From: Paolo Bonzini <pbonzini@redhat.com>
To: Bill Wendling <morbo@google.com>, kvm@vger.kernel.org
Cc: oupton@google.com, drjones@redhat.com
Subject: Re: [kvm-unit-tests PATCH 5/7] svm: convert neg shift to unsigned shift
Date: Fri, 28 Feb 2020 12:12:52 +0100 [thread overview]
Message-ID: <a2429756-ccc5-6e01-fd12-34ecb5b8c05a@redhat.com> (raw)
In-Reply-To: <20200226094433.210968-10-morbo@google.com>
On 26/02/20 10:44, Bill Wendling wrote:
> Shifting a negative signed value is undefined. Use a shift of an
> unsigned value instead.
>
> Signed-off-by: Bill Wendling <morbo@google.com>
In practice only UBSAN complains; GCC even documents that it does not
treat it as undefined (which would be insane, especially if the
multiplication by 2 does not overflow as in this case):
GCC does not use the latitude given in C99 only to treat certain
aspects of signed '<<' as undefined, but this is subject to change.
But in the interest of purity we should instead compile with -fwrapv.
Paolo
> ---
> x86/svm.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/x86/svm.c b/x86/svm.c
> index ae85194..17be4b0 100644
> --- a/x86/svm.c
> +++ b/x86/svm.c
> @@ -1148,7 +1148,7 @@ static bool npt_rw_l1mmio_check(struct test *test)
> }
>
> #define TSC_ADJUST_VALUE (1ll << 32)
> -#define TSC_OFFSET_VALUE (-1ll << 48)
> +#define TSC_OFFSET_VALUE (~0ull << 48)
> static bool ok;
>
> static void tsc_adjust_prepare(struct test *test)
>
next prev parent reply other threads:[~2020-02-28 11:13 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-26 7:44 [kvm-unit-tests PATCH 0/7] Fixes for clang builds morbo
2020-02-26 7:44 ` [kvm-unit-tests PATCH 1/7] x86: emulator: use "SSE2" for the target morbo
2020-02-26 7:44 ` [kvm-unit-tests PATCH 2/7] pci: use uint32_t for unsigned long values morbo
2020-02-26 7:59 ` Andrew Jones
2020-02-26 9:02 ` Bill Wendling
2020-02-26 9:24 ` Andrew Jones
2020-02-26 7:44 ` [kvm-unit-tests PATCH 3/7] x86: realmode: syscall: add explicit size suffix to ambiguous instructions morbo
2020-02-26 7:44 ` [kvm-unit-tests PATCH 4/7] svm: change operand to output-only for matching constraint morbo
2020-02-26 7:44 ` [kvm-unit-tests PATCH 5/7] svm: convert neg shift to unsigned shift morbo
2020-02-26 7:44 ` [kvm-unit-tests PATCH 6/7] x86: VMX: use inline asm to get stack pointer morbo
2020-02-26 7:44 ` [kvm-unit-tests PATCH 7/7] x86: VMX: the "noclone" attribute is gcc-specific morbo
2020-02-26 8:21 ` Oliver Upton
2020-02-26 8:22 ` Oliver Upton
2020-02-26 9:44 ` [kvm-unit-tests PATCH v2 0/7] Fixes for clang builds Bill Wendling
2020-02-26 9:44 ` [kvm-unit-tests PATCH 1/7] x86: emulator: use "SSE2" for the target Bill Wendling
2020-02-26 9:44 ` [kvm-unit-tests PATCH v2 1/7] x86: pmu: Test WRMSR on a running counter Bill Wendling
2020-02-26 9:44 ` [kvm-unit-tests PATCH 2/7] pci: use uint32_t for unsigned long values Bill Wendling
2020-02-28 11:04 ` Paolo Bonzini
2020-02-28 12:46 ` Andrew Jones
2020-02-28 13:02 ` Paolo Bonzini
2020-02-26 9:44 ` [kvm-unit-tests PATCH v2 2/7] x86: provide enabled and disabled variation of the PCID test Bill Wendling
2020-02-26 9:44 ` [kvm-unit-tests PATCH v2 3/7] x86: pmu: Test perfctr overflow after WRMSR on a running counter Bill Wendling
2020-02-26 9:44 ` [kvm-unit-tests PATCH 3/7] x86: realmode: syscall: add explicit size suffix to ambiguous instructions Bill Wendling
2020-02-26 9:44 ` [kvm-unit-tests PATCH 4/7] svm: change operand to output-only for matching constraint Bill Wendling
2020-02-26 9:44 ` [kvm-unit-tests PATCH v2 4/7] vmx: tweak XFAILS for #DB test Bill Wendling
2020-02-26 9:44 ` [kvm-unit-tests PATCH 5/7] svm: convert neg shift to unsigned shift Bill Wendling
2020-02-28 11:12 ` Paolo Bonzini [this message]
2020-02-26 9:44 ` [kvm-unit-tests PATCH v2 5/7] x86: VMX: Add tests for monitor trap flag Bill Wendling
2020-02-26 9:44 ` [kvm-unit-tests PATCH v2 6/7] x86: emulator: use "SSE2" for the target Bill Wendling
2020-02-26 9:44 ` [kvm-unit-tests PATCH 6/7] x86: VMX: use inline asm to get stack pointer Bill Wendling
2020-02-26 9:44 ` [kvm-unit-tests PATCH v2 7/7] pci: cast masks to uint32_t for unsigned long values Bill Wendling
2020-02-26 9:44 ` [kvm-unit-tests PATCH 7/7] x86: VMX: the "noclone" attribute is gcc-specific Bill Wendling
2020-02-28 11:16 ` Paolo Bonzini
2020-02-28 18:19 ` Oliver Upton
2020-02-28 18:24 ` Paolo Bonzini
2020-02-28 18:40 ` Oliver Upton
2020-02-26 19:02 ` [kvm-unit-tests PATCH v2 0/7] Fixes for clang builds Oliver Upton
2020-02-26 20:12 ` [kvm-unit-tests PATCH v3 " Bill Wendling
2020-02-26 20:12 ` [kvm-unit-tests PATCH v3 1/7] x86: emulator: use "SSE2" for the target Bill Wendling
2020-02-26 20:12 ` [kvm-unit-tests PATCH v3 2/7] pci: cast masks to uint32_t for unsigned long values Bill Wendling
2020-02-26 20:12 ` [kvm-unit-tests PATCH v3 3/7] x86: realmode: syscall: add explicit size suffix to ambiguous instructions Bill Wendling
2020-02-26 20:12 ` [kvm-unit-tests PATCH v3 4/7] svm: change operand to output-only for matching constraint Bill Wendling
2020-02-26 20:12 ` [kvm-unit-tests PATCH v3 5/7] svm: convert neg shift to unsigned shift Bill Wendling
2020-02-26 20:12 ` [kvm-unit-tests PATCH v3 6/7] x86: VMX: use inline asm to get stack pointer Bill Wendling
2020-02-26 20:12 ` [kvm-unit-tests PATCH v3 7/7] x86: VMX: the "noclone" attribute is gcc-specific Bill Wendling
2020-02-27 2:05 ` Oliver Upton
2020-02-28 11:19 ` [kvm-unit-tests PATCH v2 0/7] Fixes for clang builds Paolo Bonzini
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