Re: [PATCH] qemu-options.hx: Document -M as -machine alias

["Dr. David Alan Gilbert" <dave@treblig.org>]

* Peter Maydell (peter.maydell@linaro.org) wrote:
> On Wed, 3 Dec 2025 at 14:00, Dr. David Alan Gilbert <dave@treblig.org> wrote:
> >
> > * Alex Bennée (alex.bennee@linaro.org) wrote:
> > > dave@treblig.org writes:
> > >
> > > > From: "Dr. David Alan Gilbert" <dave@treblig.org>
> > > >
> > > > -M is used heavily in documentation and scripts, but isn't actually
> > > > documented anywhere.
> > > > Document it as equivalent to -machine.
> > > >
> > > > Reported-by: Julian Andres Klode <jak@jak-linux.org>
> > > > Signed-off-by: Dr. David Alan Gilbert <dave@treblig.org>
> > > > ---
> > > >  qemu-options.hx | 12 +++++++-----
> > > >  1 file changed, 7 insertions(+), 5 deletions(-)
> > > >
> > > > diff --git a/qemu-options.hx b/qemu-options.hx
> > > > index fca2b7bc74..ec92723f10 100644
> > > > --- a/qemu-options.hx
> > > > +++ b/qemu-options.hx
> > > > @@ -44,6 +44,7 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \
> > > >  #endif
> > > >      "                memory-backend='backend-id' specifies explicitly provided backend for main RAM (default=none)\n"
> > > >      "                cxl-fmw.0.targets.0=firsttarget,cxl-fmw.0.targets.1=secondtarget,cxl-fmw.0.size=size[,cxl-fmw.0.interleave-granularity=granularity]\n"
> > > > +    "                sgx-epc.0.memdev=memid,sgx-epc.0.node=numaid\n"
> > > >      "                smp-cache.0.cache=cachename,smp-cache.0.topology=topologylevel\n",
> > > >      QEMU_ARCH_ALL)
> > > >  SRST
> > > > @@ -179,6 +180,9 @@ SRST
> > > >
> > > >              -machine cxl-fmw.0.targets.0=cxl.0,cxl-fmw.0.targets.1=cxl.1,cxl-fmw.0.size=128G,cxl-fmw.0.interleave-granularity=512
> > > >
> > > > +    ``sgx-epc.0.memdev=@var{memid},sgx-epc.0.node=@var{numaid}``
> > > > +        Define an SGX EPC section.
> > > > +
> > >
> > > This seems unrelated.
> > >
> > > >      ``smp-cache.0.cache=cachename,smp-cache.0.topology=topologylevel``
> > > >          Define cache properties for SMP system.
> > > >
> > > > @@ -208,12 +212,10 @@ SRST
> > > >  ERST
> > > >
> > > >  DEF("M", HAS_ARG, QEMU_OPTION_M,
> > > > -    "                sgx-epc.0.memdev=memid,sgx-epc.0.node=numaid\n",
> > > > -    QEMU_ARCH_ALL)
> > > > -
> > > > +    "-M              as -machine\n", QEMU_ARCH_ALL)
> > > >  SRST
> > > > -``sgx-epc.0.memdev=@var{memid},sgx-epc.0.node=@var{numaid}``
> > > > -    Define an SGX EPC section.
> > > > +``-M``
> > > > +    as -machine.
> 
> Surprisingly, this and -h/--help are our only two options where
> we provide a short synonym. I note that this handling of -M
> is not consistent with how we document -h/--help, where we
> print both on a single line:
> -h or -help     display this help and exit
> 
> But it would be trickier to fit that in for -machine and
> perhaps confusing given the suboptions.

Right, that's one of the two reasons I kept it separate.
The other reason, is that I couldn't figure out how '-help' and '-h'
both got defined - why is the second DEF(...) not needed?

> > > Did we have a merge conflict at some point that messed things up?
> >
> > It's not clear - it was the only option hanging around in -M and it was
> > already appearing wrong in the man output.
> > I wondered if it was some requirement to have *something* in the -M
> > definition so thought it best to move it at the same time.
> 
> It looks like this was incorrectly added under -M by
> commit dfce81f1b9 ("vl: Add sgx compound properties to expose
> SGX EPC sections to guest"), which should have put it under
> -machine like all our other machine suboption documentation.
> 
> The result is that the sgx-epc documentation appears OK
> in --help because the --help output just concatenates
> everything so it gets tacked on after the -machine help,
> but it is misrendered in the HTML docs:
> https://qemu-project.gitlab.io/qemu/system/invocation.html
> as it appears as if a top level option rather than one
> indented to indicate that it's a machine sub-option.
> So this change fixes that bug (and should ideally say so
> in its commit message).
> 
> Before that it simply read
> -HXCOMM Deprecated by -machine
> -DEF("M", HAS_ARG, QEMU_OPTION_M, "", QEMU_ARCH_ALL)
> 
> (Commit dfce81f1b9 also silently dropped that "deprecated"
> comment, which it shouldn't really have done.)

Ah.

Dave

> thanks
> -- PMM
-- 
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