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SubjectRe: [PATCH] scripts/decodecode: Fix decoding for AArch64 (arm64) instructions
On Thu, Sep 28, 2017 at 07:01:35PM +0100, Will Deacon wrote:
> On Thu, Sep 28, 2017 at 03:37:04PM +0100, Dave Martin wrote:
> > On Thu, Sep 28, 2017 at 03:14:47PM +0100, Will Deacon wrote:
> > > 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.
> >
> > I rather meant the target disassembly for relative branches in the
> > absence of labels.
> >
> > Anyway, I think this is at least harmless to other arches, and possibly
> > helpful to them (if they disassemble those branch targets in the same
> > sort of way).
>
> Ah, I see what you mean. Something like the fixup below on top.
>
> Will
>
> --->8
>
> diff --git a/scripts/decodecode b/scripts/decodecode
> index 67214ec5b2cb..f1ec57c3cbf7 100755
> --- a/scripts/decodecode
> +++ b/scripts/decodecode
> @@ -49,21 +49,14 @@ esac
>
> disas() {
> ${CROSS_COMPILE}as $AFLAGS -o $1.o $1.s > /dev/null 2>&1
> + ${CROSS_COMPILE}strip $1.o
>
> - if [ "$ARCH" = "arm" ]; then
> - if [ $width -eq 2 ]; then
> - OBJDUMPFLAGS="-M force-thumb"
> - fi
> -
> - ${CROSS_COMPILE}strip $1.o
> + if [ "$ARCH" = "arm" -a $width -eq 2 ]; then
> + OBJDUMPFLAGS="-M force-thumb"
> fi
>
> - if [ "$ARCH" = "arm64" ]; then
> - if [ $width -eq 4 ]; then
> - type=inst
> - fi
> -
> - ${CROSS_COMPILE}strip $1.o
> + if [ "$ARCH" = "arm64" -a $width -eq 4 ]; then
> + type=inst
> fi

Reasonable, though I guess it doesn't matter unless another arch really
cares -- in which case someone will eventually spot the issue and
probably write the same patch.

Cheers
---Dave

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