KVM's --disable-gcc-check doesn't work

Bugs item #1807620, was opened at 2007-10-04 18:25
Message generated for change (Tracker Item Submitted) made by Item Submitter You can respond by visiting:
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Technologov (technologov)
Assigned to: Nobody/Anonymous (nobody)
Summary: KVM's --disable-gcc-check doesn't work

Initial Comment:
KVM's configure switch: "--disable-gcc-check" doesn't work.

This bug makes KVM very hard to compile on openSUSE 10.2/10.3, which, unlike Fedora doesn't have compat-gcc-34 package.

Here is the error:

alexey@suse103-home:~/Linstall/kvm-45> ./configure --disable-gcc-check ./configure: cannot locate gcc 3.x. please install it or specify with --qemu-cc

According to HELP, it should work:
alexey@suse103-home:~/Linstall/kvm-45> ./configure --help
Usage: ./configure [options]

Options include:

    --prefix=PREFIX        where to install things (/usr/local)
    --with-patched-kernel  don't use external module
    --kerneldir=DIR        kernel build directory (/lib/modules/2.6.22.5-31-bigsmp/build)

--qemu-cc="" compiler for qemu (needs gcc3.x) ()
--disable-gcc-check don't insist on gcc-3.x
- this will break running without kvm

Host: openSUSE 10.3, 32-bit, Intel Core 2 CPU, KVM-45.

-Alexey Technologov

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hi,
what's the real reason that kvm can't be compiled gcc-4.x? wouldn't it be better to be able to compile with the current compilers too?

  Levente                               "Si vis pacem para bellum!"

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Its actually an issue with QEMUs cpu emulation code. It takes advantage of compiler traits that are no longer true in the 4.x series. The code will actually compile under 4.x however. It just will not run properly. However, KVM doesn't use QEMUs cpu emulation, so if you do not care about running with KVM disabled (e.g. -no-kvm), you don't technically need to worry about it.

Hope that helps.
-Greg

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ok but now as qemu code was imported into kvm, then it's probably would be better to witch gcc-4.x?

  Levente                               "Si vis pacem para bellum!"

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Sure. Are you volunteering? ;) I'm sure both upstream QEMU developers, KVM developers, and the community using either would be most appreciative. I know I would be.

Regards,
-Greg

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here i mean that packaging kvm for fedora/redhat/centos using gcc-4.x in stead of gcc-3.x. if currently there is no reason to use gcc-3.x than i change all of my spec file.

ps. anyway it's planed to be temporary or permanent to use a qemu fork for kvm and not try to propagate changes back to the upstream qemu?

  Levente                               "Si vis pacem para bellum!"

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You *could*, sure. I have done this for local builds here. But if you go that route I would recommend making a patch to KVM so it doesn't fall back into QEMU mode automatically (today if it can't open the kvm module it will assume "-no-kvm" like behavior). Otherwise you will have a bunch of support calls about why its not working properly should someone cause the system to fall back.

Ill defer to Avi here, though as I understand it: Things that benefit the upstream source get pushed...things that are KVM only don't.

Regards,
-Greg

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And considering also there might be other yet unknown bugs because of gcc4, it is most likely better to stick to use gcc-3.x, unless there is really no other option.

For cases where no compat-gcc package is provided (like in OpenSUSE) then the following is IMHO the next best approach to force users to get gcc-3.x compiler installed from source just to be able to compile kvm.

Carlo

PS. please let me know what you think about it and if interested so I can provide the 3 patches (or more if more changes are needed) in a [PATCH] series for easy git-am'ing

---

index d9292fe..33a56d2 100755
@@ -63,8 +63,12 @@ while [[ "$1" = -* ]]; do
 done
 
 if [[ -z "$qemu_cc" ]]; then
-    echo "$0: cannot locate gcc 3.x. please install it or specify with --qemu-cc"
-    exit 1
+    if [[ -z "$disable_gcc_check" ]]; then
+        echo "$0: cannot locate gcc 3.x. please install it or specify with --qemu-cc"
+        exit 1
+    else
+        qemu_cc=gcc
+    fi
 fi
 
 libkvm_kerneldir="$kerneldir"

index fc1e59a..15549e3 100755
@@ -1022,6 +1022,11 @@ if test "$target_cpu" = "i386" ; then
   if test $kqemu = "yes" -a "$target_softmmu" = "yes" -a $cpu = "i386" ; then
     echo "#define USE_KQEMU 1" >> $config_h
   fi
+  if test $check_gcc = "no" ; then
+    if gcc -v 2>&1 | grep -q 'gcc *version *4\.[0-3]\.[0-9]'; then
+      echo "#define USE_GCC4 1" >> $config_h
+    fi
+  fi
   configure_kvm
 elif test "$target_cpu" = "arm" -o "$target_cpu" = "armeb" ; then
   echo "TARGET_ARCH=arm" >> $config_mak

