Re: [PATCH v1 13/22] powerpc/ftrace: Use PPC_RAW_xxx() macros instead of opencoding.

[Christophe Leroy]

Le 18/04/2022 à 09:38, Naveen N. Rao a écrit :
> Christophe Leroy wrote:
>> PPC_RAW_xxx() macros are self explanatory and less error prone
>> than open coding.
>>
>> Use them in ftrace.c
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@xxxxxxxxxx>
>> ---
>>  arch/powerpc/include/asm/ppc-opcode.h |  3 +++
>>  arch/powerpc/kernel/trace/ftrace.c    | 32 +++++++++------------------
>>  2 files changed, 14 insertions(+), 21 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/ppc-opcode.h 
>> b/arch/powerpc/include/asm/ppc-opcode.h
>> index 82f1f0041c6f..281754aca0a3 100644
>> --- a/arch/powerpc/include/asm/ppc-opcode.h
>> +++ b/arch/powerpc/include/asm/ppc-opcode.h
>> @@ -294,6 +294,8 @@
>>  #define PPC_INST_BL            0x48000001
>>  #define PPC_INST_BRANCH_COND        0x40800000
>>
>> +#define PPC_INST_OFFSET24_MASK        0x03fffffc
> 
> This corresponds to the LI field, per the ISA. See section 8.1.2/1.7: 
> 'Instruction Fields'. Would it be better to name it PPC_INST_LI_MASK?

Isn't there a risk of confusing with the 'li' instruction ? Like we 
could have PPC_INST_LI just like we have PPC_INST_ADD ?



> 
>> +
>>  /* Prefixes */
>>  #define PPC_INST_LFS            0xc0000000
>>  #define PPC_INST_STFS            0xd0000000
>> @@ -572,6 +574,7 @@
>>  #define PPC_RAW_EIEIO()            (0x7c0006ac)
>>
>>  #define PPC_RAW_BRANCH(addr)        (PPC_INST_BRANCH | ((addr) & 
>> 0x03fffffc))
>> +#define PPC_RAW_BL(offset)        (0x48000001 | ((offset) & 
>> PPC_INST_OFFSET24_MASK))
>>
>>  /* Deal with instructions that older assemblers aren't aware of */
>>  #define    PPC_BCCTR_FLUSH        stringify_in_c(.long 
>> PPC_INST_BCCTR_FLUSH)
>> diff --git a/arch/powerpc/kernel/trace/ftrace.c 
>> b/arch/powerpc/kernel/trace/ftrace.c
>> index fdc0412c1d8a..afb1d12838c9 100644
>> --- a/arch/powerpc/kernel/trace/ftrace.c
>> +++ b/arch/powerpc/kernel/trace/ftrace.c
>> @@ -90,19 +90,19 @@ static int test_24bit_addr(unsigned long ip, 
>> unsigned long addr)
>>
>>  static int is_bl_op(ppc_inst_t op)
>>  {
>> -    return (ppc_inst_val(op) & 0xfc000003) == 0x48000001;
>> +    return (ppc_inst_val(op) & ~PPC_INST_OFFSET24_MASK) == 
>> PPC_RAW_BL(0);
>>  }
>>
>>  static int is_b_op(ppc_inst_t op)
>>  {
>> -    return (ppc_inst_val(op) & 0xfc000003) == 0x48000000;
>> +    return (ppc_inst_val(op) & ~PPC_INST_OFFSET24_MASK) == 
>> PPC_RAW_BRANCH(0);
>>  }
>>
>>  static unsigned long find_bl_target(unsigned long ip, ppc_inst_t op)
>>  {
>>      int offset;
>>
>> -    offset = (ppc_inst_val(op) & 0x03fffffc);
>> +    offset = (ppc_inst_val(op) & PPC_INST_OFFSET24_MASK);
>>      /* make it signed */
>>      if (offset & 0x02000000)
>>          offset |= 0xfe000000;
>> @@ -182,7 +182,7 @@ __ftrace_make_nop(struct module *mod,
>>       * Use a b +8 to jump over the load.
>>       */
>>
>> -    pop = ppc_inst(PPC_INST_BRANCH | 8);    /* b +8 */
>> +    pop = ppc_inst(PPC_RAW_BRANCH(8));    /* b +8 */
>>
>>      /*
>>       * Check what is in the next instruction. We can see ld 
>> r2,40(r1), but
>> @@ -394,17 +394,8 @@ int ftrace_make_nop(struct module *mod,
>>  static int
>>  expected_nop_sequence(void *ip, ppc_inst_t op0, ppc_inst_t op1)
>>  {
>> -    /*
>> -     * We expect to see:
>> -     *
>> -     * b +8
>> -     * ld r2,XX(r1)
>> -     *
>> -     * The load offset is different depending on the ABI. For simplicity
>> -     * just mask it out when doing the compare.
>> -     */
>> -    if (!ppc_inst_equal(op0, ppc_inst(0x48000008)) ||
>> -        (ppc_inst_val(op1) & 0xffff0000) != 0xe8410000)
>> +    if (!ppc_inst_equal(op0, ppc_inst(PPC_RAW_BRANCH(8))) ||
>> +        !ppc_inst_equal(op1, ppc_inst(PPC_INST_LD_TOC)))
> 
> It would be good to move PPC_INST_LD_TOC to ppc-opcode.h

It's not really just an instruction, it's closely linked to the ABI, so 
does it really belong to ppc-opcode.h ? Maybe it could be better to have 
it in ppc_asm.h instead, which already contains ABI related definitions ?

If we move it into ppc-opcode.h, then we also have to move 
R2_STACK_OFFSET. Or should we use STK_GOT defined in ppc_asm.h and drop 
R2_STACK_OFFSET ?

> 
>>          return 0;
>>      return 1;
>>  }
>> @@ -412,7 +403,6 @@ expected_nop_sequence(void *ip, ppc_inst_t op0, 
>> ppc_inst_t op1)
>>  static int
>>  expected_nop_sequence(void *ip, ppc_inst_t op0, ppc_inst_t op1)
>>  {
>> -    /* look for patched "NOP" on ppc64 with -mprofile-kernel or ppc32 */
>>      if (!ppc_inst_equal(op0, ppc_inst(PPC_RAW_NOP())))
>>          return 0;
>>      return 1;
>> @@ -738,11 +728,11 @@ int __init ftrace_dyn_arch_init(void)
>>      int i;
>>      unsigned int *tramp[] = { ftrace_tramp_text, ftrace_tramp_init };
>>      u32 stub_insns[] = {
>> -        0xe98d0000 | PACATOC,    /* ld      r12,PACATOC(r13)    */
>> -        0x3d8c0000,        /* addis   r12,r12,<high>    */
>> -        0x398c0000,        /* addi    r12,r12,<low>    */
>> -        0x7d8903a6,        /* mtctr   r12            */
>> -        0x4e800420,        /* bctr                */
>> +        PPC_RAW_LD(_R12, _R13, PACATOC),
>> +        PPC_RAW_ADDIS(_R12, _R12, 0),
>> +        PPC_RAW_ADDIS(_R12, _R12, 0),
> 
> This should be PPC_RAW_ADDI.
> 

Oops.

Christophe