The v8M architecture includes hardware support for enforcing
stack pointer limits. We don't implement this behaviour yet,
but provide the MSPLIM and PSPLIM stack pointer limit registers
as reads-as-written, so that when we do implement the checks
in future this won't break guest migration.
Backports commit 57bb31568114023f67680d6fe478ceb13c51aa7d from qemu
We were previously making the system control register (SCR)
just RAZ/WI. Although we don't implement the functionality
this register controls, we should at least provide the state,
including the banked state for v8M.
Backports register related changes in commit 24ac0fb129f9ce9dd96901b2377fc6271dc55b2b from qemu
M profile cores have a similar setup for cache ID registers
to A profile:
* Cache Level ID Register (CLIDR) is a fixed value
* Cache Type Register (CTR) is a fixed value
* Cache Size ID Registers (CCSIDR) are a bank of registers;
which one you see is selected by the Cache Size Selection
Register (CSSELR)
The only difference is that they're in the NVIC memory mapped
register space rather than being coprocessor registers.
Implement the M profile view of them.
Since neither Cortex-M3 nor Cortex-M4 implement caches,
we don't need to update their init functions and can leave
the ctr/clidr/ccsidr[] fields in their ARMCPU structs at zero.
Newer cores (like the Cortex-M33) will want to be able to
set these ID registers to non-zero values, though.
Backports commit 43bbce7fbef22adf687dd84934fd0b2f8df807a8 from qemu
Change vfp.regs as a uint64_t to vfp.zregs as an ARMVectorReg.
The previous patches have made the change in representation
relatively painless.
Backports commit c39c2b9043ec59516c80f2c6f3e8193e99d04d4b from qemu
This implements emulation of the new SM4 instructions that have
been added as an optional extension to the ARMv8 Crypto Extensions
in ARM v8.2.
Backports commit b6577bcd251ca0d57ae1de149e3c706b38f21587 from qemu
This implements emulation of the new SM3 instructions that have
been added as an optional extension to the ARMv8 Crypto Extensions
in ARM v8.2.
Backports commit 80d6f4c6bbb718f343a832df8dee15329cc7686c from qemu
This implements emulation of the new SHA-512 instructions that have
been added as an optional extensions to the ARMv8 Crypto Extensions
in ARM v8.2.
Backports commit 90b827d131812d7f0a8abb13dba1942a2bcee821 from qemu
The Application Interrupt and Reset Control Register has some changes
for v8M:
* new bits SYSRESETREQS, BFHFNMINS and PRIS: these all have
real state if the security extension is implemented and otherwise
are constant
* the PRIGROUP field is banked between security states
* non-secure code can be blocked from using the SYSRESET bit
to reset the system if SYSRESETREQS is set
Implement the new state and the changes to register read and write.
For the moment we ignore the effects of the secure PRIGROUP.
We will implement the effects of PRIS and BFHFNMIS later.
Backports register-related additions in commit 3b2e934463121f06d04e4d17658a9a7cdc3717b0 from qemu
Currently armv7m_nvic_acknowledge_irq() does three things:
* make the current highest priority pending interrupt active
* return a bool indicating whether that interrupt is targeting
Secure or NonSecure state
* implicitly tell the caller which is the highest priority
pending interrupt by setting env->v7m.exception
We need to split these jobs, because v7m_exception_taken()
needs to know whether the pending interrupt targets Secure so
it can choose to stack callee-saves registers or not, but it
must not make the interrupt active until after it has done
that stacking, in case the stacking causes a derived exception.
Similarly, it needs to know the number of the pending interrupt
so it can read the correct vector table entry before the
interrupt is made active, because vector table reads might
also cause a derived exception.
Create a new armv7m_nvic_get_pending_irq_info() function which simply
returns information about the highest priority pending interrupt, and
use it to rearrange the v7m_exception_taken() code so we don't
acknowledge the exception until we've done all the things which could
possibly cause a derived exception.
