Re: [PATCH] rs6000: Stackoverflow in optimized code on PPC (PR100799)

[Jakub Jelinek <jakub@redhat.com>]

On Fri, Mar 22, 2024 at 01:00:21PM +0530, Ajit Agarwal wrote:
> When using FlexiBLAS with OpenBLAS we noticed corruption of
> the parameters passed to OpenBLAS functions. FlexiBLAS
> basically provides a BLAS interface where each function
> is a stub that forwards the arguments to a real BLAS lib,
> like OpenBLAS.
> 
> Fixes the corruption of caller frame checking number of
> arguments is less than equal to GP_ARG_NUM_REG (8)
> excluding hidden unused DECLS.

Thanks for working on this.

> 2024-03-22  Ajit Kumar Agarwal  <aagarwa1@linux.ibm.com>
> 
> gcc/ChangeLog:
> 
>         PR rtk-optimization/100799
>         * config/rs600/rs600-calls.cc (rs6000_function_arg): Don't

These 2 lines are 8 space indented rather than tab.

> 	generate parameter save area if number of arguments passed
> 	less than equal to GP_ARG_NUM_REG (8) excluding hidden
> 	paramter.
> 	* function.cc (assign_parms_initialize_all): Check for hidden
> 	parameter in fortran code and set the flag hidden_string_length
> 	and actual paramter passed excluding hidden unused DECLS.

s/paramter/parameter/

> 	* function.h: Add new field hidden_string_length and
> 	actual_parm_length in function structure.

Why do you need to change generic code for something that will only be
used by a single target?
I mean, why don't you add the extra members in rs6000.h (struct rs6000_args)
and initialize them in rs6000-call.cc (init_cumulative_args) -
the function.cc function you've modified is the only one which uses
INIT_CUMULATIVE_INCOMING_ARGS and in that case init_cumulative_args is
called with incoming == true, so move the stuff from function.cc there.

> --- a/gcc/config/rs6000/rs6000-call.cc
> +++ b/gcc/config/rs6000/rs6000-call.cc
> @@ -1857,7 +1857,16 @@ rs6000_function_arg (cumulative_args_t cum_v, const function_arg_info &arg)
>  
>  	  return rs6000_finish_function_arg (mode, rvec, k);
>  	}
> -      else if (align_words < GP_ARG_NUM_REG)
> +     /* Workaround buggy C/C++ wrappers around Fortran routines with
> +	character(len=constant) arguments if the hidden string length arguments
> +	are passed on the stack; if the callers forget to pass those arguments,
> +	attempting to tail call in such routines leads to stack corruption.
> +	Avoid return stack space for parameters <= 8 excluding hidden string
> +	length argument is passed (partially or fully) on the stack in the
> +	caller and the callee needs to pass any arguments on the stack.  */
> +      else if (align_words < GP_ARG_NUM_REG
> +	       || (cfun->hidden_string_length
> +	       && cfun->actual_parm_length <= GP_ARG_NUM_REG))
>  	{
>  	  if (TARGET_32BIT && TARGET_POWERPC64)
>  	    return rs6000_mixed_function_arg (mode, type, align_words);
> diff --git a/gcc/function.cc b/gcc/function.cc
> index 3cef6c17bce..1318564b466 100644
> --- a/gcc/function.cc
> +++ b/gcc/function.cc
> @@ -2326,6 +2326,32 @@ assign_parms_initialize_all (struct assign_parm_data_all *all)
>  #endif
>    all->args_so_far = pack_cumulative_args (&all->args_so_far_v);
>  
> +  unsigned int num_args = 0;
> +  unsigned int hidden_length = 0;
> +
> +  /* Workaround buggy C/C++ wrappers around Fortran routines with
> +     character(len=constant) arguments if the hidden string length arguments
> +     are passed on the stack; if the callers forget to pass those arguments,
> +     attempting to tail call in such routines leads to stack corruption.
> +     Avoid return stack space for parameters <= 8 excluding hidden string
> +     length argument is passed (partially or fully) on the stack in the
> +     caller and the callee needs to pass any arguments on the stack.  */
> +  for (tree arg = DECL_ARGUMENTS (current_function_decl);
> +       arg; arg = DECL_CHAIN (arg))
> +    {
> +      num_args++;
> +      if (DECL_HIDDEN_STRING_LENGTH (arg))
> +	{
> +	  tree parmdef = ssa_default_def (cfun, arg);
> +	  if (parmdef == NULL || has_zero_uses (parmdef))
> +	    {
> +	      cfun->hidden_string_length = 1;
> +	      hidden_length++;
> +	    }
> +	}
> +   }
> +
> +  cfun->actual_parm_length = num_args - hidden_length;
>  #ifdef INCOMING_REG_PARM_STACK_SPACE
>    all->reg_parm_stack_space
>      = INCOMING_REG_PARM_STACK_SPACE (current_function_decl);
> diff --git a/gcc/function.h b/gcc/function.h
> index 19e15bd63b0..5984f0007c2 100644
> --- a/gcc/function.h
> +++ b/gcc/function.h
> @@ -346,6 +346,11 @@ struct GTY(()) function {
>    /* Last assigned dependence info clique.  */
>    unsigned short last_clique;
>  
> +  /* Actual parameter length ignoring hidden paramter.
> +     This is done to C++ wrapper calling fortran module
> +     which has hidden parameter that are not used.  */
> +  unsigned int actual_parm_length;
> +
>    /* Collected bit flags.  */
>  
>    /* Number of units of general registers that need saving in stdarg
> @@ -442,6 +447,11 @@ struct GTY(()) function {
>    /* Set for artificial function created for [[assume (cond)]].
>       These should be GIMPLE optimized, but not expanded to RTL.  */
>    unsigned int assume_function : 1;
> +
> +  /* Hidden parameters while calling C++ wrapper to fortran
> +     module. Set if there is hidden parameter in fortran
> +     module while called C++ wrapper.  */
> +  unsigned int hidden_string_length : 1;
>  };
>  
>  /* Add the decl D to the local_decls list of FUN.  */
> -- 
> 2.39.3

	Jakub