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    Subject[PATCH 07/12] powerpc/ftrace: FTRACE_WITH_REGS implementation for ppc64le
    Date
    From: Torsten Duwe <duwe@lst.de>

    Implement FTRACE_WITH_REGS for powerpc64, on ELF ABI v2.
    Initial work started by Vojtech Pavlik, used with permission.

    * arch/powerpc/kernel/entry_64.S:
    - Implement an effective ftrace_caller that works from
    within the kernel binary as well as from modules.
    * arch/powerpc/kernel/ftrace.c:
    - be prepared to deal with ppc64 ELF ABI v2, especially
    calls to _mcount that result from gcc -mprofile-kernel
    - a little more error verbosity
    * arch/powerpc/kernel/module_64.c:
    - do not save the TOC pointer on the trampoline when the
    destination is ftrace_caller. This trampoline jump happens from
    a function prologue before a new stack frame is set up, so bad
    things may happen otherwise...
    - relax is_module_trampoline() to recognise the modified
    trampoline.

    Signed-off-by: Torsten Duwe <duwe@suse.de>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    ---
    arch/powerpc/include/asm/ftrace.h | 5 +++
    arch/powerpc/kernel/entry_64.S | 78 +++++++++++++++++++++++++++++++++++++++
    arch/powerpc/kernel/ftrace.c | 66 ++++++++++++++++++++++++++++++---
    arch/powerpc/kernel/module_64.c | 16 ++++++++
    4 files changed, 159 insertions(+), 6 deletions(-)

    Probably squash.

    diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h
    index ef89b1465573..50ca7585abe2 100644
    --- a/arch/powerpc/include/asm/ftrace.h
    +++ b/arch/powerpc/include/asm/ftrace.h
    @@ -46,6 +46,8 @@
    extern void _mcount(void);

    #ifdef CONFIG_DYNAMIC_FTRACE
    +# define FTRACE_ADDR ((unsigned long)ftrace_caller)
    +# define FTRACE_REGS_ADDR FTRACE_ADDR
    static inline unsigned long ftrace_call_adjust(unsigned long addr)
    {
    /* reloction of mcount call site is the same as the address */
    @@ -58,6 +60,9 @@ struct dyn_arch_ftrace {
    #endif /* CONFIG_DYNAMIC_FTRACE */
    #endif /* __ASSEMBLY__ */

    +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
    +#define ARCH_SUPPORTS_FTRACE_OPS 1
    +#endif
    #endif

    #if defined(CONFIG_FTRACE_SYSCALLS) && defined(CONFIG_PPC64) && !defined(__ASSEMBLY__)
    diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S
    index 9e77a2c8f218..149b659a25d9 100644
    --- a/arch/powerpc/kernel/entry_64.S
    +++ b/arch/powerpc/kernel/entry_64.S
    @@ -1148,6 +1148,7 @@ _GLOBAL(_mcount)
    mtlr r0
    bctr

