On Sat, Jul 8, 2023 at 3:24 PM Stefano Stabellini <sstabell...@kernel.org>
wrote:
> On Sat, 1 Jul 2023, Christopher Clark wrote:
> > Pointer fields within structs need to be defined as fixed size types in
> > the x86 boot build environment. Using a typedef for the field type
> > rather than a struct pointer type enables the type definition to
> > be changed in the 32-bit boot build and the main hypervisor build,
> > allowing for a single common structure definition and a common header
> file.
>
> Sorry for my ignorance, but why?
>
> struct boot_module is not used as part of any ABI, right? It is
> populated by Xen at boot by hand. Why do we need a specific memory
> layout for it?
>
Fair question! In the early x86 boot logic, which runs in 32-bit CPU mode,
struct boot_module is allocated and populated, so the structure needs to be
defined and available to code that is compiled in 32-bit to do that. The
same structures are also accessed later in 64-bit hypervisor logic, and the
memory layout of the structure needs to be the same in both cases, so we
want all the fields to be fixed-width types, and that includes pointers.
These macros help with declaring pointers as always-64-bit-sized struct
fields in a single definition of the struct. They're not strictly necessary
though - providing alternative definitions for typedefs can be used
instead, and I've been looking at doing that since posting this patch.
Christopher
>
>
>
> > Introduces DEFINE_STRUCT_PTR_TYPE and DEFINE_PTR_TYPE which will
> > generate typedefs with a _ptr_t suffix for pointers to the specified
> > type. This is then used in <xen/bootinfo.h> for pointers within structs
> > as preparation for using these headers in the x86 boot build.
> >
> > The 32-bit behaviour is obtained by inclusion of "defs.h" first with a
> > check for such an existing definition on the <xen/types.h> version.
> >
> > paddr_t is used in <xen/bootinfo.h> so a definition is added here to
> > the x86 boot environment defs.h header.
> >
> > Signed-off-by: Christopher Clark <christopher.w.cl...@gmail.com>
> > Signed-off-by: Daniel P. Smith <dpsm...@apertussolutions.com>
>
>
> > ---
> > Changes since v2: This is two v2 patches merged into one for v3.
> > Changes since v1: New in v2 of series.
> >
> > xen/arch/x86/boot/defs.h | 9 +++++++++
> > xen/arch/x86/include/asm/bootinfo.h | 4 +++-
> > xen/include/xen/bootinfo.h | 9 +++++----
> > xen/include/xen/types.h | 11 +++++++++++
> > 4 files changed, 28 insertions(+), 5 deletions(-)
> >
> > diff --git a/xen/arch/x86/boot/defs.h b/xen/arch/x86/boot/defs.h
> > index f9840044ec..bc0f1b5cf8 100644
> > --- a/xen/arch/x86/boot/defs.h
> > +++ b/xen/arch/x86/boot/defs.h
> > @@ -60,4 +60,13 @@ typedef u64 uint64_t;
> > #define U16_MAX ((u16)(~0U))
> > #define UINT_MAX (~0U)
> >
> > +typedef unsigned long long paddr_t;
> > +
> > +#define DEFINE_STRUCT_PTR_TYPE(struct_name) \
> > + typedef uint64_t struct_name ## _ptr_t;
> > +
> > +#define DEFINE_PTR_TYPE(type) \
> > + typedef uint64_t type ## _ptr_t;
> > +DEFINE_PTR_TYPE(char);
> > +
> > #endif /* __BOOT_DEFS_H__ */
> > diff --git a/xen/arch/x86/include/asm/bootinfo.h
> b/xen/arch/x86/include/asm/bootinfo.h
> > index 30c27980e0..989fb7a1da 100644
> > --- a/xen/arch/x86/include/asm/bootinfo.h
> > +++ b/xen/arch/x86/include/asm/bootinfo.h
> > @@ -6,6 +6,7 @@ struct arch_bootmodule {
> > uint32_t flags;
> > unsigned headroom;
> > };
> > +DEFINE_STRUCT_PTR_TYPE(arch_bootmodule);
> >
> > struct arch_boot_info {
> > uint32_t flags;
> > @@ -14,11 +15,12 @@ struct arch_boot_info {
> > #define BOOTINFO_FLAG_X86_MEMMAP 1U << 6
> > #define BOOTINFO_FLAG_X86_LOADERNAME 1U << 9
> >
> > - char *boot_loader_name;
> > + char_ptr_t boot_loader_name;
> >
> > uint32_t mmap_length;
> > paddr_t mmap_addr;
> > };
> > +DEFINE_STRUCT_PTR_TYPE(arch_boot_info);
> >
> > struct __packed mb_memmap {
> > uint32_t size;
> > diff --git a/xen/include/xen/bootinfo.h b/xen/include/xen/bootinfo.h
> > index 2f4284a91f..8389da4f72 100644
> > --- a/xen/include/xen/bootinfo.h
> > +++ b/xen/include/xen/bootinfo.h
> > @@ -35,17 +35,18 @@ struct boot_module {
> > mfn_t mfn;
> > size_t size;
> >
> > - struct arch_bootmodule *arch;
> > + arch_bootmodule_ptr_t arch;
> > struct boot_string string;
> > };
> > +DEFINE_STRUCT_PTR_TYPE(boot_module);
> >
> > struct boot_info {
> > - char *cmdline;
> > + char_ptr_t cmdline;
> >
> > unsigned int nr_mods;
> > - struct boot_module *mods;
> > + boot_module_ptr_t mods;
> >
> > - struct arch_boot_info *arch;
> > + arch_boot_info_ptr_t arch;
> > };
> >
> > #endif
> > diff --git a/xen/include/xen/types.h b/xen/include/xen/types.h
> > index 6aba80500a..e807ffe255 100644
> > --- a/xen/include/xen/types.h
> > +++ b/xen/include/xen/types.h
> > @@ -71,4 +71,15 @@ typedef bool bool_t;
> > #define test_and_set_bool(b) xchg(&(b), true)
> > #define test_and_clear_bool(b) xchg(&(b), false)
> >
> > +#ifndef DEFINE_STRUCT_PTR_TYPE
> > +#define DEFINE_STRUCT_PTR_TYPE(struct_name) \
> > + typedef struct struct_name * struct_name ## _ptr_t;
> > +#endif
> > +
> > +#ifndef DEFINE_PTR_TYPE
> > +#define DEFINE_PTR_TYPE(type) \
> > + typedef type * type ## _ptr_t;
> > +DEFINE_PTR_TYPE(char);
> > +#endif
> > +
> > #endif /* __TYPES_H__ */
> > --
> > 2.25.1
> >
> >
>
