Re: [Qemu-devel] [PATCH v2] Fix QEMU build on OpenBSD on x86 archs

[Stefan Weil <sw@weilnetz.de>]

Am 10.12.2013 08:48, schrieb Brad Smith:
> On 10/12/13 2:07 AM, Stefan Weil wrote:
>> Am 10.12.2013 02:26, schrieb Brad Smith:
>>> This resolves the build issue with building the ROMs on OpenBSD on
>>> x86 archs.
>>> As of OpenBSD 5.3 the compiler builds PIE binaries by default and
>>> thus the
>>> whole OS/packages and so forth. The ROMs need to have PIE disabled.
>>> This
>>> is my initial attempt at trying to get somehting upstream so that QEMU
>>> both builds out of the box and to resolve the build issue with the
>>> buildbots that has been around for awhile. We have a patch in our ports
>>> tree but it is just the flags hardcoded into the Makefile which
>>> obviously
>>> is not appropriate for upstream.
>>>
>>>  From the OpenBSD buildbots..
>>>    Building optionrom/multiboot.img
>>> ld: multiboot.o: relocation R_X86_64_16 can not be used when making
>>> a shared object; recompile with -fPIC
>>>
>>>
>>> Signed-off by: Brad Smith <brad@comstyle.com>
>>> ---
>>>
>>> Changes in v2:
>>>      * Fix '==' is not portable syntax.
>>>
>>>
>>> diff --git a/configure b/configure
>>> index 508f6a5..6d84885 100755
>>> --- a/configure
>>> +++ b/configure
>>> @@ -1342,6 +1342,10 @@ EOF
>>>     if compile_prog "-fPIE -DPIE" "-pie"; then
>>>       QEMU_CFLAGS="-fPIE -DPIE $QEMU_CFLAGS"
>>>       LDFLAGS="-pie $LDFLAGS"
>>> +    if test "$targetos" = OpenBSD; then
>>> +      CC_NOPIE="-fno-pie"
>>> +      LD_NOPIE="-nopie"
>>> +    fi
>>>       pie="yes"
>>>       if compile_prog "" "-Wl,-z,relro -Wl,-z,now" ; then
>>>         LDFLAGS="-Wl,-z,relro -Wl,-z,now $LDFLAGS"
>>> @@ -4307,6 +4311,8 @@ if test "$gcov" = "yes" ; then
>>>     echo "CONFIG_GCOV=y" >> $config_host_mak
>>>     echo "GCOV=$gcov_tool" >> $config_host_mak
>>>   fi
>>> +echo "CC_NOPIE=$CC_NOPIE" >> $config_host_mak
>>> +echo "LD_NOPIE=$LD_NOPIE" >> $config_host_mak
>>>
>>>   # use included Linux headers
>>>   if test "$linux" = "yes" ; then
>>> diff --git a/pc-bios/optionrom/Makefile b/pc-bios/optionrom/Makefile
>>> index 57d8bd0..0b35000 100644
>>> --- a/pc-bios/optionrom/Makefile
>>> +++ b/pc-bios/optionrom/Makefile
>>> @@ -12,6 +12,7 @@ $(call set-vpath, $(SRC_PATH)/pc-bios/optionrom)
>>>   CFLAGS := -Wall -Wstrict-prototypes -Werror -fomit-frame-pointer
>>> -fno-builtin
>>>   CFLAGS += -I$(SRC_PATH)
>>>   CFLAGS += $(call cc-option, $(CFLAGS), -fno-stack-protector)
>>> +CFLAGS += $(CC_NOPIE)
>>
>> Would it be possible to add -fno-pie unconditionally here ...
>>
>>
>>>   QEMU_CFLAGS = $(CFLAGS)
>>>
>>>   build-all: multiboot.bin linuxboot.bin kvmvapic.bin
>>> @@ -20,7 +21,7 @@ build-all: multiboot.bin linuxboot.bin kvmvapic.bin
>>>   .SECONDARY:
>>>
>>>   %.img: %.o
>>> -    $(call quiet-command,$(LD) -Ttext 0 -e _start -s -o $@ $<," 
>>> Building $(TARGET_DIR)$@")
>>> +    $(call quiet-command,$(LD) $(LD_NOPIE) -Ttext 0 -e _start -s -o
>>> $@ $<,"  Building $(TARGET_DIR)$@")
>>>
>>
>>
>> ... and use -nopie here? I tried it in my Linux build environment, and
>> it seems to work.
>>
>> Then no changes to file configure are needed.
>
> The linker flag definitely does not exist everywhere so that would
> break the build on other OS/toolchain combinations; for example stock
> binutils does not have this flag. I would not have bothered going this
> route if I didn't see having the flags hard coded as causing a problem.
>


Thank you for your explanation. I cc your patch to qemu-stable because
fixing QEMU 1.7 for OpenBSD might be a good idea, too.

Reviewed-by: Stefan Weil <sw@weilnetz.de>


If other hosts beside OpenBSD will need thismodification in the future,
I suggest modified code like this:

    if compile_prog "-fPIE -DPIE" "-pie"; then
      QEMU_CFLAGS="-fPIE -DPIE $QEMU_CFLAGS"
      LDFLAGS="-pie $LDFLAGS"
      # [...]
    fi

    if compile_prog "-fno-pie" "-nopie"; then
      CFLAGS_NOPIE="-fno-pie"
      LDFLAGS_NOPIE="-nopie"
    fi

(separate if blocks in configure and use CFLAGS_NOPIE, LDFLAGS_NOPIE
instead of CC_NOPIE, LD_NOPIE, this also needs a modified Makefile).

Regards,
Stefan