    +#ifndef CC_USING_MPROFILE_KERNEL
    _GLOBAL_TOC(ftrace_caller)
    /* Taken from output of objdump from lib64/glibc */
    mflr r3
    @@ -1169,6 +1170,83 @@ _GLOBAL(ftrace_graph_stub)
    ld r0, 128(r1)
    mtlr r0
    addi r1, r1, 112
    +#else
    +_GLOBAL(ftrace_caller)
    + std r0,LRSAVE(r1)
    +#if defined(_CALL_ELF) && _CALL_ELF == 2
    + mflr r0
    + bl 2f
    +2: mflr r12
    + mtlr r0
    + mr r0,r2 /* save callee's TOC */
    + addis r2,r12,(.TOC.-ftrace_caller-12)@ha
    + addi r2,r2,(.TOC.-ftrace_caller-12)@l
    +#else
    + mr r0,r2
    +#endif
    + ld r12,LRSAVE(r1) /* get caller's address */
    +
    + stdu r1,-SWITCH_FRAME_SIZE(r1)
    +
    + std r12, _LINK(r1)
    + SAVE_8GPRS(0,r1)
    + std r0, 24(r1) /* save TOC */
    + SAVE_8GPRS(8,r1)
    + SAVE_8GPRS(16,r1)
    + SAVE_8GPRS(24,r1)
    +
    + addis r3,r2,function_trace_op@toc@ha
    + addi r3,r3,function_trace_op@toc@l
    + ld r5,0(r3)
    +
    + mflr r3
    + std r3, _NIP(r1)
    + std r3, 16(r1)
    + subi r3, r3, MCOUNT_INSN_SIZE
    + mfmsr r4
    + std r4, _MSR(r1)
    + mfctr r4
    + std r4, _CTR(r1)
    + mfxer r4
    + std r4, _XER(r1)
    + mr r4, r12
    + addi r6, r1 ,STACK_FRAME_OVERHEAD
    +
    +.globl ftrace_call
    +ftrace_call:
    + bl ftrace_stub
    + nop
    +
    + ld r3, _NIP(r1)
    + mtlr r3
    +
    + REST_8GPRS(0,r1)
    + REST_8GPRS(8,r1)
    + REST_8GPRS(16,r1)
    + REST_8GPRS(24,r1)
    +
    + addi r1, r1, SWITCH_FRAME_SIZE
    +
    + ld r12, LRSAVE(r1) /* get caller's address */
    + mtlr r12
    + mr r2,r0 /* restore callee's TOC */
    +
    +#ifdef CONFIG_FUNCTION_GRAPH_TRACER
    + stdu r1, -112(r1)
    +.globl ftrace_graph_call
    +ftrace_graph_call:
    + b ftrace_graph_stub
    +_GLOBAL(ftrace_graph_stub)
    + addi r1, r1, 112
    +#endif
    +
    + mflr r0 /* move this LR to CTR */
    + mtctr r0
    +
    + ld r0,LRSAVE(r1) /* restore callee's lr at _mcount site */
    + mtlr r0
    + bctr /* jump after _mcount site */
    +#endif /* CC_USING_MPROFILE_KERNEL */
    _GLOBAL(ftrace_stub)
    blr
    #else
    diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
    index a1d95f20b017..c6408a399ac6 100644
    --- a/arch/powerpc/kernel/ftrace.c
    +++ b/arch/powerpc/kernel/ftrace.c
    @@ -61,8 +61,11 @@ ftrace_modify_code(unsigned long ip, unsigned int old, unsigned int new)
    return -EFAULT;

    /* Make sure it is what we expect it to be */
    - if (replaced != old)
    + if (replaced != old) {
    + pr_err("%p: replaced (%#x) != old (%#x)",
    + (void *)ip, replaced, old);
    return -EINVAL;
    + }

    /* replace the text with the new text */
    if (patch_instruction((unsigned int *)ip, new))
    @@ -108,11 +111,13 @@ __ftrace_make_nop(struct module *mod,
    {
    unsigned long entry, ptr, tramp;
    unsigned long ip = rec->ip;
    - unsigned int op;
    + unsigned int op, pop;

    /* read where this goes */
    - if (probe_kernel_read(&op, (void *)ip, sizeof(int)))
    + if (probe_kernel_read(&op, (void *)ip, sizeof(int))) {
    + pr_err("Fetching opcode failed.\n");
    return -EFAULT;
    + }

    /* Make sure that that this is still a 24bit jump */
    if (!is_bl_op(op)) {
    @@ -152,10 +157,51 @@ __ftrace_make_nop(struct module *mod,
    *
    * Use a b +8 to jump over the load.
    */
    - op = 0x48000008; /* b +8 */

