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linux-user/sh4: Fix crashes on signal delivery
Mikulas Patocka authored 
sh4 uses gUSA (general UserSpace Atomicity) to provide atomicity on CPUs
that don't have atomic instructions. A gUSA region that adds 1 to an
atomic variable stored in @R2 looks like this:

  4004b6:       03 c7           mova    4004c4 <gusa+0x10>,r0
  4004b8:       f3 61           mov     r15,r1
  4004ba:       09 00           nop
  4004bc:       fa ef           mov     #-6,r15
  4004be:       22 63           mov.l   @r2,r3
  4004c0:       01 73           add     #1,r3
  4004c2:       32 22           mov.l   r3,@r2
  4004c4:       13 6f           mov     r1,r15

R0 contains a pointer to the end of the gUSA region
R1 contains the saved stack pointer
R15 contains negative length of the gUSA region

When this region is interrupted by a signal, the kernel detects if
R15 >= -128U. If yes, the kernel rolls back PC to the beginning of the
region and restores SP by copying R1 to R15.

The problem happens if we are interrupted by a signal at address 4004c4.
R15 still holds the value -6, but the atomic value was already written by
an instruction at address 4004c2. In this situation we can't undo the
gUSA. The function unwind_gusa does nothing, the signal handler attempts
to push a signal frame to the address -6 and crashes.

This patch fixes it, so that if we are interrupted at the last instruction
in a gUSA region, we copy R1 to R15 to restore the correct stack pointer
and avoid crashing.

There's another bug: if we are interrupted in a delay slot, we save the
address of the instruction in the delay slot. We must save the address of
the previous instruction.

Cc: qemu-stable@nongnu.org
Signed-off-by: default avatarMikulas Patocka <mpatocka@redhat.com>
Reviewed-by: default avatarYoshinori Sato <ysato@users.sourcefoege.jp>
Message-Id: <b16389f7-6c62-70b7-59b3-87533c0bcc@redhat.com>
Reviewed-by: default avatarRichard Henderson <richard.henderson@linaro.org>
Signed-off-by: default avatarRichard Henderson <richard.henderson@linaro.org>
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ebpf
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gdb-xml
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nbd
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po
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qapi
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qom
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tests
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.editorconfig
.exrc
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.git-blame-ignore-revs
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.gitlab-ci.yml
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COPYING
COPYING.LIB
Kconfig
Kconfig.host
LICENSE
MAINTAINERS
Makefile
README.rst
VERSION
block.c
blockdev-nbd.c
blockdev.c
blockjob.c
configure
cpu-common.c
cpu-target.c
event-loop-base.c
gitdm.config
hmp-commands-info.hx
hmp-commands.hx
iothread.c
job-qmp.c
job.c
memory_ldst.c.inc
meson.build
meson_options.txt
module-common.c
os-posix.c
README.rst

QEMU README

QEMU is a generic and open source machine & userspace emulator and virtualizer.

QEMU is capable of emulating a complete machine in software without any need for hardware virtualization support. By using dynamic translation, it achieves very good performance. QEMU can also integrate with the Xen and KVM hypervisors to provide emulated hardware while allowing the hypervisor to manage the CPU. With hypervisor support, QEMU can achieve near native performance for CPUs. When QEMU emulates CPUs directly it is capable of running operating systems made for one machine (e.g. an ARMv7 board) on a different machine (e.g. an x86_64 PC board).

QEMU is also capable of providing userspace API virtualization for Linux and BSD kernel interfaces. This allows binaries compiled against one architecture ABI (e.g. the Linux PPC64 ABI) to be run on a host using a different architecture ABI (e.g. the Linux x86_64 ABI). This does not involve any hardware emulation, simply CPU and syscall emulation.

QEMU aims to fit into a variety of use cases. It can be invoked directly by users wishing to have full control over its behaviour and settings. It also aims to facilitate integration into higher level management layers, by providing a stable command line interface and monitor API. It is commonly invoked indirectly via the libvirt library when using open source applications such as oVirt, OpenStack and virt-manager.

QEMU as a whole is released under the GNU General Public License, version 2. For full licensing details, consult the LICENSE file.

Documentation

Documentation can be found hosted online at https://www.qemu.org/documentation/. The documentation for the current development version that is available at https://www.qemu.org/docs/master/ is generated from the docs/ folder in the source tree, and is built by Sphinx.

Building

QEMU is multi-platform software intended to be buildable on all modern Linux platforms, OS-X, Win32 (via the Mingw64 toolchain) and a variety of other UNIX targets. The simple steps to build QEMU are:

mkdir build
cd build
../configure
make

Additional information can also be found online via the QEMU website:

Submitting patches

The QEMU source code is maintained under the GIT version control system.

git clone https://gitlab.com/qemu-project/qemu.git

When submitting patches, one common approach is to use 'git format-patch' and/or 'git send-email' to format & send the mail to the qemu-devel@nongnu.org mailing list. All patches submitted must contain a 'Signed-off-by' line from the author. Patches should follow the guidelines set out in the style section of the Developers Guide.

Additional information on submitting patches can be found online via the QEMU website

The QEMU website is also maintained under source control.

git clone https://gitlab.com/qemu-project/qemu-web.git

A 'git-publish' utility was created to make above process less cumbersome, and is highly recommended for making regular contributions, or even just for sending consecutive patch series revisions. It also requires a working 'git send-email' setup, and by default doesn't automate everything, so you may want to go through the above steps manually for once.

For installation instructions, please go to

The workflow with 'git-publish' is:

$ git checkout master -b my-feature
$ # work on new commits, add your 'Signed-off-by' lines to each
$ git publish

Your patch series will be sent and tagged as my-feature-v1 if you need to refer back to it in the future.

Sending v2:

$ git checkout my-feature # same topic branch
$ # making changes to the commits (using 'git rebase', for example)
$ git publish

Your patch series will be sent with 'v2' tag in the subject and the git tip will be tagged as my-feature-v2.

Bug reporting

The QEMU project uses GitLab issues to track bugs. Bugs found when running code built from QEMU git or upstream released sources should be reported via:

If using QEMU via an operating system vendor pre-built binary package, it is preferable to report bugs to the vendor's own bug tracker first. If the bug is also known to affect latest upstream code, it can also be reported via GitLab.

For additional information on bug reporting consult:

ChangeLog

For version history and release notes, please visit https://wiki.qemu.org/ChangeLog/ or look at the git history for more detailed information.

Contact

The QEMU community can be contacted in a number of ways, with the two main methods being email and IRC

Information on additional methods of contacting the community can be found online via the QEMU website: