1 files changed, 55 insertions, 0 deletions

diff --git a/arch/arm64/include/uapi/asm/sigcontext.h b/arch/arm64/include/uapi/asm/sigcontext.h
index ee469be1ae1d..f0a76b9fcd6e 100644
--- a/arch/arm64/include/uapi/asm/sigcontext.h
+++ b/arch/arm64/include/uapi/asm/sigcontext.h
@@ -34,6 +34,26 @@ struct sigcontext {
 };
 
 /*
+ * Allocation of __reserved[]:
+ * (Note: records do not necessarily occur in the order shown here.)
+ *
+ *	size		description
+ *
+ *	0x210		fpsimd_context
+ *	 0x10		esr_context
+ *	 0x20		extra_context (optional)
+ *	 0x10		terminator (null _aarch64_ctx)
+ *
+ *	0xdb0		(reserved for future allocation)
+ *
+ * New records that can exceed this space need to be opt-in for userspace, so
+ * that an expanded signal frame is not generated unexpectedly.  The mechanism
+ * for opting in will depend on the extension that generates each new record.
+ * The above table documents the maximum set and sizes of records than can be
+ * generated when userspace does not opt in for any such extension.
+ */
+
+/*
  * Header to be used at the beginning of structures extending the user
  * context. Such structures must be placed after the rt_sigframe on the stack
  * and be 16-byte aligned. The last structure must be a dummy one with the
@@ -61,4 +81,39 @@ struct esr_context {
 	__u64 esr;
 };
 
+/*
+ * extra_context: describes extra space in the signal frame for
+ * additional structures that don't fit in sigcontext.__reserved[].
+ *
+ * Note:
+ *
+ * 1) fpsimd_context, esr_context and extra_context must be placed in
+ * sigcontext.__reserved[] if present.  They cannot be placed in the
+ * extra space.  Any other record can be placed either in the extra
+ * space or in sigcontext.__reserved[], unless otherwise specified in
+ * this file.
+ *
+ * 2) There must not be more than one extra_context.
+ *
+ * 3) If extra_context is present, it must be followed immediately in
+ * sigcontext.__reserved[] by the terminating null _aarch64_ctx.
+ *
+ * 4) The extra space to which datap points must start at the first
+ * 16-byte aligned address immediately after the terminating null
+ * _aarch64_ctx that follows the extra_context structure in
+ * __reserved[].  The extra space may overrun the end of __reserved[],
+ * as indicated by a sufficiently large value for the size field.
+ *
+ * 5) The extra space must itself be terminated with a null
+ * _aarch64_ctx.
+ */
+#define EXTRA_MAGIC	0x45585401
+
+struct extra_context {
+	struct _aarch64_ctx head;
+	__u64 datap; /* 16-byte aligned pointer to extra space cast to __u64 */
+	__u32 size; /* size in bytes of the extra space */
+	__u32 __reserved[3];
+};
+
 #endif /* _UAPI__ASM_SIGCONTEXT_H */