[PATCH 05/18] powerpc sstep: Prepare to support prefixed instructions

Jordan Niethe jniethe5 at gmail.com
Fri Dec 20 16:11:35 AEDT 2019


On Wed, Dec 18, 2019 at 7:35 PM Daniel Axtens <dja at axtens.net> wrote:
>
> Jordan Niethe <jniethe5 at gmail.com> writes:
>
> > Currently all instructions are a single word long. A future ISA version
> > will include prefixed instructions which have a double word length. The
> > functions used for analysing and emulating instructions need to be
> > modified so that they can handle these new instruction types.
> >
> > A prefixed instruction is a word prefix followed by a word suffix. All
> > prefixes uniquely have the primary op-code 1. Suffixes may be valid word
> > instructions or instructions that only exist as suffixes.
> >
> > In handling prefixed instructions it will be convenient to treat the
> > suffix and prefix as separate words. To facilitate this modify
> > analyse_instr() and emulate_step() to take a take a suffix as a
> > parameter. For word instructions it does not matter what is passed in
> > here - it will be ignored.
> >
> > We also define a new flag, PREFIXED, to be used in instruction_op:type.
> > This flag will indicate when emulating an analysed instruction if the
> > NIP should be advanced by word length or double word length.
> >
> > The callers of analyse_instr() and emulate_step() will need their own
> > changes to be able to support prefixed instructions. For now modify them
> > to pass in 0 as a suffix.
> >
> > Note that at this point no prefixed instructions are emulated or
> > analysed - this is just making it possible to do so.
> >
> > Signed-off-by: Jordan Niethe <jniethe5 at gmail.com>
> > ---
> >  arch/powerpc/include/asm/ppc-opcode.h |  3 +++
> >  arch/powerpc/include/asm/sstep.h      |  8 +++++--
> >  arch/powerpc/include/asm/uaccess.h    | 30 +++++++++++++++++++++++++++
> >  arch/powerpc/kernel/align.c           |  2 +-
> >  arch/powerpc/kernel/hw_breakpoint.c   |  4 ++--
> >  arch/powerpc/kernel/kprobes.c         |  2 +-
> >  arch/powerpc/kernel/mce_power.c       |  2 +-
> >  arch/powerpc/kernel/optprobes.c       |  2 +-
> >  arch/powerpc/kernel/uprobes.c         |  2 +-
> >  arch/powerpc/kvm/emulate_loadstore.c  |  2 +-
> >  arch/powerpc/lib/sstep.c              | 12 ++++++-----
> >  arch/powerpc/lib/test_emulate_step.c  | 30 +++++++++++++--------------
> >  arch/powerpc/xmon/xmon.c              |  4 ++--
> >  13 files changed, 71 insertions(+), 32 deletions(-)
> >
> > diff --git a/arch/powerpc/include/asm/ppc-opcode.h b/arch/powerpc/include/asm/ppc-opcode.h
> > index c1df75edde44..a1dfa4bdd22f 100644
> > --- a/arch/powerpc/include/asm/ppc-opcode.h
> > +++ b/arch/powerpc/include/asm/ppc-opcode.h
> > @@ -377,6 +377,9 @@
> >  #define PPC_INST_VCMPEQUD            0x100000c7
> >  #define PPC_INST_VCMPEQUB            0x10000006
> >
> > +/* macro to check if a word is a prefix */
> > +#define IS_PREFIX(x) (((x) >> 26) == 1)
> > +
> >  /* macros to insert fields into opcodes */
> >  #define ___PPC_RA(a) (((a) & 0x1f) << 16)
> >  #define ___PPC_RB(b) (((b) & 0x1f) << 11)
> > diff --git a/arch/powerpc/include/asm/sstep.h b/arch/powerpc/include/asm/sstep.h
> > index 769f055509c9..6d4cb602e231 100644
> > --- a/arch/powerpc/include/asm/sstep.h
> > +++ b/arch/powerpc/include/asm/sstep.h
> > @@ -89,6 +89,9 @@ enum instruction_type {
> >  #define VSX_LDLEFT   4       /* load VSX register from left */
> >  #define VSX_CHECK_VEC        8       /* check MSR_VEC not MSR_VSX for reg >= 32 */
> >
> > +/* Prefixed flag, ORed in with type */
> > +#define PREFIXED     0x800
> > +
> >  /* Size field in type word */
> >  #define SIZE(n)              ((n) << 12)
> >  #define GETSIZE(w)   ((w) >> 12)
> > @@ -132,7 +135,7 @@ union vsx_reg {
> >   * otherwise.
