Re: [PATCH v6 8/8] linux-user: Load pie executables at upper memory

[Richard Henderson <richard.henderson@linaro.org>]

On 8/1/23 16:27, Helge Deller wrote:
> +/* where to map binaries? */
> +#if HOST_LONG_BITS == 64 && TARGET_ABI_BITS == 64
> +# define TASK_UNMAPPED_BASE_PIE 0x5500000000
> +# define TASK_UNMAPPED_BASE	0x7000000000
> +#elif HOST_LONG_BITS == 64 && TARGET_ABI_BITS == 32
> +# define TASK_UNMAPPED_BASE_PIE	0x00300000
> +# define TASK_UNMAPPED_BASE	(GUEST_ADDR_MAX - 0x20000000 + 1)
> +#else /* HOST_LONG_BITS == 32 && TARGET_ABI_BITS == 32 */
> +# define TASK_UNMAPPED_BASE_PIE	0x00000000
> +# define TASK_UNMAPPED_BASE	0x40000000
> +#endif

It would probably be easier to follow if you use the kernel's name: ELF_ET_DYN_BASE. 
Should be in linux-user/$GUEST/target_mmap.h with TASK_UNMAPPED_BASE, per my comment vs 
patch 7.


> +        /* do sanity checks on guest memory layout */
> +        if (mmap_next_start >= GUEST_ADDR_MAX) {
> +            mmap_next_start = GUEST_ADDR_MAX - 0x1000000000 + 1;
> +        }

What in the world is that random number?  It certainly won't compile on 32-bit host, and 
certainly isn't relevant to a 32-bit guest.

> +        if (TASK_UNMAPPED_BASE_PIE >= mmap_next_start) {
> +            fprintf(stderr, "Memory too small for PIE executables.\n");
> +            exit(EXIT_FAILURE);
> +        }

Really bad timing for this diagnostic.  What if a PIE executable isn't even being used?

Both TASK_UNMAPPED_BASE and ELF_ET_DYN_BASE could be computed in main (or a subroutine), 
when reserved_va is assigned.


r~