Re: [PATCH v7 13/14] linux-user: Adjust initial brk when interpreter is close to executable

[Helge Deller]

Hi Richard,

Thanks for putting this all together!
I'll test asap.

I haven't checked yet, but Akihiko did send a revised v2 patch
series, while my v6 series included his older v1 patches.
We should consider his latest series...

One other thing below....

On 8/3/23 03:53, Richard Henderson wrote:
> From: Helge Deller <deller@gmx.de>
>
> While we attempt to load a ET_DYN executable far away from
> TASK_UNMAPPED_BASE, we are not completely in control of the
> address space layout.  If the interpreter lands close to
> the executable, leaving insufficient heap space, move brk.
>
> Signed-off-by: Helge Deller <deller@gmx.de>
> [rth: Re-order after ELF_ET_DYN_BASE patch so that we do not
>   "temporarily break" tsan, and also to minimize the changes required.
>   Remove image_info.reserve_brk as unused.]
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>   linux-user/qemu.h    |  1 -
>   linux-user/elfload.c | 51 +++++++++++++-------------------------------
>   2 files changed, 15 insertions(+), 37 deletions(-)
> ...
> @@ -3229,7 +3208,8 @@ static void load_elf_image(const char *image_name, int 
> image_fd,
>       info->end_code = 0;
>       info->start_data = -1;
>       info->end_data = 0;
> -    info->brk = 0;
> +    /* Usual start for brk is after all sections of the main executable. */
> +    info->brk = TARGET_PAGE_ALIGN(hiaddr);

This is from my original patch, and is probably wrong.
I think this needs to be:
    info->brk = HOST_PAGE_ALIGN(hiaddr);

The brk page needs to be aligned to the host page size variable (which
is always >= target page size).
The page will be mapped +rw (on host), so may need the distance to code/shared
libs below it, and for that distance target-alignment may not be sufficient.

I think this fixes the problem which joel faced with armel static binary
on ppc64le.

Helge