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Looking at the ARM disassembler output, every comment seems to start
with a ';' character, so I assumed this was the correct character to
start an assembler comment.
I then spotted a couple of places where there was no ';', but instead,
just a '@' character. I thought that this was a case of a missing
';', and proposed a patch to add the missing ';' characters.
Turns out I was wrong, '@' is actually the ARM assembler comment
character, while ';' is the statement separator. Thus this:
nop ;@ comment
is two statements, the first is the 'nop' instruction, while the
second contains no instructions, just the '@ comment' comment text.
This:
nop @ comment
is a single 'nop' instruction followed by a comment. And finally,
this:
nop ; comment
is two statements, the first contains the 'nop' instruction, while the
second contains the instruction 'comment', which obviously isn't
actually an instruction at all.
Why this matters is that, in the next commit, I would like to add
libopcodes syntax styling support for ARM.
The question then is how should the disassembler style the three cases
above?
As '@' is the actual comment start character then clearly the '@' and
anything after it can be styled as a comment. But what about ';' in
the second example? Style as text? Style as a comment?
And the third example is even harder, what about the 'comment' text?
Style as an instruction mnemonic? Style as text? Style as a comment?
I think the only sensible answer is to move the disassembler to use
'@' consistently as its comment character, and remove all the uses of
';'.
Then, in the next commit, it's obvious what to do.
There's obviously a *lot* of tests that get updated by this commit,
the only actual code changes are in opcodes/arm-dis.c.
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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
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