Re: [Qemu-devel] [PATCH] target-i386: Enhance the stub for kvm_arch_get_supported_cpuid()

[Kamil Rytarowski]

Ping, still valid.

On 15.02.2019 00:38, Kamil Rytarowski wrote:
> On 14.02.2019 21:51, Paolo Bonzini wrote:
>> On 14/02/19 20:41, Kamil Rytarowski wrote:
>>> Please do replace the current kludge that is sensitive to:
>>>  - compiler behavior that can change with new versions
>>>  - compiler gcc/clang
>>>  - optimization options
>>
>> Not really, any half-decent compiler will optimize away "if (0)" and
>> QEMU is far from being the only software that relies on that.
>>
>> GCC has been doing that even at -O0 for like 15 years, at some point it
>> was basically the only optimization it did.  Just try it for yourself:
>>
>>      int f(void);
>>
>>      int main()
>>      {
>>              if (0)
>>                      return f();
>>              else
>>                      return 0;
>>      }
>>
>> Throw it at all compilers and optimization levels, and it *will* work.
>> If it doesn't then I'll consider again your patch.
>>
> 
> I consider it as fragile hack and certainly not something to depend on.
> Also in some circumstances of such code, especially "if (zero0)" we want
> to enable disabled code under a debugger.
> 
> There were also kernel backdoors due to this optimization.
> 
>>>  - linux(KVM) - non-linux (no-KVM) build
>>
>> That's the point.  We want your non-Linux non-KVM build to be as lean as
>> possible and not cause possible run-time failures due to people
>> forgetting about them.
>>
>>>  - community not actively testing non-linux no-kvm build with
>>> optimization on clang
>>
>> False, we test OS X and there are VM builds for the BSDs.
> 
> Unfortunately not in the same combination of options as nobody caught it
> in years. (Probably not many people actually develop it on these OSes
> with debug flags). I was keeping this patch locally for some time now.
> This hack was introduced several years ago.
> 
>>> My patch replaced it makes it work.
>>>
>>> Build error:
>>>
>>>   LINK    i386-bsd-user/qemu-i386
>>
>> Ok, please use "make -C i386-bsd-user target/i386/cpu.o V=1" to get the
>> command line, invoke it again with "-save-temps" at the end, and send me
>> both the command line and the resulting "cpu.i" file.
>>
> 
> I'm building qemu with pkgsrc that provides all the dependencies and
> compiler settings. It also uses wrappers to translate original compiler
> options with transformed ones.
> 
> Log from pkgsrc with command lines:
> 
> http://netbsd.org/~kamil/qemu/qemu-build-2019-02-14.txt.bz2
> 
> Requested cpu.i (hopefully correctly generated)
> 
> http://netbsd.org/~kamil/qemu/cpu.i.bz2
> 
> I've generated it manually with this command.
> 
> /usr/local/bin/clang -iquote
> /tmp/pkgsrc-tmp/wip/qemu-haxm/work/qemu-3.0.0/target/i386 -iquote
> target/i386 -iquote /tmp/pkgsrc-tmp/wip/qemu-haxm/work/qemu-3.0.0/tcg
> -iquote /tmp/pkgsrc-tmp/wip/qemu-haxm/work/qemu-3.0.0/tcg/i386 -iquote .
> -iquote /tmp/pkgsrc-tmp/wip/qemu-haxm/work/qemu-3.0.0 -iquote
> /tmp/pkgsrc-tmp/wip/qemu-haxm/work/qemu-3.0.0/accel/tcg -iquote
> /tmp/pkgsrc-tmp/wip/qemu-haxm/work/qemu-3.0.0/include
> -I/tmp/pkgsrc-tmp/wip/qemu-haxm/work/.x11-buildlink/include/pixman-1
> -I/tmp/pkgsrc-tmp/wip/qemu-haxm/work/qemu-3.0.0/dtc/libfdt -pthread
> -I/tmp/pkgsrc-tmp/wip/qemu-haxm/work/.buildlink/include/glib/glib-2.0
> -I/tmp/pkgsrc-tmp/wip/qemu-haxm/work/.buildlink/lib/glib-2.0/include
> -I/tmp/pkgsrc-tmp/wip/qemu-haxm/work/.buildlink/include -m64 -mcx16
> -D_GNU_SOURCE -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE
> -Wstrict-prototypes -Wredundant-decls -Wall -Wundef -Wwrite-strings