Backports part of commit 6c9485188170e11ad31ce477c8ce200b8e8ce59d from qemu
In order to support derived exceptions (exceptions generated in
the course of trying to take an exception), we need to be able
to handle prioritizing whether to take the original exception
or the derived exception.
We do this by introducing a new function
armv7m_nvic_set_pending_derived() which the exception-taking code in
helper.c will call when a derived exception occurs. Derived
exceptions are dealt with mostly like normal pending exceptions, so
we share the implementation with the armv7m_nvic_set_pending()
function.
Note that the way we structure this is significantly different
from the v8M Arm ARM pseudocode: that does all the prioritization
logic in the DerivedLateArrival() function, whereas we choose to
let the existing "identify highest priority exception" logic
do the prioritization for us. The effect is the same, though.
Backports part of commit 5ede82b8ccb652382c106d53f656ed67997d76e8 from qemu
The TT instruction is going to need to look up the MMU index
for a specified security and privilege state. Refactor the
existing arm_v7m_mmu_idx_for_secstate() into a version that
lets you specify the privilege state and one that uses the
current state of the CPU.
Backports commit ec8e3340286a87d3924c223d60ba5c994549f796 from qemu
For M profile, we currently have an mmu index MNegPri for
"requested execution priority negative". This fails to
distinguish "requested execution priority negative, privileged"
from "requested execution priority negative, usermode", but
the two can return different results for MPU lookups. Fix this
by splitting MNegPri into MNegPriPriv and MNegPriUser, and
similarly for the Secure equivalent MSNegPri.
This takes us from 6 M profile MMU modes to 8, which means
we need to bump NB_MMU_MODES; this is OK since the point
where we are forced to reduce TLB sizes is 9 MMU modes.
(It would in theory be possible to stick with 6 MMU indexes:
{mpu-disabled,user,privileged} x {secure,nonsecure} since
in the MPU-disabled case the result of an MPU lookup is
always the same for both user and privileged code. However
we would then need to rework the TB flags handling to put
user/priv into the TB flags separately from the mmuidx.
Adding an extra couple of mmu indexes is simpler.)
Backports commit 62593718d77c06ad2b5e942727cead40775d2395 from qemu
The CPU ID registers ID_AA64PFR0_EL1, ID_PFR1_EL1 and ID_PFR1
have a field for reporting presence of GICv3 system registers.
We need to report this field correctly in order for Xen to
work as a guest inside QEMU emulation. We mustn't incorrectly
claim the sysregs exist when they don't, though, or Linux will
crash.
Unfortunately the way we've designed the GICv3 emulation in QEMU
puts the system registers as part of the GICv3 device, which
may be created after the CPU proper has been realized. This
means that we don't know at the point when we define the ID
registers what the correct value is. Handle this by switching
them to calling a function at runtime to read the value, where
we can fill in the GIC field appropriately.
Backports commit 96a8b92ed8f02d5e86ad380d3299d9f41f99b072 from qemu
For the SG instruction and secure function return we are going
to want to do memory accesses using the MMU index of the CPU
in secure state, even though the CPU is currently in non-secure
state. Write arm_v7m_mmu_idx_for_secstate() to do this job,
and use it in cpu_mmu_index().
Backports commit b81ac0eb6315e602b18439961e0538538e4aed4f from qemu
In cpu_mmu_index() we try to do this:
if (env->v7m.secure) {
mmu_idx += ARMMMUIdx_MSUser;
}
but it will give the wrong answer, because ARMMMUIdx_MSUser
includes the 0x40 ARM_MMU_IDX_M field, and so does the
mmu_idx we're adding to, and we'll end up with 0x8n rather
than 0x4n. This error is then nullified by the call to
arm_to_core_mmu_idx() which masks out the high part, but
we're about to factor out the code that calculates the
ARMMMUIdx values so it can be used without passing it through
arm_to_core_mmu_idx(), so fix this bug first.
Backports commit fe768788d29597ee56fc11ba2279d502c2617457 from qemu
Implement the register interface for the SAU: SAU_CTRL,
SAU_TYPE, SAU_RNR, SAU_RBAR and SAU_RLAR. None of the
actual behaviour is implemented here; registers just
read back as written.