> >   */
> >  extern int analyse_instr(struct instruction_op *op, const struct pt_regs *regs,
> > -                      unsigned int instr);
> > +                      unsigned int instr, unsigned int sufx);
> >
> >  /*
> >   * Emulate an instruction that can be executed just by updating
> > @@ -149,7 +152,8 @@ void emulate_update_regs(struct pt_regs *reg, struct instruction_op *op);
> >   * 0 if it could not be emulated, or -1 for an instruction that
> >   * should not be emulated (rfid, mtmsrd clearing MSR_RI, etc.).
> >   */
> > -extern int emulate_step(struct pt_regs *regs, unsigned int instr);
> > +extern int emulate_step(struct pt_regs *regs, unsigned int instr,
> > +                     unsigned int sufx);
> >
> >  /*
> >   * Emulate a load or store instruction by reading/writing the
> > diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
> > index 15002b51ff18..bc585399e0c7 100644
> > --- a/arch/powerpc/include/asm/uaccess.h
> > +++ b/arch/powerpc/include/asm/uaccess.h
> > @@ -423,4 +423,34 @@ extern long __copy_from_user_flushcache(void *dst, const void __user *src,
> >  extern void memcpy_page_flushcache(char *to, struct page *page, size_t offset,
> >                          size_t len);
> >
> > +/*
> > + * When reading an instruction iff it is a prefix, the suffix needs to be also
> > + * loaded.
> > + */
> > +#define __get_user_instr(x, y, ptr)                  \
> > +({                                                   \
> > +     long __gui_ret = 0;                             \
> > +     y = 0;                                          \
> > +     __gui_ret = __get_user(x, ptr);                 \
> > +     if (!__gui_ret) {                               \
> > +             if (IS_PREFIX(x))                       \
> > +                     __gui_ret = __get_user(y, ptr + 1);     \
> > +     }                                               \
> > +                                                     \
> > +     __gui_ret;                                      \
> > +})
> > +
> > +#define __get_user_instr_inatomic(x, y, ptr)         \
> > +({                                                   \
> > +     long __gui_ret = 0;                             \
> > +     y = 0;                                          \
> > +     __gui_ret = __get_user_inatomic(x, ptr);        \
> > +     if (!__gui_ret) {                               \
> > +             if (IS_PREFIX(x))                       \
> > +                     __gui_ret = __get_user_inatomic(y, ptr + 1);    \
> > +     }                                               \
> > +                                                     \
> > +     __gui_ret;                                      \
> > +})
> > +
> >  #endif       /* _ARCH_POWERPC_UACCESS_H */
> > diff --git a/arch/powerpc/kernel/align.c b/arch/powerpc/kernel/align.c
> > index 92045ed64976..245e79792a01 100644
> > --- a/arch/powerpc/kernel/align.c
> > +++ b/arch/powerpc/kernel/align.c
> > @@ -334,7 +334,7 @@ int fix_alignment(struct pt_regs *regs)
> >       if ((instr & 0xfc0006fe) == (PPC_INST_COPY & 0xfc0006fe))
> >               return -EIO;
> >
> > -     r = analyse_instr(&op, regs, instr);
> > +     r = analyse_instr(&op, regs, instr, 0);
> >       if (r < 0)
> >               return -EINVAL;
> >