> -Wmissing-prototypes -fno-strict-aliasing -fno-common -fwrapv
> -Wno-error=address-of-packed-member -Wno-string-plus-int
> -Wno-initializer-overrides -Wexpansion-to-defined -Wendif-labels
> -Wno-shift-negative-value -Wno-missing-include-dirs -Wempty-body
> -Wnested-externs -Wformat-security -Wformat-y2k -Winit-self
> -Wignored-qualifiers -Wold-style-definition -Wtype-limits
> -fstack-protector-strong
> -I/tmp/pkgsrc-tmp/wip/qemu-haxm/work/.buildlink/include/libpng16
> -I/tmp/pkgsrc-tmp/wip/qemu-haxm/work/qemu-3.0.0/capstone/include -iquote
> .. -iquote /tmp/pkgsrc-tmp/wip/qemu-haxm/work/qemu-3.0.0/target/i386
> -DNEED_CPU_H -iquote
> /tmp/pkgsrc-tmp/wip/qemu-haxm/work/qemu-3.0.0/include -MMD -MP -MT
> target/i386/cpu.o -MF target/i386/cpu.d -O2 -g -O2 -O0 -g -ggdb
> -I/tmp/pkgsrc-tmp/wip/qemu-haxm/work/.buildlink/include/SDL2
> -I/tmp/pkgsrc-tmp/wip/qemu-haxm/work/.x11-buildlink/include
> -I/tmp/pkgsrc-tmp/wip/qemu-haxm/work/.x11-buildlink/include/libdrm
> -I/tmp/pkgsrc-tmp/wip/qemu-haxm/work/.buildlink/include/glib/gio-unix-2.0
> -I/usr/include/krb5 -c -o target/i386/cpu.o
> /tmp/pkgsrc-tmp/wip/qemu-haxm/work/qemu-3.0.0/target/i386/cpu.c
> -Qunused-arguments -fstack-protector -save-temps
> 
>> Paolo
>>
>>> /usr/bin/ld: /usr/lib/libc.so and /usr/lib/crt0.o: warning: multiple
>>> common of `environ'
>>> /usr/bin/ld: target/i386/cpu.o: in function `x86_cpu_filter_features':
>>> /tmp/pkgsrc-tmp/emulators/qemu/work/qemu-3.1.0/target/i386/cpu.c:5047:
>>> undefined reference to `kvm_arch_get_supported_cpuid'
>>> /usr/bin/ld:
>>> /tmp/pkgsrc-tmp/emulators/qemu/work/qemu-3.1.0/target/i386/cpu.c:5048:
>>> undefined reference to `kvm_arch_get_supported_cpuid'
>>> /usr/bin/ld:
>>> /tmp/pkgsrc-tmp/emulators/qemu/work/qemu-3.1.0/target/i386/cpu.c:5049:
>>> undefined reference to `kvm_arch_get_supported_cpuid'
>>> /usr/bin/ld:
>>> /tmp/pkgsrc-tmp/emulators/qemu/work/qemu-3.1.0/target/i386/cpu.c:5050:
>>> undefined reference to `kvm_arch_get_supported_cpuid'
>>> /usr/bin/ld:
>>> /tmp/pkgsrc-tmp/emulators/qemu/work/qemu-3.1.0/target/i386/cpu.c:5051:
>>> undefined reference to `kvm_arch_get_supported_cpuid'
>>> clang-9: error: linker command failed with exit code 1 (use -v to see
>>> invocation)
>>> make[1]: *** [Makefile:199: qemu-i386] Error 1
>>> gmake: *** [Makefile:483: subdir-i386-bsd-user] Error 2
>>> gmake: *** Waiting for unfinished jobs....
>>>   LINK    x86_64-bsd-user/qemu-x86_64
>>> /usr/bin/ld: /usr/lib/libc.so and /usr/lib/crt0.o: warning: multiple
>>> common of `environ'
>>> /usr/bin/ld: target/i386/cpu.o: in function `x86_cpu_filter_features':
>>> /tmp/pkgsrc-tmp/emulators/qemu/work/qemu-3.1.0/target/i386/cpu.c:5047:
>>> undefined reference to `kvm_arch_get_supported_cpuid'
>>> /usr/bin/ld:
>>> /tmp/pkgsrc-tmp/emulators/qemu/work/qemu-3.1.0/target/i386/cpu.c:5048:
>>> undefined reference to `kvm_arch_get_supported_cpuid'
>>> /usr/bin/ld:
>>> /tmp/pkgsrc-tmp/emulators/qemu/work/qemu-3.1.0/target/i386/cpu.c:5049:
>>> undefined reference to `kvm_arch_get_supported_cpuid'
>>> /usr/bin/ld:
>>> /tmp/pkgsrc-tmp/emulators/qemu/work/qemu-3.1.0/target/i386/cpu.c:5050:
>>> undefined reference to `kvm_arch_get_supported_cpuid'
>>> /usr/bin/ld:
>>> /tmp/pkgsrc-tmp/emulators/qemu/work/qemu-3.1.0/target/i386/cpu.c:5051:
>>> undefined reference to `kvm_arch_get_supported_cpuid'
>>> clang-9: error: linker command failed with exit code 1 (use -v to see
>>> invocation)
>>> make[1]: *** [Makefile:199: qemu-x86_64] Error 1
>>> gmake: *** [Makefile:483: subdir-x86_64-bsd-user] Error 2
>>> *** Error code 2
>>>
>>
>>
> 
>

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