    - if (patch_instruction((unsigned int *)ip, op))
    + pop = PPC_INST_BRANCH | 8; /* b +8 */
    +
    + /*
    + * Check what is in the next instruction. We can see ld r2,40(r1), but
    + * on first pass after boot we will see mflr r0.
    + */
    + if (probe_kernel_read(&op, (void *)(ip+4), MCOUNT_INSN_SIZE)) {
    + pr_err("Fetching op failed.\n");
    + return -EFAULT;
    + }
    +
    + if (op != PPC_INST_LD_TOC)
    + {
    + unsigned int op0, op1;
    +
    + if (probe_kernel_read(&op0, (void *)(ip-8), MCOUNT_INSN_SIZE)) {
    + pr_err("Fetching op0 failed.\n");
    + return -EFAULT;
    + }
    +
    + if (probe_kernel_read(&op1, (void *)(ip-4), MCOUNT_INSN_SIZE)) {
    + pr_err("Fetching op1 failed.\n");
    + return -EFAULT;
    + }
    +
    + /* mflr r0 ; [ std r0,LRSAVE(r1) ]? */
    + if ( (op0 != PPC_INST_MFLR ||
    + op1 != PPC_INST_STD_LR)
    + && op1 != PPC_INST_MFLR )
    + {
    + pr_err("Unexpected instructions around bl _mcount\n"
    + "when enabling dynamic ftrace!\t"
    + "(%08x,%08x,bl,%08x)\n", op0, op1, op);
    + return -EINVAL;
    + }
    +
    + /* When using -mkernel_profile there is no load to jump over */
    + pop = PPC_INST_NOP;
    + }
    +
    + if (patch_instruction((unsigned int *)ip, pop)) {
    + pr_err("Patching NOP failed.\n");
    return -EPERM;
    + }

    return 0;
    }
    @@ -281,6 +327,14 @@ int ftrace_make_nop(struct module *mod,

    #ifdef CONFIG_MODULES
    #ifdef CONFIG_PPC64
    +#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
    +int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
    + unsigned long addr)
    +{
    + return ftrace_make_call(rec, addr);
    +}
    +#endif
    +
    /* Examine the existing instructions for __ftrace_make_call.
    * They should effectively be a NOP, and follow formal constraints,
    * depending on the ABI. Return false if they don't.
    @@ -348,7 +402,7 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)

    return 0;
    }
    -#else
    +#else /* !CONFIG_PPC64: */
    static int
    __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
    {
    diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
    index 495df4340623..a3a13fcfc99c 100644
    --- a/arch/powerpc/kernel/module_64.c
    +++ b/arch/powerpc/kernel/module_64.c
    @@ -139,6 +139,19 @@ static u32 ppc64_stub_insns[] = {
    0x4e800420 /* bctr */
    };

    +#ifdef CC_USING_MPROFILE_KERNEL
    +/* In case of _mcount calls or dynamic ftracing, Do not save the
    + * current callee's TOC (in R2) again into the original caller's stack
    + * frame during this trampoline hop. The stack frame already holds
    + * that of the original caller. _mcount and ftrace_caller will take
    + * care of this TOC value themselves.
    + */
    +#define SQUASH_TOC_SAVE_INSN(trampoline_addr) \
    + (((struct ppc64_stub_entry *)(trampoline_addr))->jump[2] = PPC_INST_NOP)
    +#else
    +#define SQUASH_TOC_SAVE_INSN(trampoline_addr)
    +#endif
    +
    #ifdef CONFIG_DYNAMIC_FTRACE
    int module_trampoline_target(struct module *mod, unsigned long addr,
    unsigned long *target)
    @@ -608,6 +621,9 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
    return -ENOENT;
    if (!restore_r2((u32 *)location + 1, me))
    return -ENOEXEC;
    + /* Squash the TOC saver for profiler calls */
    + if (!strcmp("_mcount", strtab+sym->st_name))
    + SQUASH_TOC_SAVE_INSN(value);
    } else
    value += local_entry_offset(sym);

    --
    2.5.0
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