Fix shifting of negative value

When UBSan is enabled, I noticed runtime errors complaining of shifting
of negative numbers.

This patch fixes this by reusing existing macros from the ARM port.

It also removes unused macros from AArch64's port.

gdb/ChangeLog:

2020-12-04  Luis Machado  <luis.machado@linaro.org>

	* aarch64-tdep.c (submask, bit, bits): Remove.
	* arch/aarch64-insn.c (extract_signed_bitfield): Remove.
	(aarch64_decode_adr, aarch64_decode_b aarch64_decode_bcond)
	(aarch64_decode_cb, aarch64_decode_tb)
	(aarch64_decode_ldr_literal): Use sbits to extract a signed
	immediate.
	* arch/aarch64-insn.h (submask, bits, bit, sbits): New macros.

1 files changed, 16 insertions, 0 deletions

diff --git a/gdb/arch/aarch64-insn.h b/gdb/arch/aarch64-insn.h
index 6a63ce9..5ce46c1 100644
--- a/gdb/arch/aarch64-insn.h
+++ b/gdb/arch/aarch64-insn.h
@@ -21,6 +21,22 @@
 
 extern bool aarch64_debug;
 
+/* Support routines for instruction parsing.  */
+
+/* Create a mask of X bits.  */
+#define submask(x) ((1L << ((x) + 1)) - 1)
+
+/* Extract the bitfield from OBJ starting at bit ST and ending at bit FN.  */
+#define bits(obj,st,fn) (((obj) >> (st)) & submask ((fn) - (st)))
+
+/* Extract bit ST from OBJ.  */
+#define bit(obj,st) (((obj) >> (st)) & 1)
+
+/* Extract the signed bitfield from OBJ starting at bit ST and ending at
+   bit FN.  The result is sign-extended.  */
+#define sbits(obj,st,fn) \
+  ((long) (bits(obj,st,fn) | ((long) bit(obj,fn) * ~ submask (fn - st))))
+
 /* List of opcodes that we need for building the jump pad and relocating
    an instruction.  */