > *offp) > { > unsigned long off; > + unsigned long bp_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])) > + bp_off = off % (sizeof(unsigned int) * BPT_WORDS); > + if (bp_off != 0 && bp_off != 4) > return NULL; > - *offp = off - offsetof(struct bpt, instr[0]); > - return (struct bpt *) (nip - off); > + *offp = bp_off; > + return bpts + ((off - bp_off) / (sizeof(unsigned int) * BPT_WORDS)); > } > > static struct bpt *new_breakpoint(unsigned long a) > @@ -876,7 +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; > } > } > -- > 2.17.1 > >