@@ -1059,6 +1064,11 @@ elif test "$target_cpu" = "x86_64" ; then
   if test $kqemu = "yes" -a "$target_softmmu" = "yes" -a $cpu = "x86_64"  ; then
     echo "#define USE_KQEMU 1" >> $config_h
   fi
+  if test $check_gcc = "no" ; then
+    if gcc -v 2>&1 | grep -q 'gcc *version *4\.[0-3]\.[0-9]'; then
+      echo "#define USE_GCC4 1" >> $config_h
+    fi
+  fi
   configure_kvm
 elif test "$target_cpu" = "mips" -o "$target_cpu" = "mipsel" ; then
   echo "TARGET_ARCH=mips" >> $config_mak

index fe49d2c..2f78955 100644
@@ -8421,8 +8421,13 @@ int main(int argc, char **argv)
 #endif
 #ifdef USE_KVM
 	    case QEMU_OPTION_no_kvm:
+#ifdef USE_GCC4
+		fprintf(stderr, "Can't run without kvm if compiled with gcc4\n");
+		exit(1);
+#else
 		kvm_allowed = 0;
 		break;
+#endif
 	    case QEMU_OPTION_no_kvm_irqchip:
 		kvm_irqchip = 0;
 		break;

@@ -8552,8 +8557,13 @@ int main(int argc, char **argv)
 #if USE_KVM
     if (kvm_allowed) {
 	if (kvm_qemu_init() < 0) {
+#if USE_GCC4
+	    fprintf(stderr, "Could not initialize KVM, can't run without kvm if compiled with gcc4\n");
+	    exit(1);
+#else
 	    fprintf(stderr, "Could not initialize KVM, will disable KVM support\n");
 	    kvm_allowed = 0;
+#endif
 	}
     }
 #endif

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This will probably become more of a problem over time. GCC 3 is slated to be removed from the next Debian release:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=440425
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=440430

really good idea; and also as a side effect makes the patches independent as there is no need to have that qemu's configure glue anymore.

Carlo

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The plan is to submit everything to upstream qemu.

Any sufficiently difficult bug is indistinguishable from a feature.


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Here is a discussion thread about a patch by Michael Matz to make qemu's CPU emulation code actually work with gcc4:

http://www.nabble.com/-patch--make-qemu-work-with-GCC-4-t4345765.html

It's against the current qemu CVS, so as Avi updated kvm to qemu CVS now, it might be worth a try.

It means that the CPU emulation incurs a 3% performance regression, but the CPU emulation is only used when the CPU is not emulated by KVM in the kernel, so it should be a not a big concern for KVM, and if gcc4 would compile more efficent code for the device emulatoin, it could even lead to a theoritical speedup when KVM does CPU emulation, but that is a pure theory.

In this mail (which you do not see in the above thread view), a git repository with cumulated changes for qemu with gcc4 is mentioned, it seems to have further fixes on top of the initial patch:

http://www.mail-archive.com/[email protected]/msg12017.html

Bernhard Kaindl

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FWIW, there are patches that allow QEMU to compile and work with GCC 4 but, so far, certain folks in the QEMU community have objected strongly to them (look for the threads about post-processing GCC assembly output).

Those patches do work with KVM (and -no-kvm still works). However, it would be a bad idea to apply them to the KVM QEMU tree b/c it would make merging in the future much more difficult.

Regards,

Anthony Liguori

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This is a solution to the original problem with opensuse:

You can get gcc33 from the opensuse build service (this is the new one-click-install)
http://software.opensuse.org/ymp/devel%3Atools%3Agcc/openSUSE_10.3/i586/
gcc33-3.3.3-41.6.i586.rpm.ymp

(or download specific rpm's from http://software.opensuse.org/search by searching for gcc33).

Itamar

-----Original Message-----
From: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org [mailto:kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org] On Behalf Of SourceForge.net
Sent: Thursday, October 04, 2007 6:26 PM
To: [email protected]
Subject: [kvm-devel] [ kvm-Bugs-1807620 ] KVM's --disable-gcc-check doesn'twork

Bugs item #1807620, was opened at 2007-10-04 18:25 Message generated for change (Tracker Item Submitted) made by Item Submitter
You can respond by visiting:
https://sourceforge.net/tracker/?func=detail&atid=893831&aid=1807620&gro
up_id=180599

Please note that this message will contain a full copy of the comment thread,
including the initial issue submission, for this request, not just the latest update.
Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Technologov (technologov)
Assigned to: Nobody/Anonymous (nobody)
Summary: KVM's --disable-gcc-check doesn't work

Initial Comment:
KVM's configure switch: "--disable-gcc-check" doesn't work.

This bug makes KVM very hard to compile on openSUSE 10.2/10.3, which, unlike Fedora doesn't have compat-gcc-34 package.

Here is the error:

alexey@suse103-home:~/Linstall/kvm-45> ./configure --disable-gcc-check ./configure: cannot locate gcc 3.x. please install it or specify with --qemu-cc

According to HELP, it should work:
alexey@suse103-home:~/Linstall/kvm-45> ./configure --help
Usage: ./configure [options]

Options include:

    --prefix=PREFIX        where to install things (/usr/local)
    --with-patched-kernel  don't use external module
    --kerneldir=DIR        kernel build directory

(/lib/modules/2.6.22.5-31-bigsmp/build)
--qemu-cc="" compiler for qemu (needs gcc3.x) ()
--disable-gcc-check don't insist on gcc-3.x
- this will break running without kvm

Host: openSUSE 10.3, 32-bit, Intel Core 2 CPU, KVM-45.

-Alexey Technologov

----------------------------------------------------------------------

You can respond by visiting:
https://sourceforge.net/tracker/?func=detail&atid=893831&aid=1807620&gro
up_id=180599

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https://lists.sourceforge.net/lists/listinfo/kvm-devel

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