On 11/9/23 14:32, Kevin Wolf wrote:
Am 11.09.2023 um 13:15 hat Stefan Hajnoczi geschrieben:
On Mon, 11 Sept 2023 at 06:39, Philippe Mathieu-Daudé <philmd@xxxxxxxxxx> wrote:
Since commits 3adce820cf..ef1cf6890f, When building on
a x86 host configured as:
$ ./configure --cc=clang \
--target-list=x86_64-linux-user,x86_64-softmmu \
--enable-debug
we get:
[71/71] Linking target qemu-x86_64
FAILED: qemu-x86_64
/usr/bin/ld: libqemu-x86_64-linux-user.fa.p/target_i386_cpu.c.o: in function `cpu_x86_cpuid':
cpu.c:(.text+0x1374): undefined reference to `kvm_arch_get_supported_cpuid'
/usr/bin/ld: libqemu-x86_64-linux-user.fa.p/target_i386_cpu.c.o: in function `x86_cpu_filter_features':
cpu.c:(.text+0x81c2): undefined reference to `kvm_arch_get_supported_cpuid'
/usr/bin/ld: cpu.c:(.text+0x81da): undefined reference to `kvm_arch_get_supported_cpuid'
/usr/bin/ld: cpu.c:(.text+0x81f2): undefined reference to `kvm_arch_get_supported_cpuid'
/usr/bin/ld: cpu.c:(.text+0x820a): undefined reference to `kvm_arch_get_supported_cpuid'
/usr/bin/ld: libqemu-x86_64-linux-user.fa.p/target_i386_cpu.c.o:cpu.c:(.text+0x8225): more undefined references to `kvm_arch_get_supported_cpuid' follow
clang: error: linker command failed with exit code 1 (use -v to see invocation)
ninja: build stopped: subcommand failed.
'--enable-debug' disables optimizations (CFLAGS=-O0).
While at this (un)optimization level GCC eliminate the
following dead code:
if (0 && foo()) {
...
}
Clang does not. Therefore restore a pair of stubs for
unoptimized Clang builds.
Reported-by: Kevin Wolf <kwolf@xxxxxxxxxx>
Fixes: 3adce820cf ("target/i386: Remove unused KVM stubs")
Fixes: ef1cf6890f ("target/i386: Allow elision of kvm_hv_vpindex_settable()")
Signed-off-by: Philippe Mathieu-Daudé <philmd@xxxxxxxxxx>
---
target/i386/kvm/kvm_i386.h | 21 ++++++++++++++++++---
1 file changed, 18 insertions(+), 3 deletions(-)
+#elif defined(__clang__) && !defined(__OPTIMIZE__)
Another approach is a static library with a .o file containing the
stubs so the linker only includes it in the executable if the compiler
emitted the symbols. That way there is no need for defined(__clang__)
&& !defined(__OPTIMIZE__) and it will work with other
compilers/optimization levels. It's more work to set up though.
Isn't that exactly how it was before the stubs were removed? It would be
a simple revert of that commit.
The approach with static inline functions defined only for a very
specific configuration looks a lot more fragile to me. In fact, I'm
surprised that it works because I think it requires that the header
isn't used in any files that are shared between user space and system
emulation - and naively cpu.c sounded like something that could be
shared. Looks like this patch only works because the linux-user target
uses a separate build of the same CPU emulation source file.
So I think reverting the commit that removed the stubs would be much
more obvious.
Yes, v2 reverts:
https://lore.kernel.org/qemu-devel/20230911131507.24943-1-philmd@xxxxxxxxxx/
