Re: [Qemu-devel] [PATCH 1/3] configure: Disable W^X on OpenBSD

[Thomas Huth]

On 2019-01-25 20:27, Philippe Mathieu-Daudé wrote:
> Since OpenBSD 6.0 [1], W^X is enforced by default [2].
> TCG requires WX access. Disable W^X if it is available.
> This fixes:
> 
>   # lm32-softmmu/qemu-system-lm32
>   Could not allocate dynamic translator buffer
> 
>   # sysctl kern.wxabort=1
>   kern.wxabort: 0 -> 1
>   # lm32-softmmu/qemu-system-lm32
>   mmap: Not supported
>   Abort trap (core dumped)
>   # gdb -q lm32-softmmu/qemu-system-lm32 qemu-system-lm32.core
>   (gdb) bt
>   #0  0x000017e3c156c50a in _thread_sys___syscall () at {standard input}:5
>   #1  0x000017e3c15e5d7a in *_libc_mmap (addr=Variable "addr" is not 
> available.) at /usr/src/lib/libc/sys/mmap.c:47
>   #2  0x000017e17d9abc8b in alloc_code_gen_buffer () at 
> /usr/src/qemu/accel/tcg/translate-all.c:1064
>   #3  0x000017e17d9abd04 in code_gen_alloc (tb_size=0) at 
> /usr/src/qemu/accel/tcg/translate-all.c:1112
>   #4  0x000017e17d9abe81 in tcg_exec_init (tb_size=0) at 
> /usr/src/qemu/accel/tcg/translate-all.c:1149
>   #5  0x000017e17d9897e9 in tcg_init (ms=0x17e45e456800) at 
> /usr/src/qemu/accel/tcg/tcg-all.c:66
>   #6  0x000017e17d9891b8 in accel_init_machine (acc=0x17e3c3f50800, 
> ms=0x17e45e456800) at /usr/src/qemu/accel/accel.c:63
>   #7  0x000017e17d989312 in configure_accelerator (ms=0x17e45e456800, 
> progname=0x7f7fffff07b0 "lm32-softmmu/qemu-system-lm32") at 
> /usr/src/qemu/accel/accel.c:111
>   #8  0x000017e17d9d8616 in main (argc=1, argv=0x7f7fffff06b8, 
> envp=0x7f7fffff06c8) at vl.c:4325
> 
> [1] https://www.openbsd.org/faq/upgrade60.html
> [2] https://undeadly.org/cgi?action=article&sid=20160527203200
> 
> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
> ---
>  configure | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/configure b/configure
> index b18281c61f..f6acc028a7 100755
> --- a/configure
> +++ b/configure
> @@ -5795,6 +5795,17 @@ if test "$mingw32" = "yes" ; then
>      done
>  fi
>  
> +# Disable W^X if available

I'd like to suggest to mention OpenBSD in the comment.

> +if test "$tcg" = "yes" -a "$targetos" = "OpenBSD"; then
> +    cat > $TMPC <<EOF
> +    int main(void) { return 0; }
> +EOF
> +    wx_ldflags="-Wl,-z,wxneeded"
> +    if compile_prog "" "$wx_ldflags"; then
> +        QEMU_LDFLAGS="$QEMU_LDFLAGS -Wl,-z,wxneeded"

Why do you introduce the wx_ldflags variable above, just to use it one
time? I'd suggest to either use it in the QEMU_LDFLAGS line, too, or to
get rid of the variable completely and always use -Wl,-z,wxneeded directly.

 Thomas

> +    fi
> +fi
> +
>  qemu_confdir=$sysconfdir$confsuffix
>  qemu_moddir=$libdir$confsuffix
>  qemu_datadir=$datadir$confsuffix