------- Additional Comments From nickc at redhat dot com 2009-06-12 12:22
-------
Subject: Re: New: objdump does not disassemble ARM code
entered with .word directives
Hi Mike,
> It used to be possible to enter instructions with .word directives and then
> disassemble them with objdump -d, but that no longer works. Example:
> mov r0, r1
> .word 0xe1a00001
> bx lr
> 0: e1a00001 mov r0, r1
> 4: e1a00001 .word 0xe1a00001
> 8: e12fff1e bx lr
This is actually the intended behaviour. The .word directive is used to
enter data not instructions and the ARM port of GAS makes a note of this
by emitting a local mapping symbol. For example if you run:
armv5tel-unknown-linux-gnueabi-readelf --syms test.o
You will see:
Symbol table '.symtab' contains 9 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 00000000 0 NOTYPE LOCAL DEFAULT UND
1: 00000000 0 SECTION LOCAL DEFAULT 1
2: 00000000 0 SECTION LOCAL DEFAULT 3
3: 00000000 0 SECTION LOCAL DEFAULT 4
4: 00000000 0 NOTYPE LOCAL DEFAULT 1 $a
5: 00000004 0 NOTYPE LOCAL DEFAULT 1 $d
6: 00000008 0 NOTYPE LOCAL DEFAULT 1 $a
It is the $d symbol, entry number 5 in the symbol table, which is
telling the disassemble that the word at 0x00000004 is not an
instruction but data and so it should not attempt to disassemble it.
It would be possible to add a new pseudo-op, say ".insn", to insert a
numeric value into the output and have it be labelled as in instruction,
but why bother ? Do you really need this functionality. Why not just
assemble the instruction normally ?
Cheers
Nick
--
http://sourceware.org/bugzilla/show_bug.cgi?id=10263
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