Am 11.09.2023 um 16:27 hat Philippe Mathieu-Daudé geschrieben:
> Since commits 3adce820cf ("target/i386: Remove unused KVM
> stubs") and ef1cf6890f ("target/i386: Allow elision of
> kvm_hv_vpindex_settable()"), 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.
>
> libqemu-x86_64-linux-user.fa is user emulation specific, so
> having system emulation code called there is dubious.
>
> '--enable-debug' disables optimizations (CFLAGS=-O0).
>
> While at this (un)optimization level GCC eliminate the
> following dead code (CPP output of mentioned build):
>
> static void x86_cpu_get_supported_cpuid(uint32_t func, uint32_t index,
> uint32_t *eax, uint32_t *ebx,
> uint32_t *ecx, uint32_t *edx)
> {
> if ((0)) {
> *eax = kvm_arch_get_supported_cpuid(kvm_state, func, index, R_EAX);
> *ebx = kvm_arch_get_supported_cpuid(kvm_state, func, index, R_EBX);
> *ecx = kvm_arch_get_supported_cpuid(kvm_state, func, index, R_ECX);
> *edx = kvm_arch_get_supported_cpuid(kvm_state, func, index, R_EDX);
> } else if (0) {
> *eax = 0;
> *ebx = 0;
> *ecx = 0;
> *edx = 0;
> } else {
> *eax = 0;
> *ebx = 0;
> *ecx = 0;
> *edx = 0;
> }
> }
>
> Clang does not.
>
> Instead of trying to deal with compiler specific checks around
> __OPTIMIZE__ (see commit 2140cfa51d "i386: Fix build by providing
> stub kvm_arch_get_supported_cpuid()"), simply restrict code
> belonging to system emulation, easing user emulation linking.
>
> Reported-by: Kevin Wolf <kwolf@xxxxxxxxxx>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@xxxxxxxxxx>
Can we make the function declarations in the header file for the
functions without stubs conditional on !CONFIG_USER_ONLY, too, so that
trying to call them would already fail during compilation (and also with
-O2), not only when linking without optimisations?
Kevin
