Merge remote-tracking branch 'remotes/bonzini-gitlab/tags/for-upstream' into staging

* Reverse debugging (Pavel)
* CFLAGS cleanup (Paolo)
* ASLR fix (Mark)
* cpus.c refactoring (Claudio)

# gpg: Signature made Tue 06 Oct 2020 07:35:09 BST
# gpg:                using RSA key F13338574B662389866C7682BFFBD25F78C7AE83
# gpg:                issuer "pbonzini@redhat.com"
# gpg: Good signature from "Paolo Bonzini <bonzini@gnu.org>" [full]
# gpg:                 aka "Paolo Bonzini <pbonzini@redhat.com>" [full]
# Primary key fingerprint: 46F5 9FBD 57D6 12E7 BFD4  E2F7 7E15 100C CD36 69B1
#      Subkey fingerprint: F133 3857 4B66 2389 866C  7682 BFFB D25F 78C7 AE83

* remotes/bonzini-gitlab/tags/for-upstream: (37 commits)
  tests/acceptance: add reverse debugging test
  replay: create temporary snapshot at debugger connection
  replay: describe reverse debugging in docs/replay.txt
  gdbstub: add reverse continue support in replay mode
  gdbstub: add reverse step support in replay mode
  replay: flush rr queue before loading the vmstate
  replay: implement replay-seek command
  replay: introduce breakpoint at the specified step
  replay: introduce info hmp/qmp command
  qapi: introduce replay.json for record/replay-related stuff
  migration: introduce icount field for snapshots
  qcow2: introduce icount field for snapshots
  replay: provide an accessor for rr filename
  replay: don't record interrupt poll
  configure: don't enable ASLR for --enable-debug Windows builds
  configure: consistently pass CFLAGS/CXXFLAGS/LDFLAGS to meson
  configure: do not clobber environment CFLAGS/CXXFLAGS/LDFLAGS
  dtc: Convert Makefile bits to meson bits
  slirp: Convert Makefile bits to meson bits
  accel/tcg: use current_machine as it is always set for softmmu
  ...

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

2 files changed, 54 insertions, 3 deletions

diff --git a/docs/interop/qcow2.txt b/docs/interop/qcow2.txt
index 7da0d81..0463f76 100644
--- a/docs/interop/qcow2.txt
+++ b/docs/interop/qcow2.txt
@@ -707,6 +707,11 @@ Snapshot table entry:
 
                     Byte 48 - 55:   Virtual disk size of the snapshot in bytes
 
+                    Byte 56 - 63:   icount value which corresponds to
+                                    the record/replay instruction count
+                                    when the snapshot was taken. Set to -1
+                                    if icount was disabled
+
                     Version 3 images must include extra data at least up to
                     byte 55.
 
diff --git a/docs/replay.txt b/docs/replay.txt
index 70c27ed..87a64ae 100644
--- a/docs/replay.txt
+++ b/docs/replay.txt
@@ -184,11 +184,11 @@ is then incremented (which is called "warping" the virtual clock) as
 soon as the timer fires or the CPUs need to go out of the idle state.
 Two functions are used for this purpose; because these actions change
 virtual machine state and must be deterministic, each of them creates a
-checkpoint.  qemu_start_warp_timer checks if the CPUs are idle and if so
-starts accounting real time to virtual clock.  qemu_account_warp_timer
+checkpoint.  icount_start_warp_timer checks if the CPUs are idle and if so
+starts accounting real time to virtual clock.  icount_account_warp_timer
 is called when the CPUs get an interrupt or when the warp timer fires,
 and it warps the virtual clock by the amount of real time that has passed
-since qemu_start_warp_timer.
+since icount_start_warp_timer.
 
 Bottom halves
 -------------
@@ -265,6 +265,16 @@ of the original disk image, use overlay files linked to the original images.
 Therefore all new snapshots (including the starting one) will be saved in
 overlays and the original image remains unchanged.
 
+When you need to use snapshots with diskless virtual machine,
+it must be started with 'orphan' qcow2 image. This image will be used
+for storing VM snapshots. Here is the example of the command line for this:
+
+  qemu-system-i386 -icount shift=3,rr=replay,rrfile=record.bin,rrsnapshot=init \
+    -net none -drive file=empty.qcow2,if=none,id=rr
+
+empty.qcow2 drive does not connected to any virtual block device and used
+for VM snapshots only.
+
 Network devices
 ---------------
 
@@ -294,6 +304,42 @@ for recording and replaying must contain identical number of ports in record
 and replay modes, but their backends may differ.
 E.g., '-serial stdio' in record mode, and '-serial null' in replay mode.
 
+Reverse debugging
+-----------------
+
+Reverse debugging allows "executing" the program in reverse direction.
+GDB remote protocol supports "reverse step" and "reverse continue"
+commands. The first one steps single instruction backwards in time,
+and the second one finds the last breakpoint in the past.
+
+Recorded executions may be used to enable reverse debugging. QEMU can't
+execute the code in backwards direction, but can load a snapshot and
+replay forward to find the desired position or breakpoint.
+
+The following GDB commands are supported:
+ - reverse-stepi (or rsi) - step one instruction backwards
+ - reverse-continue (or rc) - find last breakpoint in the past
+
+Reverse step loads the nearest snapshot and replays the execution until
+the required instruction is met.
+
+Reverse continue may include several passes of examining the execution
+between the snapshots. Each of the passes include the following steps:
+ 1. loading the snapshot
+ 2. replaying to examine the breakpoints
+ 3. if breakpoint or watchpoint was met
+    - loading the snaphot again
+    - replaying to the required breakpoint
+ 4. else
+    - proceeding to the p.1 with the earlier snapshot
+
+Therefore usage of the reverse debugging requires at least one snapshot
+created in advance. This can be done by omitting 'snapshot' option
+for the block drives and adding 'rrsnapshot' for both record and replay
+command lines.
+See the "Snapshotting" section to learn more about running record/replay
+and creating the snapshot in these modes.
+
 Replay log format
 -----------------