Re: [PATCH 4/8] Implement target_emit_ops

[Antoine Tremblay <antoine.tremblay@ericsson.com>]

On 09/18/2015 08:43 AM, Yao Qi wrote:
> From: Pierre Langlois <pierre.langlois@arm.com>
>
> This patch implements compiling agent expressions to native code for
> AArch64.  This allows us to compile conditions set on fast tracepoints.
>
> The compiled function has the following prologue:
>
> High *------------------------------------------------------*
>       | LR                                                   |
>       | FP                                                   | <- FP
>       | x1  (ULONGEST *value)                                |
>       | x0  (unsigned char *regs)                            |
> Low  *------------------------------------------------------*
>
> We save the function's argument on the stack as well as the return
> address and the frame pointer.  We then set the current frame pointer to
> point to the previous one.
>
> The generated code for the expression will freely update the stack
> pointer so we use the frame pointer to refer to `*value' and `*regs'.
> `*value' needs to be accessed in the epilogue of the function, in order
> to set it to whatever is on top of the stack.  `*regs' needs to be passed
> down to the `gdb_agent_get_reg' function with the `reg' operation.
>
> +static void
> +aarch64_emit_prologue (void)
> +{
> +  uint32_t buf[16];
> +  uint32_t *p = buf;
> +
> +  /* This function emit a prologue for the following function prototype:
> +
> +     e
....

Hi,
   I'm working on adding JIT compiling of agent expressions for ARM and 
I've been looking at the aarch64 implementation.

   I'm wondering is there a reason we don't use gcc to generate the 
native bytecode like done on x86 ?

x86 has a macro like so :

#define EMIT_ASM(NAME, INSNS)						
   do									
     {									
       extern unsigned char start_ ## NAME, end_ ## NAME;		
       add_insns (&start_ ## NAME, &end_ ## NAME - &start_ ## NAME);	
       __asm__ ("jmp end_" #NAME "\n"					
	       "\t" "start_" #NAME ":"					
	       "\t" INSNS "\n"						
	       "\t" "end_" #NAME ":");					
     } while (0)

Could the same be done for armv7 or there's a reason that prevents it ?

Same question for aarch64 ?

Thanks,
Antoine