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

[Philippe Mathieu-Daudé]

On 1/28/19 9:43 AM, Thomas Huth wrote:
> 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.

Good idea.

>> +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.

I did not notice :) I'll remove the variable to avoid creating variables
used once.

Thanks!

Phil.

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