> > diff --git a/arch/powerpc/kernel/hw_breakpoint.c b/arch/powerpc/kernel/hw_breakpoint.c
> > index 58ce3d37c2a3..f4530961998c 100644
> > --- a/arch/powerpc/kernel/hw_breakpoint.c
> > +++ b/arch/powerpc/kernel/hw_breakpoint.c
> > @@ -248,7 +248,7 @@ static bool stepping_handler(struct pt_regs *regs, struct perf_event *bp,
> >       if (__get_user_inatomic(instr, (unsigned int *)regs->nip))
> >               goto fail;
> >
> > -     ret = analyse_instr(&op, regs, instr);
> > +     ret = analyse_instr(&op, regs, instr, 0);
> >       type = GETTYPE(op.type);
> >       size = GETSIZE(op.type);
> >
> > @@ -272,7 +272,7 @@ static bool stepping_handler(struct pt_regs *regs, struct perf_event *bp,
> >               return false;
> >       }
> >
> > -     if (!emulate_step(regs, instr))
> > +     if (!emulate_step(regs, instr, 0))
> >               goto fail;
> >
> >       return true;
> > diff --git a/arch/powerpc/kernel/kprobes.c b/arch/powerpc/kernel/kprobes.c
> > index 2d27ec4feee4..7303fe3856cc 100644
> > --- a/arch/powerpc/kernel/kprobes.c
> > +++ b/arch/powerpc/kernel/kprobes.c
> > @@ -219,7 +219,7 @@ static int try_to_emulate(struct kprobe *p, struct pt_regs *regs)
> >       unsigned int insn = *p->ainsn.insn;
> >
> >       /* regs->nip is also adjusted if emulate_step returns 1 */
> > -     ret = emulate_step(regs, insn);
> > +     ret = emulate_step(regs, insn, 0);
> >       if (ret > 0) {
> >               /*
> >                * Once this instruction has been boosted
> > diff --git a/arch/powerpc/kernel/mce_power.c b/arch/powerpc/kernel/mce_power.c
> > index 1cbf7f1a4e3d..d862bb549158 100644
> > --- a/arch/powerpc/kernel/mce_power.c
> > +++ b/arch/powerpc/kernel/mce_power.c
> > @@ -374,7 +374,7 @@ static int mce_find_instr_ea_and_phys(struct pt_regs *regs, uint64_t *addr,
> >       if (pfn != ULONG_MAX) {
> >               instr_addr = (pfn << PAGE_SHIFT) + (regs->nip & ~PAGE_MASK);
> >               instr = *(unsigned int *)(instr_addr);
> > -             if (!analyse_instr(&op, &tmp, instr)) {
> > +             if (!analyse_instr(&op, &tmp, instr, 0)) {
> >                       pfn = addr_to_pfn(regs, op.ea);
> >                       *addr = op.ea;
> >                       *phys_addr = (pfn << PAGE_SHIFT);
> > diff --git a/arch/powerpc/kernel/optprobes.c b/arch/powerpc/kernel/optprobes.c
> > index 024f7aad1952..82dc8a589c87 100644
> > --- a/arch/powerpc/kernel/optprobes.c
> > +++ b/arch/powerpc/kernel/optprobes.c
> > @@ -100,7 +100,7 @@ static unsigned long can_optimize(struct kprobe *p)
> >        * and that can be emulated.
> >        */
> >       if (!is_conditional_branch(*p->ainsn.insn) &&
> > -                     analyse_instr(&op, &regs, *p->ainsn.insn) == 1) {
> > +                     analyse_instr(&op, &regs, *p->ainsn.insn, 0) == 1) {
> >               emulate_update_regs(&regs, &op);
> >               nip = regs.nip;
> >       }
> > diff --git a/arch/powerpc/kernel/uprobes.c b/arch/powerpc/kernel/uprobes.c
> > index 1cfef0e5fec5..ab1077dc6148 100644
> > --- a/arch/powerpc/kernel/uprobes.c
> > +++ b/arch/powerpc/kernel/uprobes.c
> > @@ -173,7 +173,7 @@ bool arch_uprobe_skip_sstep(struct arch_uprobe *auprobe, struct pt_regs *regs)
> >        * emulate_step() returns 1 if the insn was successfully emulated.
> >        * For all other cases, we need to single-step in hardware.
