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

["Williams, Dan J" <dan.j.williams@intel.com>]

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