Re: [PATCH for-8.1] linux-user: Define real MAP_FIXED_NOREPLACE value

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

On 8/8/23 04:52, Akihiko Odaki wrote:
> do_brk() assumes target_mmap() emulates MAP_FIXED_NOREPLACE even when
> the host does not support it. However, such emulation is not possible
> if MAP_FIXED_NOREPLACE is defined as zero.
> 
> Define MAP_FIXED_NOREPLACE with the real value instead of zero if it is
> not defined.
> 
> Fixes: e69e032d1a ("linux-user: Use MAP_FIXED_NOREPLACE for do_brk()")
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> ---
>   include/qemu/osdep.h | 8 ++++++--
>   linux-user/elfload.c | 1 -
>   2 files changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
> index cc61b00ba9..1aac17ec2f 100644
> --- a/include/qemu/osdep.h
> +++ b/include/qemu/osdep.h
> @@ -289,8 +289,12 @@ void QEMU_ERROR("code path is reachable")
>   #ifndef MAP_ANONYMOUS
>   #define MAP_ANONYMOUS MAP_ANON
>   #endif
> -#ifndef MAP_FIXED_NOREPLACE
> -#define MAP_FIXED_NOREPLACE 0
> +#if defined(__linux__) && !defined(MAP_FIXED_NOREPLACE)
> +#if HOST_ALPHA

HOST_ALPHA is not a thing.  Also, see

https://lore.kernel.org/qemu-devel/20230808120303.585509-3-pbonzini@redhat.com/

where host support for Alpha is completely removed.


> +#define MAP_FIXED_NOREPLACE 0x200000
> +#else
> +#define MAP_FIXED_NOREPLACE 0x100000
> +#endif

Which supported hosts do not define this value?  Can we simply remove the fallback?


r~