> >        */
> > -     ret = emulate_step(regs, auprobe->insn);
> > +     ret = emulate_step(regs, auprobe->insn, 0);
> >       if (ret > 0)
> >               return true;
> >
> > diff --git a/arch/powerpc/kvm/emulate_loadstore.c b/arch/powerpc/kvm/emulate_loadstore.c
> > index 2e496eb86e94..fcab1f31b48d 100644
> > --- a/arch/powerpc/kvm/emulate_loadstore.c
> > +++ b/arch/powerpc/kvm/emulate_loadstore.c
> > @@ -100,7 +100,7 @@ int kvmppc_emulate_loadstore(struct kvm_vcpu *vcpu)
> >
> >       emulated = EMULATE_FAIL;
> >       vcpu->arch.regs.msr = vcpu->arch.shared->msr;
> > -     if (analyse_instr(&op, &vcpu->arch.regs, inst) == 0) {
> > +     if (analyse_instr(&op, &vcpu->arch.regs, inst, 0) == 0) {
> >               int type = op.type & INSTR_TYPE_MASK;
> >               int size = GETSIZE(op.type);
> >
> > diff --git a/arch/powerpc/lib/sstep.c b/arch/powerpc/lib/sstep.c
> > index c077acb983a1..ade3f5eba2e5 100644
> > --- a/arch/powerpc/lib/sstep.c
> > +++ b/arch/powerpc/lib/sstep.c
> > @@ -1163,7 +1163,7 @@ static nokprobe_inline int trap_compare(long v1, long v2)
> >   * otherwise.
> >   */
> >  int analyse_instr(struct instruction_op *op, const struct pt_regs *regs,
> > -               unsigned int instr)
> > +               unsigned int instr, unsigned int sufx)
>
> I know we really like shortenings in arch/powerpc, but I think we can
> afford the two extra characters to spell 'suffix' in full :)
>
'suffix' was what I used initially but somewhere along the line
I found it looked unbalanced to see the abbreviation inst{r,} in the same
context as the unabbreviated 'suffix'. Happy to change it if it is clearer.

> >  {
> >       unsigned int opcode, ra, rb, rc, rd, spr, u;
> >       unsigned long int imm;
> > @@ -2756,7 +2756,8 @@ void emulate_update_regs(struct pt_regs *regs, struct instruction_op *op)
> >  {
> >       unsigned long next_pc;
> >
> > -     next_pc = truncate_if_32bit(regs->msr, regs->nip + 4);
> > +     next_pc = truncate_if_32bit(regs->msr,
> > +                                 regs->nip + ((op->type & PREFIXED) ? 8 : 4));
>
> I know you only use it twice, but this is super ugly - could you add a
> macro like IS_PREFIXED_TYPE? or even something like
> #define OP_TYPE_LENGTH(x) (((op)->type & PREFIXED) ? 8 : 4)
Yes that would be nicer.
>
> >       switch (GETTYPE(op->type)) {
> >       case COMPUTE:
> >               if (op->type & SETREG)
> > @@ -3101,14 +3102,14 @@ NOKPROBE_SYMBOL(emulate_loadstore);
> >   * or -1 if the instruction is one that should not be stepped,
> >   * such as an rfid, or a mtmsrd that would clear MSR_RI.
> >   */
> > -int emulate_step(struct pt_regs *regs, unsigned int instr)
> > +int emulate_step(struct pt_regs *regs, unsigned int instr, unsigned int sufx)
> >  {
> >       struct instruction_op op;
> >       int r, err, type;
> >       unsigned long val;
> >       unsigned long ea;
> >
> > -     r = analyse_instr(&op, regs, instr);
> > +     r = analyse_instr(&op, regs, instr, sufx);
> >       if (r < 0)
> >               return r;
> >       if (r > 0) {
> > @@ -3200,7 +3201,8 @@ int emulate_step(struct pt_regs *regs, unsigned int instr)
> >       return 0;
> >
> >   instr_done:
> > -     regs->nip = truncate_if_32bit(regs->msr, regs->nip + 4);
> > +     regs->nip = truncate_if_32bit(regs->msr,
> > +                                   regs->nip + ((op.type & PREFIXED) ? 8 : 4));
> >       return 1;
> >  }
> >  NOKPROBE_SYMBOL(emulate_step);
> > diff --git a/arch/powerpc/lib/test_emulate_step.c b/arch/powerpc/lib/test_emulate_step.c
> > index 42347067739c..9288dc6fc715 100644
> > --- a/arch/powerpc/lib/test_emulate_step.c
> > +++ b/arch/powerpc/lib/test_emulate_step.c
> > @@ -103,7 +103,7 @@ static void __init test_ld(void)
> >       regs.gpr[3] = (unsigned long) &a;
> >
> >       /* ld r5, 0(r3) */
> > -     stepped = emulate_step(&regs, TEST_LD(5, 3, 0));
> > +     stepped = emulate_step(&regs, TEST_LD(5, 3, 0), 0);
>
> I wonder if it would be clearer if we had something like
> #define NO_SUFFIX 0
It probably would be.