When the CPU definition for Cortex-M33 is eventually
added, its initfn will set cpu->sau_sregion, in the same
way that we currently set cpu->pmsav7_dregion for the
M3 and M4.
Number of SAU regions is typically a configurable
CPU parameter, but this patch doesn't provide a
QEMU CPU property for it. We can easily add one when
we have a board that requires it.
Backports commit 9901c576f6c02d43206e5faaf6e362ab7ea83246 from qemu
Add the new M profile Secure Fault Status Register
and Secure Fault Address Register.
Backports commit bed079da04dd9e0e249b9bc22bca8dce58b67f40 from qemu
In the v7M architecture, there is an invariant that if the CPU is
in Handler mode then the CONTROL.SPSEL bit cannot be nonzero.
This in turn means that the current stack pointer is always
indicated by CONTROL.SPSEL, even though Handler mode always uses
the Main stack pointer.
In v8M, this invariant is removed, and CONTROL.SPSEL may now
be nonzero in Handler mode (though Handler mode still always
uses the Main stack pointer). In preparation for this change,
change how we handle this bit: rename switch_v7m_sp() to
the now more accurate write_v7m_control_spsel(), and make it
check both the handler mode state and the SPSEL bit.
Note that this implicitly changes the point at which we switch
active SP on exception exit from before we pop the exception
frame to after it.
Backports commit de2db7ec894f11931932ca78cd14a8d2b1389d5b from qemu
Now that we have a banked FAULTMASK register and banked exceptions,
we can implement the correct check in cpu_mmu_index() for whether
the MPU_CTRL.HFNMIENA bit's effect should apply. This bit causes
handlers which have requested a negative execution priority to run
with the MPU disabled. In v8M the test has to check this for the
current security state and so takes account of banking.
Backports relevant part of commit 5d4791991d4de12e83d44738417c9e964167b6e8 from qemu
Use a symbolic constant M_REG_NUM_BANKS for the array size for
registers which are banked by M profile security state, rather
than hardcoding lots of 2s.
Backports commit 4a16724f06ead684a5962477a557c26c677c2729 from qemu
Implement the BXNS v8M instruction, which is like BX but will do a
jump-and-switch-to-NonSecure if the branch target address has bit 0
clear.
This is the first piece of code which implements "switch to the
other security state", so the commit also includes the code to
switch the stack pointers around, which is the only complicated
part of switching security state.
BLXNS is more complicated than just "BXNS but set the link register",
so we leave it for a separate commit.
Backports commit fb602cb726b3ebdd01ef3b1732d74baf9fee7ec9 from qemu
Make the CFSR register banked if v8M security extensions are enabled.
Not all the bits in this register are banked: the BFSR
bits [15:8] are shared between S and NS, and we store them
in the NS copy of the register.
Backports commit 334e8dad7a109d15cb20b090131374ae98682a50 from qemu
Make the CCR register banked if v8M security extensions are enabled.
This is slightly more complicated than the other "add banking"
patches because there is one bit in the register which is not
banked. We keep the live data in the NS copy of the register,
and adjust it on register reads and writes. (Since we don't
currently implement the behaviour that the bit controls, there
is nowhere else that needs to care.)
This patch includes the enforcement of the bits which are newly
RES1 in ARMv8M.
Backports commit 9d40cd8a68cfc7606f4548cc9e812bab15c6dc28 from qemu
Make the MPU registers MPU_MAIR0 and MPU_MAIR1 banked if v8M security
extensions are enabled.
We can freely add more items to vmstate_m_security without
breaking migration compatibility, because no CPU currently
has the ARM_FEATURE_M_SECURITY bit enabled and so this
subsection is not yet used by anything.
Backports commit 62c58ee0b24eafb44c06402fe059fbd7972eb409 from qemu
Make the MPU registers MPU_MAIR0 and MPU_MAIR1 banked if v8M security
extensions are enabled.
