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Subject: Re: [PATCH v1 2/2] powerpc: Enable OPTPROBES on PPC32
To:     "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Paul Mackerras <paulus@samba.org>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
References: <e1723a06c5a26398ff03cb669ec99de2516045a9.1617701875.git.christophe.leroy@csgroup.eu>
 <28730d147adeaa6c2d0c98d0aa9e17e9e4bd043a.1617701875.git.christophe.leroy@csgroup.eu>
 <1618900760.son2fwciv1.naveen@linux.ibm.com>
From:   Christophe Leroy <christophe.leroy@csgroup.eu>
Message-ID: <db3b71f3-2554-69b0-6ef9-a70e31d034b6@csgroup.eu>
Date:   Tue, 20 Apr 2021 15:37:06 +0200
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Le 20/04/2021 à 08:51, Naveen N. Rao a écrit :
> Christophe Leroy wrote:
>> For that, create a 32 bits version of patch_imm64_load_insns()
>> and create a patch_imm_load_insns() which calls
>> patch_imm32_load_insns() on PPC32 and patch_imm64_load_insns()
>> on PPC64.
>>
>> Adapt optprobes_head.S for PPC32. Use PPC_LL/PPC_STL macros instead
>> of raw ld/std, opt out things linked to paca and use stmw/lmw to
>> save/restore registers.
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
>> ---
>>  arch/powerpc/Kconfig                 |  2 +-
>>  arch/powerpc/kernel/optprobes.c      | 24 +++++++++++++--
>>  arch/powerpc/kernel/optprobes_head.S | 46 +++++++++++++++++++---------
>>  3 files changed, 53 insertions(+), 19 deletions(-)
> 
> Thanks for adding support for ppc32. It is good to see that it works without too many changes.
> 
>>
>> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
>> index c1344c05226c..49b538e54efb 100644
>> --- a/arch/powerpc/Kconfig
>> +++ b/arch/powerpc/Kconfig
>> @@ -227,7 +227,7 @@ config PPC
>>      select HAVE_MOD_ARCH_SPECIFIC
>>      select HAVE_NMI                if PERF_EVENTS || (PPC64 && PPC_BOOK3S)
>>      select HAVE_HARDLOCKUP_DETECTOR_ARCH    if PPC64 && PPC_BOOK3S && SMP
>> -    select HAVE_OPTPROBES            if PPC64
>> +    select HAVE_OPTPROBES
>>      select HAVE_PERF_EVENTS
>>      select HAVE_PERF_EVENTS_NMI        if PPC64
>>      select HAVE_HARDLOCKUP_DETECTOR_PERF    if PERF_EVENTS && HAVE_PERF_EVENTS_NMI && 
>> !HAVE_HARDLOCKUP_DETECTOR_ARCH
>> diff --git a/arch/powerpc/kernel/optprobes.c b/arch/powerpc/kernel/optprobes.c
>> index 58fdb9f66e0f..cdf87086fa33 100644
>> --- a/arch/powerpc/kernel/optprobes.c
>> +++ b/arch/powerpc/kernel/optprobes.c
>> @@ -141,11 +141,21 @@ void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
>>      }
>>  }
>>
>> +static void patch_imm32_load_insns(unsigned long val, int reg, kprobe_opcode_t *addr)
>> +{
>> +    patch_instruction((struct ppc_inst *)addr,
>> +              ppc_inst(PPC_RAW_LIS(reg, IMM_H(val))));
>> +    addr++;
>> +
>> +    patch_instruction((struct ppc_inst *)addr,
>> +              ppc_inst(PPC_RAW_ORI(reg, reg, IMM_L(val))));
>> +}
>> +
>>  /*
>>   * Generate instructions to load provided immediate 64-bit value
>>   * to register 'reg' and patch these instructions at 'addr'.
>>   */
>> -static void patch_imm64_load_insns(unsigned long val, int reg, kprobe_opcode_t *addr)
>> +static void patch_imm64_load_insns(unsigned long long val, int reg, kprobe_opcode_t *addr)
> 
> Do you really need this?

Without it I get:

                  from arch/powerpc/kernel/optprobes.c:8:
arch/powerpc/kernel/optprobes.c: In function 'patch_imm64_load_insns':
arch/powerpc/kernel/optprobes.c:163:14: error: right shift count >= width of type 
[-Werror=shift-count-overflow]
   163 |        ((val >> 48) & 0xffff)));
       |              ^~
./arch/powerpc/include/asm/inst.h:69:48: note: in definition of macro 'ppc_inst'
    69 | #define ppc_inst(x) ((struct ppc_inst){ .val = x })
       |                                                ^
arch/powerpc/kernel/optprobes.c:169:31: error: right shift count >= width of type 
[-Werror=shift-count-overflow]
   169 |        ___PPC_RS(reg) | ((val >> 32) & 0xffff)));
       |                               ^~
./arch/powerpc/include/asm/inst.h:69:48: note: in definition of macro 'ppc_inst'
    69 | #define ppc_inst(x) ((struct ppc_inst){ .val = x })
       |                                                ^


