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Date: Thu, 28 Sep 2017 15:37:04 +0100 From: Dave Martin <Dave.Martin@....com> To: Will Deacon <will.deacon@....com> Cc: mmarek@...e.cz, akpm@...ux-foundation.org, linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org Subject: Re: [PATCH] scripts/decodecode: Fix decoding for AArch64 (arm64) instructions 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). > > > 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@....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. Fair enough. I suspected as much, too. Cheers ---Dave > > > + 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@....com> > > Thanks! > > Will > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@...ts.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
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