On Mon, Sep 30, 2024, Sean Christopherson wrote: > On Wed, Sep 11, 2024, Sean Christopherson wrote: > > Use u64_replace_bits() instead of u64p_replace_bits() to set PMCR.N in > > arm64's vPMU counter access test to fudge around what appears to be a gcc > > bug. With the recent change to have vcpu_get_reg() return a value in lieu > > of an out-param, some versions of gcc completely ignore the operation > > performed by set_pmcr_n(), i.e. ignore the output param. > > Filed a gcc bug: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=116912 > > I'll report back if anything interesting comes out of that bug. Well, there goes several hours that I'll never get back. Selftests are compiled with -O2, which enables strict-aliasing optimizations, and "unsigned long" and "unsigned long long" technically don't alias despite being the same size on 64-bit builds, so the compiler is allowed to optimize away the load. *sigh* I'll replace this with a patch to disable strict-aliasing, which the kernel has done since forever (literally predates git). Grr. diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile index 48d32c5aa3eb..a6f92129bb02 100644 --- a/tools/testing/selftests/kvm/Makefile +++ b/tools/testing/selftests/kvm/Makefile @@ -235,10 +235,10 @@ CFLAGS += -Wall -Wstrict-prototypes -Wuninitialized -O2 -g -std=gnu99 \ -Wno-gnu-variable-sized-type-not-at-end -MD -MP -DCONFIG_64BIT \ -fno-builtin-memcmp -fno-builtin-memcpy \ -fno-builtin-memset -fno-builtin-strnlen \ - -fno-stack-protector -fno-PIE -I$(LINUX_TOOL_INCLUDE) \ - -I$(LINUX_TOOL_ARCH_INCLUDE) -I$(LINUX_HDR_PATH) -Iinclude \ - -I$(<D) -Iinclude/$(ARCH_DIR) -I ../rseq -I.. $(EXTRA_CFLAGS) \ - $(KHDR_INCLUDES) + -fno-stack-protector -fno-PIE -fno-strict-aliasing \ + -I$(LINUX_TOOL_INCLUDE) -I$(LINUX_TOOL_ARCH_INCLUDE) \ + -I$(LINUX_HDR_PATH) -Iinclude -I$(<D) -Iinclude/$(ARCH_DIR) \ + -I ../rseq -I.. $(EXTRA_CFLAGS) $(KHDR_INCLUDES)
