BL31: Introduce jump primitives

This patch introduces setjmp() and ongjmp() primitives to enable
standard setjmp/longjmp style execution. Both APIs parameters take a
pointer to struct jmpbuf type, which hosts CPU registers saved/restored
during jump.

As per the standard usage:

  - setjmp() return 0 when a jump is setup; and a non-zero value when
    returning from jump.

  - The caller of setjmp() must not return, or otherwise update stack
    pointer since.

Change-Id: I4af1d32e490cfa547979631b762b4cba188d0551
Signed-off-by: Jeenu Viswambharan <jeenu.viswambharan@arm.com>

1 files changed, 59 insertions, 0 deletions

diff --git a/include/lib/aarch64/setjmp.h b/include/lib/aarch64/setjmp.h
new file mode 100644
index 000000000..c65810d82
--- /dev/null
+++ b/include/lib/aarch64/setjmp.h
@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) 2018, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef __JMP_H__
+#define __JMP_H__
+
+#define JMP_CTX_X19	0x0
+#define JMP_CTX_X21	0x10
+#define JMP_CTX_X23	0x20
+#define JMP_CTX_X25	0x30
+#define JMP_CTX_X27	0x40
+#define JMP_CTX_X29	0x50
+#define JMP_CTX_SP	0x60
+#define JMP_CTX_END	0x70
+
+#define JMP_SIZE	(JMP_CTX_END >> 3)
+
+#ifndef __ASSEMBLY__
+
+#include <stdint.h>
+
+/* Jump buffer hosting x18 - x30 and sp_el0 registers */
+struct jmpbuf {
+	uint64_t buf[JMP_SIZE];
+} __aligned(16);
+
+
+/*
+ * Set a jump point, and populate the jump buffer with context information so
+ * that longjmp() can jump later. The caller must adhere to the following
+ * conditions:
+ *
+ *  - After calling this function, the stack must not be shrunk. The contents of
+ *    the stack must not be changed either.
+ *
+ *  - If the caller were to 'return', the buffer must be considered invalid, and
+ *    must not be used with longjmp().
+ *
+ * The caller will observe this function returning at two distinct
+ * circumstances, each with different return values:
+ *
+ *  - Zero, when the buffer is setup;
+ *
+ *  - Non-zero, when a call to longjmp() is made (presumably by one of the
+ *    callee functions) with the same jump buffer.
+ */
+int setjmp(struct jmpbuf *buf);
+
+/*
+ * Reset execution to a jump point, and restore context information according to
+ * the jump buffer populated by setjmp().
+ */
+void longjmp(struct jmpbuf *buf);
+
+#endif /* __ASSEMBLY__ */
+#endif /* __JMP_H__ */