Backports commit 4125e6feb71c810ca38f0d8e66e748b472a9cc54 from qemu
Make the FAULTMASK register banked if v8M security extensions are enabled.
Note that we do not yet implement the functionality of the new
AIRCR.PRIS bit (which allows the effect of the NS copy of FAULTMASK to
be restricted).
This patch includes the code to determine for v8M which copy
of FAULTMASK should be updated on exception exit; further
changes will be required to the exception exit code in general
to support v8M, so this is just a small piece of that.
The v8M ARM ARM introduces a notation where individual paragraphs
are labelled with R (for rule) or I (for information) followed
by a random group of subscript letters. In comments where we want
to refer to a particular part of the manual we use this convention,
which should be more stable across document revisions than using
section or page numbers.
Backports commit 42a6686b2f6199d086a58edd7731faeb2dbe7c14 from qemu
Make the PRIMASK register banked if v8M security extensions are enabled.
Note that we do not yet implement the functionality of the new
AIRCR.PRIS bit (which allows the effect of the NS copy of PRIMASK to
be restricted).
Backports commit 6d8048341995b31a77dc2e0dcaaf4e3df0e3121a from qemu
Make the BASEPRI register banked if v8M security extensions are enabled.
Note that we do not yet implement the functionality of the new
AIRCR.PRIS bit (which allows the effect of the NS copy of BASEPRI to
be restricted).
Backports commit acf949411ffb675edbfb707e235800b02e6a36f8 from qemu
Now that MPU lookups can return different results for v8M
when the CPU is in secure vs non-secure state, we need to
have separate MMU indexes; add the secure counterparts
to the existing three M profile MMU indexes.
Backports commit 66787c7868d05d29974e09201611b718c976f955 from qemu
As part of ARMv8M, we need to add support for the PMSAv8 MPU
architecture.
PMSAv8 differs from PMSAv7 both in register/data layout (for instance
using base and limit registers rather than base and size) and also in
behaviour (for example it does not have subregions); rather than
trying to wedge it into the existing PMSAv7 code and data structures,
we define separate ones.
This commit adds the data structures which hold the state for a
PMSAv8 MPU and the register interface to it. The implementation of
the MPU behaviour will be added in a subsequent commit.
Backports commit 0e1a46bbd2d6c39614b87f4e88ea305acce8a35f from qemu
Add a utility function for testing whether the CPU is in Handler
mode; this is just a check whether v7m.exception is non-zero, but
we do it in several places and it makes the code a bit easier
to read to not have to mentally figure out what the test is testing.
Backports commit 15b3f556bab4f961bf92141eb8521c8da3df5eb2 from qemu
We currently store the M profile CPU register state PRIMASK and
FAULTMASK in the daif field of the CPU state in its I and F
bits. This is a legacy from the original implementation, which
tried to share the cpu_exec_interrupt code between A profile
and M profile. We've since separated out the two cases because
they are significantly different, so now there is no common
code between M and A profile which looks at env->daif: all the
uses are either in A-only or M-only code paths. Sharing the state
fields now is just confusing, and will make things awkward
when we implement v8M, where the PRIMASK and FAULTMASK
registers are banked between security states.
Switch M profile over to using v7m.faultmask and v7m.primask
fields for these registers.
Backports commit e6ae5981ea4b0f6feb223009a5108582e7644f8f from qemu
The M profile XPSR is almost the same format as the A profile CPSR,
but not quite. Define some XPSR_* macros and use them where we
definitely dealing with an XPSR rather than reusing the CPSR ones.
Backports commit 987ab45e108953c1c98126c338c2119c243c372b from qemu
Remove the comment that claims that some MPU_CTRL bits are stored
in sctlr_el[1]. This has never been true since MPU_CTRL was added
in commit 29c483a50607 -- the comment is a leftover from
Michael Davidsaver's original implementation, which I modified
not to use sctlr_el[1]; I forgot to delete the comment then.
