Star and Paolo, Thanks for the feedbacks. I will refine the patch according to your suggestions.
Best Regards, Hao Wu > -----Original Message----- > From: Zeng, Star > Sent: Thursday, September 21, 2017 10:57 AM > To: Paolo Bonzini; Wu, Hao A; [email protected] > Cc: Dong, Eric; Zeng, Star > Subject: RE: [edk2] [PATCH 3/6] MdeModulePkg/Tpl: Fix negative value left > shift > > 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:[email protected]] On Behalf Of Paolo > Bonzini > Sent: Wednesday, September 20, 2017 1:03 AM > To: Wu, Hao A <[email protected]>; [email protected] > Cc: Dong, Eric <[email protected]>; Zeng, Star <[email protected]> > 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 <[email protected]> > > Cc: Star Zeng <[email protected]> > > Cc: Eric Dong <[email protected]> > > Contributed-under: TianoCore Contribution Agreement 1.1 > > Signed-off-by: Hao Wu <[email protected]> > > --- > > 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 > [email protected] > https://lists.01.org/mailman/listinfo/edk2-devel _______________________________________________ edk2-devel mailing list [email protected] https://lists.01.org/mailman/listinfo/edk2-devel
