x86/headers: Clean up uapi/asm/sigcontext32.h

Clean up sigcontext32.h a bit:

 - use consistent and readable vertical spacing
 - fix, harmonize and extend comments

No field name has been changed, user-space might be relying on
them.
Acked-by: NMikko Rapeli <mikko.rapeli@iki.fi>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/1441438363-9999-3-git-send-email-mingo@kernel.orgSigned-off-by: NIngo Molnar <mingo@kernel.org>

arch/x86/include/uapi/asm/sigcontext32.h

 #ifndef _ASM_X86_SIGCONTEXT32_H
 #define _ASM_X86_SIGCONTEXT32_H
 
+/* Signal context definitions for compat 32-bit programs: */
+
 #include <linux/types.h>
 
 #include <asm/sigcontext.h>
 
-/* signal context for 32bit programs. */
-
-#define X86_FXSR_MAGIC		0x0000
-
+/* 10-byte legacy floating point register: */
 struct _fpreg {
-	unsigned short significand[4];
-	unsigned short exponent;
+	unsigned short			significand[4];
+	unsigned short			exponent;
 };
 
+/* 16-byte floating point register: */
 struct _fpxreg {
-	unsigned short significand[4];
-	unsigned short exponent;
-	unsigned short padding[3];
+	unsigned short			significand[4];
+	unsigned short			exponent;
+	unsigned short			padding[3];
 };
 
+/* 16-byte XMM vector register: */
 struct _xmmreg {
 	__u32	element[4];
 };
 
-/* FSAVE frame with extensions */
+#define X86_FXSR_MAGIC			0x0000
+
+/* FXSAVE frame: FSAVE frame with extensions */
 struct _fpstate_ia32 {
-	/* Regular FPU environment */
-	__u32 	cw;
-	__u32	sw;
-	__u32	tag;	/* not compatible to 64bit twd */
-	__u32	ipoff;
-	__u32	cssel;
-	__u32	dataoff;
-	__u32	datasel;
-	struct _fpreg	_st[8];
-	unsigned short	status;
-	unsigned short	magic;		/* 0xffff = regular FPU data only */
+	/* Regular FPU environment: */
+	__u32				cw;
+	__u32				sw;
+	__u32				tag;		/* Not compatible with the 64-bit frame */
+	__u32				ipoff;
+	__u32				cssel;
+	__u32				dataoff;
+	__u32				datasel;
+	struct _fpreg			_st[8];
+	unsigned short			status;
+	unsigned short			magic;		/* 0xffff: regular FPU data only */
+							/* 0x0000: FXSR data */
 
-	/* FXSR FPU environment */
-	__u32	_fxsr_env[6];
-	__u32	mxcsr;
-	__u32	reserved;
-	struct _fpxreg	_fxsr_st[8];
-	struct _xmmreg	_xmm[8];	/* It's actually 16 */
-	__u32	padding[44];
+	/* Extended FXSR FPU environment: */
+	__u32				_fxsr_env[6];
+	__u32				mxcsr;
+	__u32				reserved;
+	struct _fpxreg			_fxsr_st[8];
+	struct _xmmreg			_xmm[8];	/* The first  8 XMM registers */
+	__u32				padding[44];	/* The second 8 XMM registers plus padding */
 	union {
-		__u32 padding2[12];
-		struct _fpx_sw_bytes sw_reserved;
+		__u32			padding2[12];
+		/* Might encode xstate extensions, see asm/sigcontext.h: */
+		struct _fpx_sw_bytes	sw_reserved;
 	};
 };
 
+/* 32-bit compat sigcontext: */
 struct sigcontext_ia32 {
-       unsigned short gs, __gsh;
-       unsigned short fs, __fsh;
-       unsigned short es, __esh;
-       unsigned short ds, __dsh;
-       unsigned int di;
-       unsigned int si;
-       unsigned int bp;
-       unsigned int sp;
-       unsigned int bx;
-       unsigned int dx;
-       unsigned int cx;
-       unsigned int ax;
-       unsigned int trapno;
-       unsigned int err;
-       unsigned int ip;
-       unsigned short cs, __csh;
-       unsigned int flags;
-       unsigned int sp_at_signal;
-       unsigned short ss, __ssh;
-       unsigned int fpstate;		/* really (struct _fpstate_ia32 *) */
-       unsigned int oldmask;
-       unsigned int cr2;
+       unsigned short			gs, __gsh;
+       unsigned short			fs, __fsh;
+       unsigned short			es, __esh;
+       unsigned short			ds, __dsh;
+       unsigned int			di;
+       unsigned int			si;
+       unsigned int			bp;
+       unsigned int			sp;
+       unsigned int			bx;
+       unsigned int			dx;
+       unsigned int			cx;
+       unsigned int			ax;
+       unsigned int			trapno;
+       unsigned int			err;
+       unsigned int			ip;
+       unsigned short			cs, __csh;
+       unsigned int			flags;
+       unsigned int			sp_at_signal;
+       unsigned short			ss, __ssh;
+       unsigned int			fpstate;	/* Pointer to 'struct _fpstate_ia32' */
+       unsigned int			oldmask;
+       unsigned int			cr2;
 };
 
 #endif /* _ASM_X86_SIGCONTEXT32_H */