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SubjectRe: [PATCH] scripts/decodecode: Fix decoding for AArch64 (arm64) instructions
On Thu, Sep 28, 2017 at 01:42:31PM +0100, Dave Martin wrote:
> On Thu, Sep 28, 2017 at 11:55:47AM +0100, Will Deacon wrote:
> > There are a couple of problems with the decodecode script and arm64:
> >
> > 1. AArch64 objdump refuses to disassemble .4byte directives as instructions,
> > insisting that they are data values and displaying them as:
> >
> > a94153f3 .word 0xa94153f3 <-- trapping instruction
> >
> > This is resolved by using the .inst directive instead.
> >
> > 2. Disassembly of branch instructions attempts to provide the target as
> > an offset from a symbol, e.g.:
> >
> > 0: 34000082 cbz w2, 10 <.text+0x10>
> >
> > however this falls foul of the grep -v, which matches lines containing
> > ".text" and ends up removing all branch instructions from the dump.
>
> Any idea why this doesn't affect other arches too ... or does it?

I'm not sure, although I don't know how .inst works for architectures
with variable-length instructions and I *guess* the disassembly is less
fussy about data vs text for those targets.

> > This patch resolves both issues by using the .inst directive for 4-byte
> > quantities on arm64 and stripping the resulting binaries (as is done on
> > arm already) to remove the mapping symbols.
> >
> > Signed-off-by: Will Deacon <will.deacon@arm.com>
> >
> > ---
> > scripts/decodecode | 8 ++++++++
> > 1 file changed, 8 insertions(+)
> >
> > diff --git a/scripts/decodecode b/scripts/decodecode
> > index d8824f37acce..67214ec5b2cb 100755
> > --- a/scripts/decodecode
> > +++ b/scripts/decodecode
> > @@ -58,6 +58,14 @@ disas() {
> > ${CROSS_COMPILE}strip $1.o
> > fi
> >
> > + if [ "$ARCH" = "arm64" ]; then
> > + if [ $width -eq 4 ]; then
> > + type=inst
>
> Can we merge with arm here, or does arm still support toolchains that
> don't have .inst? Anyway, no big deal.

I thought we still supported those, so I'd be reluctant to merge the
clauses unless it's broken (the script works as-is for me with arm). I'm
also not sure what we should do for 16-bit Thumb-2 encodings, where we
have inst.n and inst.w to contend with.

> > + fi
> > +
> > + ${CROSS_COMPILE}strip $1.o
> > + fi
> > +
> > ${CROSS_COMPILE}objdump $OBJDUMPFLAGS -S $1.o | \
> > grep -v "/tmp\|Disassembly\|\.text\|^$" > $1.dis 2>&1
>
> FWIW,
>
> Reviewed-by: Dave Martin <Dave.Martin@arm.com>

Thanks!

Will

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