There is a case must be considered that gEventPending is 0, HighBitSet64 will return -1, then the code will be wrong. The code maybe:
while (gEventPending != 0) { PendingTpl = (UINTN) HighBitSet64 (gEventPending); if (NewTpl >= PendingTpl) { break; } gEfiCurrentTpl = PendingTpl; ... } Thanks, Star -----Original Message----- From: edk2-devel [mailto:edk2-devel-boun...@lists.01.org] On Behalf Of Paolo Bonzini Sent: Wednesday, September 20, 2017 1:03 AM To: Wu, Hao A <hao.a...@intel.com>; edk2-devel@lists.01.org Cc: Dong, Eric <eric.d...@intel.com>; Zeng, Star <star.z...@intel.com> Subject: Re: [edk2] [PATCH 3/6] MdeModulePkg/Tpl: Fix negative value left shift On 19/09/2017 13:43, Hao Wu wrote: > REF: https://bugzilla.tianocore.org/show_bug.cgi?id=695 > > Within function CoreRestoreTpl(), left shift a negative value -2 is > used > in: > "while (((-2 << NewTpl) & gEventPending) != 0) {" > > which involves undefined behavior. > > According to the C11 spec, Section 6.5.7: >> 4 The result of E1 << E2 is E1 left-shifted E2 bit positions; vacated >> bits are filled with zeros. If E1 has an unsigned type, the value >> of the result is E1 * 2^E2 , reduced modulo one more than the >> maximum value representable in the result type. If E1 has a signed >> type and nonnegative value, and E1 * 2^E2 is representable in the >> result type, then that is the resulting value; otherwise, the >> behavior is undefined. > > This commit explicitly cast '-2' with UINTN to resolve this issue. > > Cc: Steven Shi <steven....@intel.com> > Cc: Star Zeng <star.z...@intel.com> > Cc: Eric Dong <eric.d...@intel.com> > Contributed-under: TianoCore Contribution Agreement 1.1 > Signed-off-by: Hao Wu <hao.a...@intel.com> > --- > MdeModulePkg/Core/Dxe/Event/Tpl.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/MdeModulePkg/Core/Dxe/Event/Tpl.c > b/MdeModulePkg/Core/Dxe/Event/Tpl.c > index 8ad0a33701..8c50f61117 100644 > --- a/MdeModulePkg/Core/Dxe/Event/Tpl.c > +++ b/MdeModulePkg/Core/Dxe/Event/Tpl.c > @@ -123,7 +123,7 @@ CoreRestoreTpl ( > // > // Dispatch any pending events > // > - while (((-2 << NewTpl) & gEventPending) != 0) { > + while (((((UINTN)-2) << NewTpl) & gEventPending) != 0) { > gEfiCurrentTpl = (UINTN) HighBitSet64 (gEventPending); > if (gEfiCurrentTpl < TPL_HIGH_LEVEL) { > CoreSetInterruptState (TRUE); > Maybe: for (;;) { PendingTpl = (UINTN) HighBitSet64 (gEventPending); if (NewTpl >= PendingTpl) { break; } gEfiCurrentTpl = PendingTpl; } This is much more readable, and HighBitSet64 should be efficient on most modern processors. Paolo _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel _______________________________________________ edk2-devel mailing list edk2-devel@lists.01.org https://lists.01.org/mailman/listinfo/edk2-devel