>
> >
> >       if (stepped == 1 && regs.gpr[5] == a)
> >               show_result("ld", "PASS");
> > @@ -121,7 +121,7 @@ static void __init test_lwz(void)
> >       regs.gpr[3] = (unsigned long) &a;
> >
> >       /* lwz r5, 0(r3) */
> > -     stepped = emulate_step(&regs, TEST_LWZ(5, 3, 0));
> > +     stepped = emulate_step(&regs, TEST_LWZ(5, 3, 0), 0);
> >
> >       if (stepped == 1 && regs.gpr[5] == a)
> >               show_result("lwz", "PASS");
> > @@ -141,7 +141,7 @@ static void __init test_lwzx(void)
> >       regs.gpr[5] = 0x8765;
> >
> >       /* lwzx r5, r3, r4 */
> > -     stepped = emulate_step(&regs, TEST_LWZX(5, 3, 4));
> > +     stepped = emulate_step(&regs, TEST_LWZX(5, 3, 4), 0);
> >       if (stepped == 1 && regs.gpr[5] == a[2])
> >               show_result("lwzx", "PASS");
> >       else
> > @@ -159,7 +159,7 @@ static void __init test_std(void)
> >       regs.gpr[5] = 0x5678;
> >
> >       /* std r5, 0(r3) */
> > -     stepped = emulate_step(&regs, TEST_STD(5, 3, 0));
> > +     stepped = emulate_step(&regs, TEST_STD(5, 3, 0), 0);
> >       if (stepped == 1 || regs.gpr[5] == a)
> >               show_result("std", "PASS");
> >       else
> > @@ -184,7 +184,7 @@ static void __init test_ldarx_stdcx(void)
> >       regs.gpr[5] = 0x5678;
> >
> >       /* ldarx r5, r3, r4, 0 */
> > -     stepped = emulate_step(&regs, TEST_LDARX(5, 3, 4, 0));
> > +     stepped = emulate_step(&regs, TEST_LDARX(5, 3, 4, 0), 0);
> >
> >       /*
> >        * Don't touch 'a' here. Touching 'a' can do Load/store
> > @@ -202,7 +202,7 @@ static void __init test_ldarx_stdcx(void)
> >       regs.gpr[5] = 0x9ABC;
> >
> >       /* stdcx. r5, r3, r4 */
> > -     stepped = emulate_step(&regs, TEST_STDCX(5, 3, 4));
> > +     stepped = emulate_step(&regs, TEST_STDCX(5, 3, 4), 0);
> >
> >       /*
> >        * Two possible scenarios that indicates successful emulation
> > @@ -242,7 +242,7 @@ static void __init test_lfsx_stfsx(void)
> >       regs.gpr[4] = 0;
> >
> >       /* lfsx frt10, r3, r4 */
> > -     stepped = emulate_step(&regs, TEST_LFSX(10, 3, 4));
> > +     stepped = emulate_step(&regs, TEST_LFSX(10, 3, 4), 0);
> >
> >       if (stepped == 1)
> >               show_result("lfsx", "PASS");
> > @@ -255,7 +255,7 @@ static void __init test_lfsx_stfsx(void)
> >       c.a = 678.91;
> >
> >       /* stfsx frs10, r3, r4 */
> > -     stepped = emulate_step(&regs, TEST_STFSX(10, 3, 4));
> > +     stepped = emulate_step(&regs, TEST_STFSX(10, 3, 4), 0);
> >
> >       if (stepped == 1 && c.b == cached_b)
> >               show_result("stfsx", "PASS");
> > @@ -285,7 +285,7 @@ static void __init test_lfdx_stfdx(void)
> >       regs.gpr[4] = 0;
> >
> >       /* lfdx frt10, r3, r4 */
> > -     stepped = emulate_step(&regs, TEST_LFDX(10, 3, 4));
> > +     stepped = emulate_step(&regs, TEST_LFDX(10, 3, 4), 0);
> >
> >       if (stepped == 1)
> >               show_result("lfdx", "PASS");
> > @@ -298,7 +298,7 @@ static void __init test_lfdx_stfdx(void)
> >       c.a = 987654.32;
> >
> >       /* stfdx frs10, r3, r4 */
> > -     stepped = emulate_step(&regs, TEST_STFDX(10, 3, 4));
> > +     stepped = emulate_step(&regs, TEST_STFDX(10, 3, 4), 0);
> >
> >       if (stepped == 1 && c.b == cached_b)
> >               show_result("stfdx", "PASS");
