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Date: Sun, 13 Sep 2020 09:11:23 -0500
From: Segher Boessenkool <segher@kernel.crashing.org>
To: William Tambe <tambewilliam@gmail.com>
Cc: gcc-help@gcc.gnu.org
Subject: Re: Unconditional trap
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Hi!

On Sat, Sep 12, 2020 at 03:17:03PM -0500, William Tambe via Gcc-help wrote:
> I am currently using following for trap instruction:
> 
> (define_insn "trap"
>   [(trap_if (const_int 1) (const_int 0))]
>   ""
>   "brk")

This looks fine.

> However it causes the compiler to generate a trap when address 0 is
> used; in the example below, I have a function that prints characters
> through the UART using address 0; but the resulting assembly generates
> a function that traps instead.
> 
> #define UART_ADDR 0
> void uart_print (char *s) {
>         while (*s) {
>                 *(volatile char *)UART_ADDR = *s;
>                 ++s;
>         }
> }
> 
> How can one implement unconditional trap ?

You should implement TARGET_ADDR_SPACE_ZERO_ADDRESS_VALID to make 0 a
valid address.


Segher