On Wed, 22 Jun 2022 at 15:53, Alex Bennée <alex.ben...@linaro.org> wrote: > > How to control the booting of QEMU is often a source of confusion for > users. Bring the options that control this together in the manual > pages and add some verbiage to describe when each option is > appropriate.
https://stackoverflow.com/a/58434837/4499941 is my answer to this common user question, though it's a bit more conversational in tone than we want for the manual :-) > Signed-off-by: Alex Bennée <alex.ben...@linaro.org> > Cc: Cédric Le Goater <c...@kaod.org> > --- > qemu-options.hx | 80 ++++++++++++++++++++++++++++++++++++++----------- > 1 file changed, 62 insertions(+), 18 deletions(-) > > diff --git a/qemu-options.hx b/qemu-options.hx > index 377d22fbd8..9b0242f0ef 100644 > --- a/qemu-options.hx > +++ b/qemu-options.hx > @@ -1585,13 +1585,6 @@ SRST > Use file as SecureDigital card image. > ERST > > -DEF("pflash", HAS_ARG, QEMU_OPTION_pflash, > - "-pflash file use 'file' as a parallel flash image\n", QEMU_ARCH_ALL) > -SRST > -``-pflash file`` > - Use file as a parallel flash image. > -ERST > - > DEF("snapshot", 0, QEMU_OPTION_snapshot, > "-snapshot write to temporary files instead of disk image files\n", > QEMU_ARCH_ALL) > @@ -3680,12 +3673,51 @@ DEFHEADING() > > #endif > > -DEFHEADING(Linux/Multiboot boot specific:) > +DEFHEADING(Boot Image or Kernel specific:) > +SRST > +There are broadly 4 ways you can boot a system with QEMU. > + > + - specify a firmware and let it control finding a kernel > + - specify a firmware and pass a hint to the kernel to boot > + - direct kernel image boot > + - manually load files into the guests address space "guest's" > + > +The last method Do you mean the third method? The last method isn't usually used to load kernels, but rather bare-metal binaries. is useful for quickly testing kernels but as there is > +no firmware to pass configuration information to the kernel it must > +either be built for the exact configuration or be handed a DTB blob > +which tells the kernel what drivers it needs. This is all somewhat architecture specific: you don't necessarily need to do either of those if the hardware is probeable. You should also mention that all of this is board specific. > + > +ERST > + > +SRST > + > +For x86 machines ``-bios`` will generally do the right thing with > +whatever it is given. For non-x86 machines the more strict ``-pflash`` > +option needs an image that is sized for the flash device for the given > +machine type. -bios works for some non-x86 machine types too. Ideally we would: * have all our machine types have some documentation * have the documentation for each machine type say whether it supports -bios or not, and what it does > + > +ERST > + > +DEF("bios", HAS_ARG, QEMU_OPTION_bios, \ > + "-bios file set the filename for the BIOS\n", QEMU_ARCH_ALL) > +SRST > +``-bios file`` > + Set the filename for the BIOS. > +ERST > + > +DEF("pflash", HAS_ARG, QEMU_OPTION_pflash, > + "-pflash file use 'file' as a parallel flash image\n", QEMU_ARCH_ALL) > +SRST > +``-pflash file`` > + Use file as a parallel flash image. > +ERST > + > SRST > -When using these options, you can use a given Linux or Multiboot kernel > -without installing it in the disk image. It can be useful for easier > -testing of various kernels. > > +The kernel options were designed to work with Linux kernels although > +other things (like hypervisors) can be packaged up as a kernel > +executable image. The exact format of a executable image is usually > +architecture specific. > > ERST > > @@ -3725,6 +3757,25 @@ SRST > kernel on boot. > ERST > > +SRST > + > +Finally you can also manually load images directly into the address > +space of the guest. This is most useful for developers who already > +know the layout of their guest and take care to ensure something sane > +will happen when the reset vector executes. We should say that this is the favoured option for "I want to run a bare-metal binary", and we should also say that this option works the same way on any architecture and machine. > + > +The generic loader can be invoked by using the loader device: > + > +``-device > loader,addr=<addr>,data=<data>,data-len=<data-len>[,data-be=<data-be>][,cpu-num=<cpu-num>]`` > + > +there is also the guest loader which operates in a similar way but > +tweaks the DTB so a hypervisor loaded via ``-kernel`` can find where > +the guest image is: > + > +``-device > guest-loader,addr=<addr>[,kernel=<path>,[bootargs=<arguments>]][,initrd=<path>]`` > + > +ERST > + > DEFHEADING() thanks -- PMM