> > @@ -344,7 +344,7 @@ static void __init test_lvx_stvx(void)
> >       regs.gpr[4] = 0;
> >
> >       /* lvx vrt10, r3, r4 */
> > -     stepped = emulate_step(&regs, TEST_LVX(10, 3, 4));
> > +     stepped = emulate_step(&regs, TEST_LVX(10, 3, 4), 0);
> >
> >       if (stepped == 1)
> >               show_result("lvx", "PASS");
> > @@ -360,7 +360,7 @@ static void __init test_lvx_stvx(void)
> >       c.b[3] = 498532;
> >
> >       /* stvx vrs10, r3, r4 */
> > -     stepped = emulate_step(&regs, TEST_STVX(10, 3, 4));
> > +     stepped = emulate_step(&regs, TEST_STVX(10, 3, 4), 0);
> >
> >       if (stepped == 1 && cached_b[0] == c.b[0] && cached_b[1] == c.b[1] &&
> >           cached_b[2] == c.b[2] && cached_b[3] == c.b[3])
> > @@ -401,7 +401,7 @@ static void __init test_lxvd2x_stxvd2x(void)
> >       regs.gpr[4] = 0;
> >
> >       /* lxvd2x vsr39, r3, r4 */
> > -     stepped = emulate_step(&regs, TEST_LXVD2X(39, 3, 4));
> > +     stepped = emulate_step(&regs, TEST_LXVD2X(39, 3, 4), 0);
> >
> >       if (stepped == 1 && cpu_has_feature(CPU_FTR_VSX)) {
> >               show_result("lxvd2x", "PASS");
> > @@ -421,7 +421,7 @@ static void __init test_lxvd2x_stxvd2x(void)
> >       c.b[3] = 4;
> >
> >       /* stxvd2x vsr39, r3, r4 */
> > -     stepped = emulate_step(&regs, TEST_STXVD2X(39, 3, 4));
> > +     stepped = emulate_step(&regs, TEST_STXVD2X(39, 3, 4), 0);
> >
> >       if (stepped == 1 && cached_b[0] == c.b[0] && cached_b[1] == c.b[1] &&
> >           cached_b[2] == c.b[2] && cached_b[3] == c.b[3] &&
> > @@ -848,7 +848,7 @@ static int __init emulate_compute_instr(struct pt_regs *regs,
> >       if (!regs || !instr)
> >               return -EINVAL;
> >
> > -     if (analyse_instr(&op, regs, instr) != 1 ||
> > +     if (analyse_instr(&op, regs, instr, 0) != 1 ||
> >           GETTYPE(op.type) != COMPUTE) {
> >               pr_info("emulation failed, instruction = 0x%08x\n", instr);
> >               return -EFAULT;
> > diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
> > index a7056049709e..f47bd843dc52 100644
> > --- a/arch/powerpc/xmon/xmon.c
> > +++ b/arch/powerpc/xmon/xmon.c
> > @@ -705,7 +705,7 @@ static int xmon_core(struct pt_regs *regs, int fromipi)
> >       if ((regs->msr & (MSR_IR|MSR_PR|MSR_64BIT)) == (MSR_IR|MSR_64BIT)) {
> >               bp = at_breakpoint(regs->nip);
> >               if (bp != NULL) {
> > -                     int stepped = emulate_step(regs, bp->instr[0]);
> > +                     int stepped = emulate_step(regs, bp->instr[0], 0);
> >                       if (stepped == 0) {
> >                               regs->nip = (unsigned long) &bp->instr[0];
> >                               atomic_inc(&bp->ref_count);
> > @@ -1170,7 +1170,7 @@ static int do_step(struct pt_regs *regs)
> >       /* 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) {
> > -                     stepped = emulate_step(regs, instr);
> > +                     stepped = emulate_step(regs, instr, 0);
> >                       if (stepped < 0) {
> >                               printf("Couldn't single-step %s instruction\n",
> >                                      (IS_RFID(instr)? "rfid": "mtmsrd"));
> > --
> > 2.20.1


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