I don't have better names. Reviewed-by: Ray Ni <[email protected]>
> -----Original Message----- > From: [email protected] <[email protected]> On Behalf Of Marvin Häuser > Sent: Monday, August 16, 2021 9:10 PM > To: [email protected]; Ni, Ray <[email protected]> > Cc: Kinney, Michael D <[email protected]>; Liming Gao > <[email protected]>; Liu, Zhiguang > <[email protected]>; Vitaly Cheptsov <[email protected]> > Subject: Re: [edk2-devel] [PATCH V2 2/3] MdePkg/Base.h: Introduce various > alignment-related macros > > Hey Ray, > > On 16/08/2021 11:42, Ni, Ray wrote: > > Marvin, > > So lucky to have you in the edk2 project looking into these fundamentals! > > Thank you. :) > > > + #define ALIGNOF(TYPE) OFFSET_OF (struct { CHAR8 C; TYPE A; }, A) > > > > 1. Does struct{} inside a macro conform to C standard? How is the > > compatibility with different compilers? > > This should work, yes. The C standard defines offsetof as such: > > "The macros are [...] > > offsetof(type, member-designator) > > which expands to an integer constant expression that has type size_t, > the value of > which is the offset in bytes, to the structure member (designated by > member-designator), > from the beginning of its structure (designated by type). The type and > member designator > shall be such that given > > static type t; > > then the expression &(t.member-designator) evaluates to an address > constant. [...]" [1] > > If we plug in t: > > static struct { CHAR8 C; TYPE A; } t; > > we get a valid static storage duration variable declaration that > satisfies the the last condition because: > > "An address constant is [...], a pointer to an lvalue designating an > object of static > storage duration, or [...]" [2] > > It worked with all compilers I tinkered with at https://godbolt.org/ > I sadly do not have access to any of the compilers where this may be > used effectively (RVCT, EBC). > > > +#define IS_POW2(Value) ((Value) != 0U && ((Value) & ((Value) - 1U)) == > > +0U) > > > > 2. Good to me. I learned this trick when implementing the MtrrLib. > > > > +#define ALIGN_VALUE_ADDEND(Value, Alignment) (((Alignment) - (Value)) > > +& ((Alignment) - 1U)) > > > > 3. Is any other open source project using the same macro for the addend? > > This is actually a general question to all new macros. > > I would like the macros look familiar to developers from other open source > > projects. > > Good question, I never really saw it. I only came up with it because for > the new PE loader, we may align the PE memory within an underaligned > buffer, and for that we need the addend. I initially used to align up > and then subtract, but I saw this could be simplified with > ALIGN_VALUE_ADDEND, which was used in ALIGN_VALUE anyway. If you have a > better name, I'll change it. > > Best regards, > Marvin > > > [1] ISO/IEC 9899:2011, 7.19, 3. > > [2] ISO/IEC 9899:2011, 6.6, 9. > > > > > > > > > > > > > > > > -=-=-=-=-=-=-=-=-=-=-=- Groups.io Links: You receive all messages sent to this group. View/Reply Online (#79393): https://edk2.groups.io/g/devel/message/79393 Mute This Topic: https://groups.io/mt/84909448/21656 Group Owner: [email protected] Unsubscribe: https://edk2.groups.io/g/devel/unsub [[email protected]] -=-=-=-=-=-=-=-=-=-=-=-
