[RFC] Kernel livepatching support in GCC

[libin]

在 2015/10/22 18:16, Szabolcs Nagy 写道:
> On 22/10/15 10:23, libin wrote:
>> From: Jiangjiji <jiangjiji@huawei.com>
>> Date: Sat, 10 Oct 2015 15:29:57 +0800
>> Subject: [PATCH] * gcc/config/aarch64/aarch64.opt: Add a new option.
>>   * gcc/config/aarch64/aarch64.c: Add some new functions and Macros.
>>   * gcc/config/aarch64/aarch64.h: Modify PROFILE_HOOK and FUNCTION_PROFILER.
>>
> 
> this patch might be worth submitting to gcc-patches.
> 

Ok, i will submit it to gcc-patches :)

> i assume this is not redundant with respect to the
> nop-padding work.
> 
>> Signed-off-by: Jiangjiji <jiangjiji@huawei.com>
>> Signed-off-by: Li Bin <huawei.libin@huawei.com>
>> ---
>>   gcc/config/aarch64/aarch64.c   |   23 +++++++++++++++++++++++
>>   gcc/config/aarch64/aarch64.h   |   13 ++++++++-----
>>   gcc/config/aarch64/aarch64.opt |    4 ++++
>>   3 files changed, 35 insertions(+), 5 deletions(-)
>>
>> diff --git a/gcc/config/aarch64/aarch64.c b/gcc/config/aarch64/aarch64.c
>> index 752df4e..c70b161 100644
>> --- a/gcc/config/aarch64/aarch64.c
>> +++ b/gcc/config/aarch64/aarch64.c
>> @@ -440,6 +440,17 @@ aarch64_is_long_call_p (rtx sym)
>>     return aarch64_decl_is_long_call_p (SYMBOL_REF_DECL (sym));
>>   }
>>
>> +void
>> +aarch64_function_profiler (FILE *file, int labelno ATTRIBUTE_UNUSED)
>> +{
>> +    if (flag_fentry)
>> +    {
>> +        fprintf (file, "\tmov\tx9, x30\n");
>> +        fprintf (file, "\tbl\t__fentry__\n");
>> +        fprintf (file, "\tmov\tx30, x9\n");
>> +    }
>> +}
>> +
> 
> you can even omit the mov x30,x9 at the call site if
> __fentry__ does
> 
>   stp x9,x30,[sp,#-16]!
>   //... profiling
>   ldp x30,x9,[sp],#16
>   ret x9
> 
> is there a problem with this?
> 

__fentry__ is responsible to protect all registers.

> i think the rest of the patch means that -pg retains
> the old behaviour and -pg -mfentry emits this new entry.
> 
> note that -pg rejects -fomit-frame-pointer (for no good
> reason), that should be fixed separately (it seems the
> kernel now relies on frame pointers on aarch64, but the
> mcount abi does not require this and e.g. the glibc
> mcount does not use it.)
>

Yes, kernel configuration CONFIG_FRAME_POINTER is forced on arm64,
that the kernel is compiled without -fomit-frame-pointer.

Thanks,

Li Bin

>>   /* Return true if the offsets to a zero/sign-extract operation
>>      represent an expression that matches an extend operation.  The
>>      operands represent the paramters from
>> @@ -7414,6 +7425,15 @@ aarch64_emit_unlikely_jump (rtx insn)
>>     add_int_reg_note (insn, REG_BR_PROB, very_unlikely);
>>   }
>>
>> +/* Return true, if profiling code should be emitted before
>> + * prologue. Otherwise it returns false.
>> + * Note: For x86 with "hotfix" it is sorried.  */
>> +static bool
>> +aarch64_profile_before_prologue (void)
>> +{
>> +    return flag_fentry != 0;
>> +}
>> +
>>   /* Expand a compare and swap pattern.  */
>>
>>   void
>> @@ -8454,6 +8474,9 @@ aarch64_cannot_change_mode_class (enum machine_mode from,
>>   #undef TARGET_ASM_ALIGNED_SI_OP
>>   #define TARGET_ASM_ALIGNED_SI_OP "\t.word\t"
>>
>> +#undef TARGET_PROFILE_BEFORE_PROLOGUE
>> +#define TARGET_PROFILE_BEFORE_PROLOGUE aarch64_profile_before_prologue
>> +
>>   #undef TARGET_ASM_CAN_OUTPUT_MI_THUNK
>>   #define TARGET_ASM_CAN_OUTPUT_MI_THUNK \
>>     hook_bool_const_tree_hwi_hwi_const_tree_true
>> diff --git a/gcc/config/aarch64/aarch64.h b/gcc/config/aarch64/aarch64.h
>> index 77b2bb9..65e34fc 100644
>> --- a/gcc/config/aarch64/aarch64.h
>> +++ b/gcc/config/aarch64/aarch64.h
>> @@ -804,13 +804,16 @@ do {                                         \
>>   #define PROFILE_HOOK(LABEL)                        \
>>     {                                    \
>>       rtx fun, lr;                            \
>> -    lr = get_hard_reg_initial_val (Pmode, LR_REGNUM);            \
>> -    fun = gen_rtx_SYMBOL_REF (Pmode, MCOUNT_NAME);            \
>> -    emit_library_call (fun, LCT_NORMAL, VOIDmode, 1, lr, Pmode);    \
>> +    if (!flag_fentry)
>> +      {
>> +        lr = get_hard_reg_initial_val (Pmode, LR_REGNUM);            \
>> +        fun = gen_rtx_SYMBOL_REF (Pmode, MCOUNT_NAME);            \
>> +        emit_library_call (fun, LCT_NORMAL, VOIDmode, 1, lr, Pmode);    \
>> +      }
>>     }
>>
>> -/* All the work done in PROFILE_HOOK, but still required.  */
>> -#define FUNCTION_PROFILER(STREAM, LABELNO) do { } while (0)
>> +#define FUNCTION_PROFILER(STREAM, LABELNO)
>> +    aarch64_function_profiler(STREAM, LABELNO)
>>
>>   /* For some reason, the Linux headers think they know how to define
>>      these macros.  They don't!!!  */
>> diff --git a/gcc/config/aarch64/aarch64.opt b/gcc/config/aarch64/aarch64.opt
>> index 266d873..9e4b408 100644
>> --- a/gcc/config/aarch64/aarch64.opt
>> +++ b/gcc/config/aarch64/aarch64.opt
>> @@ -124,3 +124,7 @@ Enum(aarch64_abi) String(ilp32) Value(AARCH64_ABI_ILP32)
>>
>>   EnumValue
>>   Enum(aarch64_abi) String(lp64) Value(AARCH64_ABI_LP64)
>> +
>> +mfentry
>> +Target Report Var(flag_fentry) Init(0)
>> +Emit profiling counter call at function entry immediately after prologue.
>>
> 
> 
> .
>