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-rw-r--r--ports/sysdeps/arm/sysdep.h16
1 files changed, 16 insertions, 0 deletions
diff --git a/ports/sysdeps/arm/sysdep.h b/ports/sysdeps/arm/sysdep.h
index 29a78f043d..9230131c78 100644
--- a/ports/sysdeps/arm/sysdep.h
+++ b/ports/sysdeps/arm/sysdep.h
@@ -134,6 +134,22 @@
 	.previous;					\
 99:	OP	R, [pc, T]
 # endif
+
+/* Cope with negative memory offsets, which thumb can't encode.
+   Use NEGOFF_ADJ_BASE to (conditionally) alter the base register,
+   and then NEGOFF_OFF1 to use 0 for thumb and the offset for arm,
+   or NEGOFF_OFF2 to use A-B for thumb and A for arm.  */
+# ifdef __thumb2__
+#  define NEGOFF_ADJ_BASE(R, OFF)	add R, R, $OFF
+#  define NEGOFF_ADJ_BASE2(D, S, OFF)	add D, S, $OFF
+#  define NEGOFF_OFF1(R, OFF)		[R]
+#  define NEGOFF_OFF2(R, OFFA, OFFB)	[R, $((OFFA) - (OFFB))]
+# else
+#  define NEGOFF_ADJ_BASE(R, OFF)
+#  define NEGOFF_ADJ_BASE2(D, S, OFF)	mov D, S
+#  define NEGOFF_OFF1(R, OFF)		[R, $OFF]
+#  define NEGOFF_OFF2(R, OFFA, OFFB)	[R, $OFFA]
+# endif
 #endif	/* __ASSEMBLER__ */
 
 /* This number is the offset from the pc at the current location.  */