fix relative jumps for immediate offsets

The JUMPR and JUMPS instructions in assembly are defined to take
an offset in bytes, but the real CPU instruction expects this to
be expressed in 32-bit words. Thus, the assembler needs to
translate offsets into words (32-bits). i.e. 4 bytes is 1 word.

Only immediate values, which are multiples of 4 are allowed. Other
values will result in a ValueError. (binutils-esp32ulp actually
allows other values and rounds the result, but to get the exact same
behaviour as binutils with its peculiarities would require a bigger
change for a case, which might more likely represent a mistake than
a useful offset)

Note, since py-esp32-ulp already tracks label offsets in 32-bit words
internally, this conversion is only necessary for immediate offsets.

Author: wnienhaus

Diff for: esp32_ulp/opcodes.py

@@ -340,7 +340,9 @@ def get_rel(arg):
     if isinstance(arg, str):
         arg = arg_qualify(arg)
     if arg.type == IMM:
-        return arg.value
+        if arg.value & 3 != 0:  # bitwise version of: arg.value % 4 != 0
+            raise ValueError('Relative offset must be a multiple of 4')
+        return arg.value >> 2  # bitwise version of: arg.value // 4
     if arg.type == SYM:
         return symbols.resolve_relative(arg.value)
     raise TypeError('wanted: immediate, got: %s' % arg.raw)

Diff for: tests/compat/jumps.S

@@ -3,6 +3,7 @@
 entry:
   nop
 
+  # jumps with labels
   jumps entry, 42, lt
   jumps entry, 42, lt
   jumps later, 42, lt
@@ -15,6 +16,18 @@ entry:
   jumps entry, 42, gt
   jumps later, 42, gt
 
+  # jumps with immediate offset (specified in bytes, but real instruction uses words)
+  jumps 0, 42, lt
+
+  jumps 4, 42, lt
+  jumps 8, 42, lt
+  jumps 32, 42, lt
+
+  jumps -4, 42, lt
+  jumps -8, 42, lt
+  jumps -32, 42, lt
+
+  # jumpr with labels
   jumpr entry, 42, lt
   jumpr later, 42, lt
   jumpr entry, 42, ge
@@ -26,6 +39,17 @@ entry:
   jumpr entry, 42, eq
   jumpr later, 42, eq
 
+  # jumpr with immediate offset (specified in bytes, but real instruction uses words)
+  jumpr 0, 42, lt
+
+  jumpr 4, 42, lt
+  jumpr 8, 42, lt
+  jumpr 32, 42, lt
+
+  jumpr -4, 42, lt
+  jumpr -8, 42, lt
+  jumpr -32, 42, lt
+
   nop
   nop
   nop