> 
>>  {
>>      /* lis reg,(op)@highest */
>>      patch_instruction((struct ppc_inst *)addr,
>> @@ -177,6 +187,14 @@ static void patch_imm64_load_insns(unsigned long val, int reg, kprobe_opcode_t *
>>                     ___PPC_RS(reg) | (val & 0xffff)));
>>  }
>>
>> +static void patch_imm_load_insns(unsigned long val, int reg, kprobe_opcode_t *addr)
>> +{
>> +    if (IS_ENABLED(CONFIG_PPC64))
>> +        patch_imm64_load_insns(val, reg, addr);
>> +    else
>> +        patch_imm32_load_insns(val, reg, addr);
>> +}
>> +
>>  int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
>>  {
>>      struct ppc_inst branch_op_callback, branch_emulate_step, temp;
>> @@ -230,7 +248,7 @@ int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
>>       * Fixup the template with instructions to:
>>       * 1. load the address of the actual probepoint
>>       */
>> -    patch_imm64_load_insns((unsigned long)op, 3, buff + TMPL_OP_IDX);
>> +    patch_imm_load_insns((unsigned long)op, 3, buff + TMPL_OP_IDX);
>>
>>      /*
>>       * 2. branch to optimized_callback() and emulate_step()
>> @@ -264,7 +282,7 @@ int arch_prepare_optimized_kprobe(struct optimized_kprobe *op, struct kprobe *p)
>>       * 3. load instruction to be emulated into relevant register, and
>>       */
>>      temp = ppc_inst_read((struct ppc_inst *)p->ainsn.insn);
>> -    patch_imm64_load_insns(ppc_inst_as_ulong(temp), 4, buff + TMPL_INSN_IDX);
>> +    patch_imm_load_insns(ppc_inst_as_ulong(temp), 4, buff + TMPL_INSN_IDX);
>>
>>      /*
>>       * 4. branch back from trampoline
>> diff --git a/arch/powerpc/kernel/optprobes_head.S b/arch/powerpc/kernel/optprobes_head.S
>> index ff8ba4d3824d..49f31e554573 100644
>> --- a/arch/powerpc/kernel/optprobes_head.S
>> +++ b/arch/powerpc/kernel/optprobes_head.S
>> @@ -30,39 +30,47 @@ optinsn_slot:
>>      .global optprobe_template_entry
>>  optprobe_template_entry:
>>      /* Create an in-memory pt_regs */
>> -    stdu    r1,-INT_FRAME_SIZE(r1)
>> +    PPC_STLU    r1,-INT_FRAME_SIZE(r1)
>>      SAVE_GPR(0,r1)
>>      /* Save the previous SP into stack */
>>      addi    r0,r1,INT_FRAME_SIZE
>> -    std    r0,GPR1(r1)
>> +    PPC_STL    r0,GPR1(r1)
>> +#ifdef CONFIG_PPC64
>>      SAVE_10GPRS(2,r1)
>>      SAVE_10GPRS(12,r1)
>>      SAVE_10GPRS(22,r1)
>> +#else
>> +    stmw    r2, GPR2(r1)
>> +#endif
>>      /* Save SPRS */
>>      mfmsr    r5
>> -    std    r5,_MSR(r1)
>> +    PPC_STL    r5,_MSR(r1)
>>      li    r5,0x700
>> -    std    r5,_TRAP(r1)
>> +    PPC_STL    r5,_TRAP(r1)
>>      li    r5,0
>> -    std    r5,ORIG_GPR3(r1)
>> -    std    r5,RESULT(r1)
>> +    PPC_STL    r5,ORIG_GPR3(r1)
>> +    PPC_STL    r5,RESULT(r1)
>>      mfctr    r5
>> -    std    r5,_CTR(r1)
>> +    PPC_STL    r5,_CTR(r1)
>>      mflr    r5
>> -    std    r5,_LINK(r1)
>> +    PPC_STL    r5,_LINK(r1)
>>      mfspr    r5,SPRN_XER
>> -    std    r5,_XER(r1)
>> +    PPC_STL    r5,_XER(r1)
>>      mfcr    r5
>> -    std    r5,_CCR(r1)
>> +    PPC_STL    r5,_CCR(r1)
>> +#ifdef CONFIG_PPC64
>>      lbz     r5,PACAIRQSOFTMASK(r13)
>>      std     r5,SOFTE(r1)
>> +#endif
>>
>>      /*
>>       * We may get here from a module, so load the kernel TOC in r2.
>>       * The original TOC gets restored when pt_regs is restored
>>       * further below.
>>       */
>> +#ifdef CONFIG_PPC64
>>      ld    r2,PACATOC(r13)
>> +#endif
> 
> Are the ISA and ABI documents for ppc32 available publicly? 

ABI: https://wiki.raptorcs.com/w/images/0/03/Power-Arch-32-bit-ABI-supp-1.0-Unified.pdf

ISA: https://www.nxp.com/files-static/product/doc/MPCFPE32B.pdf


> I would have thought that the TOC issues 
> apply to ppc32 as well, but want to understand why this isn't a problem there.

r2 is the pointer to 'current' on PPC32.

No TOC.


> 
>>
>>      .global optprobe_template_op_address
>>  optprobe_template_op_address:
>> @@ -72,9 +80,11 @@ optprobe_template_op_address:
>>       */
>>      nop
>>      nop
>> +#ifdef CONFIG_PPC64
>>      nop
>>      nop
>>      nop
>> +#endif
>>      /* 2. pt_regs pointer in r4 */
>>      addi    r4,r1,STACK_FRAME_OVERHEAD
>>
>> @@ -94,9 +104,11 @@ optprobe_template_insn:
>>      /* 2, Pass instruction to be emulated in r4 */
>>      nop
>>      nop
>> +#ifdef CONFIG_PPC64
>>      nop
>>      nop
>>      nop
>> +#endif
> 
> It would be nice to put these behind a macro so as to avoid these #ifdef blocks here, as well as 
> with the register save/restore sequence.
> 

Will see what I can do

Christophe