lkml.org 
[lkml]   [2021]   [Jul]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    SubjectRe: [PATCH 04/64] stddef: Introduce struct_group() helper macro
    On Fri, Jul 30, 2021 at 10:19:20PM +0000, Williams, Dan J wrote:
    > On Wed, 2021-07-28 at 14:59 -0700, Kees Cook wrote:
    > > On Wed, Jul 28, 2021 at 12:54:18PM +0200, Rasmus Villemoes wrote:
    > > > On 27/07/2021 22.57, Kees Cook wrote:
    > > >
    > > > > In order to have a regular programmatic way to describe a struct
    > > > > region that can be used for references and sizing, can be examined for
    > > > > bounds checking, avoids forcing the use of intermediate identifiers,
    > > > > and avoids polluting the global namespace, introduce the struct_group()
    > > > > macro. This macro wraps the member declarations to create an anonymous
    > > > > union of an anonymous struct (no intermediate name) and a named struct
    > > > > (for references and sizing):
    > > > >
    > > > >         struct foo {
    > > > >                 int one;
    > > > >                 struct_group(thing,
    > > > >                         int two,
    > > > >                         int three,
    > > > >                 );
    > > > >                 int four;
    > > > >         };
    > > >
    > > > That example won't compile, the commas after two and three should be
    > > > semicolons.
    > >
    > > Oops, yes, thanks. This is why I shouldn't write code that doesn't first
    > > go through a compiler. ;)
    > >
    > > > And your implementation relies on MEMBERS not containing any comma
    > > > tokens, but as
    > > >
    > > >   int a, b, c, d;
    > > >
    > > > is a valid way to declare multiple members, consider making MEMBERS
    > > > variadic
    > > >
    > > > #define struct_group(NAME, MEMBERS...)
    > > >
    > > > to have it slurp up every subsequent argument and make that work.
    > >
    > > Ah! Perfect, thank you. I totally forgot I could do it that way.
    >
    > This is great Kees. It just so happens it would clean-up what we are
    > already doing in drivers/cxl/cxl.h for anonymous + named register block
    > pointers. However in the cxl case it also needs the named structure to
    > be typed. Any appetite for a typed version of this?

    Oh cool! Yeah, totally I can expand it. Thanks for the suggestion!

    >
    > Here is a rough idea of the cleanup it would induce in drivers/cxl/:
    >
    > diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
    > index 53927f9fa77e..a2308c995654 100644
    > --- a/drivers/cxl/cxl.h
    > +++ b/drivers/cxl/cxl.h
    > @@ -75,52 +75,19 @@ static inline int cxl_hdm_decoder_count(u32 cap_hdr)
    > #define CXLDEV_MBOX_BG_CMD_STATUS_OFFSET 0x18
    > #define CXLDEV_MBOX_PAYLOAD_OFFSET 0x20
    >
    > -#define CXL_COMPONENT_REGS() \
    > - void __iomem *hdm_decoder
    > -
    > -#define CXL_DEVICE_REGS() \
    > - void __iomem *status; \
    > - void __iomem *mbox; \
    > - void __iomem *memdev
    > -
    > -/* See note for 'struct cxl_regs' for the rationale of this organization */
    > /*
    > - * CXL_COMPONENT_REGS - Common set of CXL Component register block base pointers
    > * @hdm_decoder: CXL 2.0 8.2.5.12 CXL HDM Decoder Capability Structure
    > - */
    > -struct cxl_component_regs {
    > - CXL_COMPONENT_REGS();
    > -};
    > -
    > -/* See note for 'struct cxl_regs' for the rationale of this organization */
    > -/*
    > - * CXL_DEVICE_REGS - Common set of CXL Device register block base pointers
    > * @status: CXL 2.0 8.2.8.3 Device Status Registers
    > * @mbox: CXL 2.0 8.2.8.4 Mailbox Registers
    > * @memdev: CXL 2.0 8.2.8.5 Memory Device Registers
    > */
    > -struct cxl_device_regs {
    > - CXL_DEVICE_REGS();
    > -};
    > -
    > -/*
    > - * Note, the anonymous union organization allows for per
    > - * register-block-type helper routines, without requiring block-type
    > - * agnostic code to include the prefix.
    > - */
    > struct cxl_regs {
    > - union {
    > - struct {
    > - CXL_COMPONENT_REGS();
    > - };
    > - struct cxl_component_regs component;
    > - };
    > - union {
    > - struct {
    > - CXL_DEVICE_REGS();
    > - };
    > - struct cxl_device_regs device_regs;
    > - };
    > + struct_group_typed(cxl_component_regs, component,
    > + void __iomem *hdm_decoder;
    > + );
    > + struct_group_typed(cxl_device_regs, device_regs,
    > + void __iomem *status, *mbox, *memdev;
    > + );
    > };
    >
    > struct cxl_reg_map {
    > diff --git a/include/linux/stddef.h b/include/linux/stddef.h
    > index cf7f866944f9..84b7de24ffb5 100644
    > --- a/include/linux/stddef.h
    > +++ b/include/linux/stddef.h
    > @@ -49,12 +49,18 @@ enum {
    > * @ATTRS: Any struct attributes (normally empty)
    > * @MEMBERS: The member declarations for the mirrored structs
    > */
    > -#define struct_group_attr(NAME, ATTRS, MEMBERS) \
    > +#define struct_group_attr(NAME, ATTRS, MEMBERS...) \
    > union { \
    > struct { MEMBERS } ATTRS; \
    > struct { MEMBERS } ATTRS NAME; \
    > }
    >
    > +#define struct_group_attr_typed(TYPE, NAME, ATTRS, MEMBERS...) \
    > + union { \
    > + struct { MEMBERS } ATTRS; \
    > + struct TYPE { MEMBERS } ATTRS NAME; \
    > + }
    > +
    > /**
    > * struct_group(NAME, MEMBERS)
    > *
    > @@ -67,7 +73,10 @@ enum {
    > * @NAME: The name of the mirrored sub-struct
    > * @MEMBERS: The member declarations for the mirrored structs
    > */
    > -#define struct_group(NAME, MEMBERS) \
    > +#define struct_group(NAME, MEMBERS...) \
    > struct_group_attr(NAME, /* no attrs */, MEMBERS)
    >
    > +#define struct_group_typed(TYPE, NAME, MEMBERS...) \
    > + struct_group_attr_typed(TYPE, NAME, /* no attrs */, MEMBERS)
    > +
    > #endif

    Awesome! My instinct is to expose the resulting API as:

    __struct_group(type, name, attrs, members...)

    struct_group(name, members...)
    struct_group_attr(name, attrs, members...)
    struct_group_typed(type, name, members...)

    --
    Kees Cook

    \
     
     \ /
      Last update: 2021-07-31 05:00    [W:4.141 / U:0.460 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site