Re: [Patch] gcn: Add __builtin_gcn_{get_stack_limit,first_call_this_thread_p}

[Andrew Stubbs <ams@codesourcery.com>]

On 18/11/2022 17:20, Tobias Burnus wrote:
> This patch adds two builtins (getting end-of-stack pointer and
> a Boolean answer whether it was the first call to the builtin on this 
> thread).
> 
> The idea is to replace some hard-coded values in newlib, permitting to move
> later to a manually allocated stack on the compiler side without the 
> need to
> modify newlib again. The GCC patch matches what newlib did in reent; I 
> could
> imagine that we change this later on.
> 
> Lightly tested (especially by visual inspection).
> Currently doing a final regtest, OK when it passes?
> 
> Any  comments to this patch - or the attached newlib patch?*
> 
> Tobias
> 
> (*) I also included a patch to newlib to see where were are heading
> + to actually use them for regtesting ...

This looks wrong:

> +	/* stackbase = (stack_segment_decr & 0x0000ffffffffffff)
> +			+ stack_wave_offset);
> +	   seg_size = dispatch_ptr->private_segment_size;
> +	   stacklimit = stackbase + seg_size*64;
> +	   with segsize = dispatch_ptr + 6*sizeof(int16_t) + 3*sizeof(int32_t);
> +	   cf. struct hsa_kernel_dispatch_packet_s in the HSA doc.  */
> +	rtx ptr;
> +	if (cfun->machine->args.reg[DISPATCH_PTR_ARG] >= 0
> +	    && cfun->machine->args.reg[PRIVATE_SEGMENT_BUFFER_ARG] >= 0)
> +	  {
> +	    rtx size_rtx = gen_rtx_REG (DImode,
> +					cfun->machine->args.reg[DISPATCH_PTR_ARG]);
> +	    size_rtx = gen_rtx_MEM (DImode,
> +				    gen_rtx_PLUS (DImode, size_rtx,
> +						  GEN_INT (6*16 + 3*32)));
> +	    size_rtx = gen_rtx_MULT (DImode, size_rtx, GEN_INT (64));
> +

seg_size is calculated from the private_segment_size loaded from the 
dispatch_ptr, not calculated from the dispatch_ptr itself.

Andrew