[ARM] Add support for thumb1 pcrop relocations.

To support thumb1 execute-only code we need to support four new
relocations (R_ARM_THM_ALU_ABS_G0_NC, R_ARM_THM_ALU_ABS_G1_NC,
R_ARM_THM_ALU_ABS_G2_NC and  R_ARM_THM_ALU_ABS_G3_NC).
These relocations allow the static linker to finalize construction
of symbol address.
Typical sequence of code to get address of the symbol foo is then
the following :
	movs	r3, #:upper8_15:#foo
	lsls	r3, #8
	adds	r3, #:upper0_7:#foo
	lsls	r3, #8
	adds	r3, #:lower8_15:#foo
	lsls	r3, #8
	adds	r3, #:lower0_7:#foo
This will give following sequence of text and relocations after
assembly :
   4:	2300      	movs	r3, #0
			4: R_ARM_THM_ALU_ABS_G3_NC	foo
   6:	021b      	lsls	r3, r3, #8
   8:	3300      	adds	r3, #0
			8: R_ARM_THM_ALU_ABS_G2_NC	foo
   a:	021b      	lsls	r3, r3, #8
   c:	3300      	adds	r3, #0
			c: R_ARM_THM_ALU_ABS_G1_NC	foo
   e:	021b      	lsls	r3, r3, #8
  10:	3300      	adds	r3, #0
			10: R_ARM_THM_ALU_ABS_G0_NC	foo

1 files changed, 16 insertions, 0 deletions

diff --git a/gas/doc/c-arm.texi b/gas/doc/c-arm.texi
index ee26e6d..091fc93 100644
--- a/gas/doc/c-arm.texi
+++ b/gas/doc/c-arm.texi
@@ -537,6 +537,22 @@ respectively.  For example to load the 32-bit address of foo into r0:
         MOVT r0, #:upper16:foo
 @end smallexample
 
+Relocations @samp{R_ARM_THM_ALU_ABS_G0_NC}, @samp{R_ARM_THM_ALU_ABS_G1_NC},
+@samp{R_ARM_THM_ALU_ABS_G2_NC} and @samp{R_ARM_THM_ALU_ABS_G3_NC} can be
+generated by prefixing the value with @samp{#:lower0_7:#},
+@samp{#:lower8_15:#}, @samp{#:upper0_7:#} and @samp{#:upper8_15:#}
+respectively.  For example to load the 32-bit address of foo into r0:
+
+@smallexample
+        MOVS r0, #:upper8_15:#foo
+        LSLS r0, r0, #8
+        ADDS r0, #:upper0_7:#foo
+        LSLS r0, r0, #8
+        ADDS r0, #:lower8_15:#foo
+        LSLS r0, r0, #8
+        ADDS r0, #:lower0_7:#foo
+@end smallexample
+
 @node ARM-Neon-Alignment
 @subsection NEON Alignment Specifiers