Backports commit 59e4972c3fc63d981e8b613ebb3bb01a05848075 from qemu
Almost all of the PMSAv7 state is in the pmsav7 substruct of
the ARM CPU state structure. The exception is the region
number register, which is in cp15.c6_rgnr. This exception
is a bit odd for M profile, which otherwise generally does
not store state in the cp15 substruct.
Rename cp15.c6_rgnr to pmsav7.rnr accordingly.
Backports commit 8531eb4f614a60e6582d4832b15eee09f7d27874 from qemu
Implement the exception return consistency checks
described in the v7M pseudocode ExceptionReturn().
Inspired by a patch from Michael Davidsaver's series, but
this is a reimplementation from scratch based on the
ARM ARM pseudocode.
Backports commit aa488fe3bb5460c6675800ccd80f6dccbbd70159 from qemu
The M profile condition for when we can take a pending exception or
interrupt is not the same as that for A/R profile. The code
originally copied from the A/R profile version of the
cpu_exec_interrupt function only worked by chance for the
very simple case of exceptions being masked by PRIMASK.
Replace it with a call to a function in the NVIC code that
correctly compares the priority of the pending exception
against the current execution priority of the CPU.
Backports commit 7ecdaa4a9635f1ded0dfa9218c25273b6d4dcd44 from qemu
Having armv7m_nvic_acknowledge_irq() return the new value of
env->v7m.exception and its one caller assign the return value
back to env->v7m.exception is pointless. Just make the return
type void instead.
Backports commit a5d8235545e98c1ce02560d5f4f57552d937efe9 from qemu
Implement HFNMIENA support for the M profile MPU. This bit controls
whether the MPU is treated as enabled when executing at execution
priorities of less than zero (in NMI, HardFault or with the FAULTMASK
bit set).
Doing this requires us to use a different MMU index for "running
at execution priority < 0", because we will have different
access permissions for that case versus the normal case.
Backports commit 3bef7012560a7f0ea27b265105de5090ba117514 from qemu
The M series MPU is almost the same as the already implemented R
profile MPU (v7 PMSA). So all we need to implement here is the MPU
register interface in the system register space.
This implementation has the same restriction as the R profile MPU
that it doesn't permit regions to be sized down smaller than 1K.
We also do not yet implement support for MPU_CTRL.HFNMIENA; this
bit should if zero disable use of the MPU when running HardFault,
NMI or with FAULTMASK set to 1 (ie at an execution priority of
less than zero) -- if the MPU is enabled we don't treat these
cases any differently.
Backports commit 29c483a506070e8f554c77d22686f405e30b9114 from qemu
ARM CPUs come in two flavours:
* proper MMU ("VMSA")
* only an MPU ("PMSA")
For PMSA, the MPU may be implemented, or not (in which case there
is default "always acts the same" behaviour, but it isn't guest
programmable).
QEMU is a bit confused about how we indicate this: we have an
ARM_FEATURE_MPU, but it's not clear whether this indicates
"PMSA, not VMSA" or "PMSA and MPU present" , and sometimes we
use it for one purpose and sometimes the other.
Currently trying to implement a PMSA-without-MPU core won't
work correctly because we turn off the ARM_FEATURE_MPU bit
and then a lot of things which should still exist get
turned off too.
As the first step in cleaning this up, rename the feature
bit to ARM_FEATURE_PMSA, which indicates a PMSA CPU (with
or without MPU).
Backports commit 452a095526a0537f16c271516a2200877a272ea8 from qemu
Make M profile use completely separate ARMMMUIdx values from
those that A profile CPUs use. This is a prelude to adding
support for the MPU and for v8M, which together will require
6 MMU indexes which don't map cleanly onto the A profile
uses:
non secure User
non secure Privileged
non secure Privileged, execution priority < 0
secure User
secure Privileged
secure Privileged, execution priority < 0
Backports commit e7b921c2d9efc249f99b9feb0e7dca82c96aa5c4 from qemu
The M profile CPU's MPU has an awkward corner case which we
would like to implement with a different MMU index.
We can avoid having to bump the number of MMU modes ARM
uses, because some of our existing MMU indexes are only
used by non-M-profile CPUs, so we can borrow one.
