[PATCH 05/18] powerpc sstep: Prepare to support prefixed instructions
Jordan Niethe
jniethe5 at gmail.com
Fri Dec 20 16:17:50 AEDT 2019
On Thu, Dec 19, 2019 at 1:15 AM 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);
> >
>
> I'm not saying this is necessarily better, but did you consider:
>
> - making instr 64 bits and using masking and shifting macros to get the
> prefix and suffix?
>
> - defining an instruction type/struct/union/whatever that contains both
> halves in one object?
>
> I'm happy to be told that it ends up being way, way uglier/worse/etc,
> but I just thought I'd ask.
>
> Regards,
> Daniel
It is a good question and something I thought and am not completely confident
that this approach is the best. Basically what I ended up thinking was that
the prefixed instructions were a bit of a special case, and by doing
it like this
the normal word instructions would just carry on the same as before.
I can see this is a pretty flimsy reason, so I am happy for suggestions as
to what would end up being clearer.
>
> > /*
> > * 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, ®s, *p->ainsn.insn) == 1) {
> > + analyse_instr(&op, ®s, *p->ainsn.insn, 0) == 1) {
> > emulate_update_regs(®s, &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)
> > {
> > 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));
> > 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(®s, TEST_LD(5, 3, 0));
> > + stepped = emulate_step(®s, TEST_LD(5, 3, 0), 0);
> >
> > 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(®s, TEST_LWZ(5, 3, 0));
> > + stepped = emulate_step(®s, 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(®s, TEST_LWZX(5, 3, 4));
> > + stepped = emulate_step(®s, 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(®s, TEST_STD(5, 3, 0));
> > + stepped = emulate_step(®s, 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(®s, TEST_LDARX(5, 3, 4, 0));
> > + stepped = emulate_step(®s, 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(®s, TEST_STDCX(5, 3, 4));
> > + stepped = emulate_step(®s, 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(®s, TEST_LFSX(10, 3, 4));
> > + stepped = emulate_step(®s, 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(®s, TEST_STFSX(10, 3, 4));
> > + stepped = emulate_step(®s, 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(®s, TEST_LFDX(10, 3, 4));
> > + stepped = emulate_step(®s, 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(®s, TEST_STFDX(10, 3, 4));
> > + stepped = emulate_step(®s, 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(®s, TEST_LVX(10, 3, 4));
> > + stepped = emulate_step(®s, 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(®s, TEST_STVX(10, 3, 4));
> > + stepped = emulate_step(®s, 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(®s, TEST_LXVD2X(39, 3, 4));
> > + stepped = emulate_step(®s, 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(®s, TEST_STXVD2X(39, 3, 4));
> > + stepped = emulate_step(®s, 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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