Re: [PATCH 04/64] stddef: Introduce struct_group() helper macro

Re: [PATCH 04/64] stddef: Introduce struct_group() helper macro

[Williams, Dan J]

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?

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

Re: [PATCH 04/64] stddef: Introduce struct_group() helper macro

[Kees Cook]

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

Re: [PATCH 04/64] stddef: Introduce struct_group() helper macro

[Kees Cook]

On Sat, Jul 31, 2021 at 07:24:44AM +0200, Rasmus Villemoes wrote:
> On Sat, Jul 31, 2021, 04:59 Kees Cook <keescook@chromium.org> wrote:
> 
> > 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:
> >
> > >  /**
> > >   * 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...)
> 
> Bikeshed: can we use proper nomenclature please. s/type/tag/,
> s/typed/tagged.

Ah! Thank you. I went looking for the spec on what these are called and
couldn't find it. "struct $tag" is the type, then, yes? So IIUC now:

       |    type   | members  | name
       |       tag
	struct foo { int bar; } baz;

-- 
Kees Cook