simpasm: Allow local labels

[hanno-becker]

simpasm simplifies assembly by assembling and disassembling. Global labels are kept and branches adjusted accordingly:

• Global labels 0xDEADBEEF <LABEL>: are detected in the output of objdump --disassemble and replaced by LABEL:.
• References of the form 0xDEADBEEF <LABEL> are detected and replaced by LABEL

This does not work for local labels (.L-prefixed for gcc or L-prefixed for clang). For those, no label will be present in the output of objdump --disassemble, and branches will be relative to surrounding labels, e.g. 0xDEADBEEF <LABEL + 0xCAFFEE>.

Task:
simpasm should use a modified patch_disasm, which works as follows:

• Decode every line in the output of objdump --disassemble into a triple (label, address, instruction) as follows:
  • For a label 0xDEADBEEF <LABEL>, produce the triple (LABEL, None, None). This is essentially decode_label in the current implementation of simpasm.
  • For a line of the form ADDRESS: BYTECODE {INSTRUCTION TEXT}, map it to (None, ADDRESS, INSTRUCTION TEXT)`. This is essentially the regexp after "Drop address and byte code form line"
  • Otherwise, drop the line.
• Then, go through the resulting list of triples, and identify instructions whose instruction text contains relative labels 0xDEADBEEF <LABEL>. In this case, find the instruction with ADDRESS = 0xDEADBEEF in its second component, and add a dummy label FUNCNAME_DEADBEEF in the first component. Replace the 0xDEADBEEF <LABEL> by FUNCNAME_DEADBEEF.
• Finally, produce the assembly by emitting, for each triple (LABEL, ADDRESS, INSTRUCTION TEXT), either INSTRUCTION TEXT if label is None, or LABEL: INSTRUCTION TEXT otherwise.

[hanno-becker]

Not a priority anymore. Closing.