Re: [PATCH] target/i386: Re-introduce few KVM stubs for Clang debug builds

["Daniel P. Berrangé" <berrange@redhat.com>]

On Mon, Sep 11, 2023 at 12:38:32PM +0200, Philippe Mathieu-Daudé 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@redhat.com>
> Fixes: 3adce820cf ("target/i386: Remove unused KVM stubs")
> Fixes: ef1cf6890f ("target/i386: Allow elision of kvm_hv_vpindex_settable()")

Why not just revert those two commits, since we now learned the rationale
for them was incorrect ?

> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> ---
>  target/i386/kvm/kvm_i386.h | 21 ++++++++++++++++++---
>  1 file changed, 18 insertions(+), 3 deletions(-)

With regards,
Daniel
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