have sections aligned at / end at 32bit boundaries

Author: ThomasWaldmann

demo.S

@@ -54,12 +54,12 @@ textend:
 data0:      .skip 4, 0x23
 data1:      .space 4, 0x42
 data2:      .skip 4
-datab:      .byte 1, 2, 3, 4
 dataw:      .word 1, 2, 3, 4
 datal:      .long 1, 2, 3, 4
+datab:      .byte 1, 2, 3  # test alignment / fill up of section
 dataend:
 
             .bss
 bss0:       .skip 4
-bss1:       .skip 2
+bss1:       .skip 2  # test alignment / fill up of section
 bssend:

esp32_ulp/assemble.py

@@ -65,6 +65,18 @@ def append_section(self, value, expected_section=None):
             self.sections[s].append(value)
             self.offsets[s] += len(value)
 
+    def finalize_sections(self):
+        # make sure all sections have a bytelength dividable by 4,
+        # thus having all sections aligned at 32bit-word boundaries.
+        for s in list(self.sections.keys()) + [BSS, ]:
+            offs = self.offsets[s]
+            mod = offs % 4
+            if mod:
+                fill = int(0).to_bytes(4 - mod, 'little')
+                self.offsets[s] += len(fill)
+                if s is not BSS:
+                    self.sections[s].append(fill)
+
     def dump(self):
         print("Symbols:")
         for label, section_offset in sorted(self.symbols.items()):
@@ -144,4 +156,5 @@ def assemble(self, lines):
                         self.append_section(instruction.to_bytes(4, 'little'), TEXT)
                         continue
                 raise Exception('Unknown opcode or directive: %s' % opcode)
+        self.finalize_sections()