arch: provide better documentation for the arch-specific SA_* flags

Instead of documenting the arch-specific flag values in a comment at
the top where they may be easily overlooked, document them in comments
inline with the definitions in numerical order so that it is clear
why specific values must be chosen for new generic flags and to reduce
the likelihood of conflicts between generic and arch-specific flags.

Signed-off-by: Peter Collingbourne <pcc@google.com>
Link: https://linux-review.googlesource.com/id/I40a129cf7c3a71ba1bfd6d936c544072ee3b7ce6
Link: https://lkml.kernel.org/r/198c8b68c76bf3ed73117d817c7cdf9bc0eb174f.1605582887.git.pcc@google.com
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

include/uapi/asm-generic/signal-defs.h

@@ -17,9 +17,6 @@
  *
  * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single
  * Unix names RESETHAND and NODEFER respectively.
- *
- * The following bits are used in architecture-specific SA_* definitions and
- * should be avoided for new generic flags: 3, 4, 5, 6, 7, 8, 9, 16, 24, 25, 26.
  */
 #ifndef SA_NOCLDSTOP
 #define SA_NOCLDSTOP	0x00000001
@@ -30,6 +27,20 @@
 #ifndef SA_SIGINFO
 #define SA_SIGINFO	0x00000004
 #endif
+/* 0x00000008 used on alpha, mips, parisc */
+/* 0x00000010 used on alpha, parisc */
+/* 0x00000020 used on alpha, parisc, sparc */
+/* 0x00000040 used on alpha, parisc */
+/* 0x00000080 used on parisc */
+/* 0x00000100 used on sparc */
+/* 0x00000200 used on sparc */
+/* 0x00010000 used on mips */
+/* 0x01000000 used on x86 */
+/* 0x02000000 used on x86 */
+/*
+ * New architectures should not define the obsolete
+ *	SA_RESTORER	0x04000000
+ */
 #ifndef SA_ONSTACK
 #define SA_ONSTACK	0x08000000
 #endif
@@ -46,11 +57,6 @@
 #define SA_NOMASK	SA_NODEFER
 #define SA_ONESHOT	SA_RESETHAND
 
-/*
- * New architectures should not define the obsolete
- *	SA_RESTORER	0x04000000
- */
-
 #ifndef SIG_BLOCK
 #define SIG_BLOCK          0	/* for blocking signals */
 #endif