[amd64] clean PRSTATUS_SIZE/SET_PR_FPVALID up properly

To get rid of hardcoded size/offset in those macros we need to have
a definition of i386 variant of struct elf_prstatus.  However, we can't
do that in asm/compat.h - the types needed for that are not there and
adding an include of asm/user32.h into asm/compat.h would cause a lot
of mess.

That could be conveniently done in elfcore-compat.h, but currently there
is nowhere to put arch-dependent parts of it - no asm/elfcore-compat.h.
So we introduce a new file (asm/elfcore-compat.h, present on architectures
that have CONFIG_ARCH_HAS_ELFCORE_COMPAT set, currently only on x86),
have it pulled by linux/elfcore-compat.h and move the definitions there.

As a side benefit, we don't need to worry about accidental inclusion of
that file into binfmt_elf.c itself, so we don't need the dance with
COMPAT_PRSTATUS_SIZE, etc. - only fs/compat_binfmt_elf.c will see
that header.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/Kconfig

@@ -1105,6 +1105,9 @@ config HAVE_ARCH_PFN_VALID
 config ARCH_SUPPORTS_DEBUG_PAGEALLOC
 	bool
 
+config ARCH_HAS_ELFCORE_COMPAT
+	bool
+
 source "kernel/gcov/Kconfig"
 
 source "scripts/gcc-plugins/Kconfig"

arch/x86/Kconfig

@@ -31,6 +31,7 @@ config X86_64
 	select MODULES_USE_ELF_RELA
 	select NEED_DMA_MAP_STATE
 	select SWIOTLB
+	select ARCH_HAS_ELFCORE_COMPAT
 
 config FORCE_DYNAMIC_FTRACE
 	def_bool y

arch/x86/include/asm/compat.h

@@ -159,20 +159,6 @@ struct compat_shmid64_ds {
 	compat_ulong_t __unused5;
 };
 
-/*
- * The type of struct elf_prstatus.pr_reg in compatible core dumps.
- */
-typedef struct user_regs_struct compat_elf_gregset_t;
-
-/* Full regset -- prstatus on x32, otherwise on ia32 */
-#define COMPAT_PRSTATUS_SIZE (user_64bit_mode(task_pt_regs(current)) \
-	? sizeof(struct compat_elf_prstatus) \
-	: 144)
-#define COMPAT_SET_PR_FPVALID(S) \
-	(*(user_64bit_mode(task_pt_regs(current)) \
-	       ? &(S)->pr_fpvalid	\
-               : (int *)((void *)(S) + 140)) = 1)
-
 #ifdef CONFIG_X86_X32_ABI
 #define COMPAT_USE_64BIT_TIME \
 	(!!(task_pt_regs(current)->orig_ax & __X32_SYSCALL_BIT))

arch/x86/include/asm/elfcore-compat.h

+#ifndef _ASM_X86_ELFCORE_COMPAT_H
+#define _ASM_X86_ELFCORE_COMPAT_H
+
+#include <asm/user32.h>
+
+/*
+ * On amd64 we have two 32bit ABIs - i386 and x32.  The latter
+ * has bigger registers, so we use it for compat_elf_regset_t.
+ * The former uses i386_elf_prstatus and PRSTATUS_SIZE/SET_PR_FPVALID
+ * are used to choose the size and location of ->pr_fpvalid of
+ * the layout actually used.
+ */
+typedef struct user_regs_struct compat_elf_gregset_t;
+
+struct i386_elf_prstatus
+{
+	struct compat_elf_prstatus_common	common;
+	struct user_regs_struct32		pr_reg;
+	compat_int_t			pr_fpvalid;
+};
+
+#define PRSTATUS_SIZE \
+	(user_64bit_mode(task_pt_regs(current)) \
+		? sizeof(struct compat_elf_prstatus) \
+		: sizeof(struct i386_elf_prstatus))
+#define SET_PR_FPVALID(S) \
+	(*(user_64bit_mode(task_pt_regs(current)) \
+		? &(S)->pr_fpvalid 	\
+		: &((struct i386_elf_prstatus *)(S))->pr_fpvalid) = 1)
+
+#endif

fs/compat_binfmt_elf.c

@@ -96,14 +96,6 @@
 #define	ELF_EXEC_PAGESIZE	COMPAT_ELF_EXEC_PAGESIZE
 #endif
 
-#ifdef	COMPAT_PRSTATUS_SIZE
-#define	PRSTATUS_SIZE COMPAT_PRSTATUS_SIZE
-#endif
-
-#ifdef	COMPAT_SET_PR_FPVALID
-#define	SET_PR_FPVALID(S) COMPAT_SET_PR_FPVALID(S)
-#endif
-
 #ifdef	COMPAT_ELF_PLAT_INIT
 #undef	ELF_PLAT_INIT
 #define	ELF_PLAT_INIT		COMPAT_ELF_PLAT_INIT

include/linux/elfcore-compat.h

@@ -33,13 +33,6 @@ struct compat_elf_prstatus_common
 	struct old_timeval32		pr_cstime;
 };
 
-struct compat_elf_prstatus
-{
-	struct compat_elf_prstatus_common	common;
-	compat_elf_gregset_t		pr_reg;
-	compat_int_t			pr_fpvalid;
-};
-
 struct compat_elf_prpsinfo
 {
 	char				pr_state;
@@ -54,4 +47,15 @@ struct compat_elf_prpsinfo
 	char				pr_psargs[ELF_PRARGSZ];
 };
 
+#ifdef CONFIG_ARCH_HAS_ELFCORE_COMPAT
+#include <asm/elfcore-compat.h>
+#endif
+
+struct compat_elf_prstatus
+{
+	struct compat_elf_prstatus_common	common;
+	compat_elf_gregset_t		pr_reg;
+	compat_int_t			pr_fpvalid;
+};
+
 #endif /* _LINUX_ELFCORE_COMPAT_H */