To avoid that getting too confusing, clean up the code
to try to keep the two meanings of the index separate.
Instead of ARMMMUIdx enum values being identical to core QEMU
MMU index values, they are now the core index values with some
high bits set. Any particular CPU always uses the same high
bits (so eventually A profile cores and M profile cores will
use different bits). New functions arm_to_core_mmu_idx()
and core_to_arm_mmu_idx() convert between the two.
In general core index values are stored in 'int' types, and
ARM values are stored in ARMMMUIdx types.
Backports commit 8bd5c82030b2cb09d3eef6b444f1620911cc9fc5 from qemu
For M profile exception-return handling we'd like to generate different
code for some instructions depending on whether we are in Handler
mode or Thread mode. This isn't the same as "are we privileged
or user", so we need an extra bit in the TB flags to distinguish.
Backports commit 064c379c99b835bdcc478d21a3849507ea07d53a from qemu
The excnames[] array is defined in internals.h because we used
to use it from two different source files for handling logging
of AArch32 and AArch64 exception entry. Refactoring means that
it's now used only in arm_log_exception() in helper.c, so move
the array into that function.
Backports commit 2c4a7cc5afb1bfc1728a39abd951ddd7714c476e from qemu
Recent changes have added new EXCP_ values to ARM but forgot
to update the excnames[] array which is used to provide
human-readable strings when printing information about the
exception for debug logging. Add the missing entries, and
add a comment to the list of #defines to help avoid the mistake
being repeated in future.
Backports commit 32b81e620ea562d56ab2733421b5da1082b237a2 from qemu
For v7M attempts to access a nonexistent coprocessor are reported
differently from plain undefined instructions (as UsageFaults of type
NOCP rather than type UNDEFINSTR). Split them out into a new
EXCP_NOCP so we can report the FSR value correctly.
Backports commit 7517748e3f71a3099e57915fba95c4c308e6d842 from qemu
Add the structure fields, VMState fields, reset code and macros for
the v7M system control registers CCR, CFSR, HFSR, DFSR, MMFAR and
BFAR.
Backports commit 2c4da50d9477fb830d778bb5d6a11215aa359b44 from qemu
The v7m CONTROL register bit 1 is SPSEL, which indicates
the stack being used. We were storing this information
not in v7m.control but in the separate v7m.other_sp
structure field. Unfortunately, the code handling reads
of the CONTROL register didn't take account of this, and
so if SPSEL was updated by an exception entry or exit then
a subsequent guest read of CONTROL would get the wrong value.
Using a separate structure field doesn't really gain us
anything in efficiency, so drop this unnecessary complexity
in favour of simply storing all the bits in v7m.control.
This is a migration compatibility break for M profile
CPUs only.
Backports commit abc24d86cc0364f402e438fae3acb14289b40734 from qemu
The power state spec section 5.1.5 AFFINITY_INFO defines the
affinity info return values as
0 ON
1 OFF
2 ON_PENDING
I grepped QEMU for power_state to ensure that no assumptions
of OFF=0 were being made.
Backports commit d5affb0d8677e1a8a8fe03fa25005b669e7cdc02 from qemu
This enables the multi-threaded system emulation by default for ARMv7
and ARMv8 guests using the x86_64 TCG backend. This is because on the
guest side:
- The ARM translate.c/translate-64.c have been converted to
- use MTTCG safe atomic primitives
- emit the appropriate barrier ops
- The ARM machine has been updated to
- hold the BQL when modifying shared cross-vCPU state
- defer powerctl changes to async safe work
All the host backends support the barrier and atomic primitives but
need to provide same-or-better support for normal load/store
operations.
Backports commit ca759f9e387db87e1719911f019bc60c74be9ed8 from qemu
In order to support Linux perf, which uses PMXEVTYPER register,
this patch adds read/write access support for PMXEVTYPER. The access
is CONSTRAINED UNPREDICTABLE when PMSELR is not 0x1f. Additionally
this patch adds support for PMXEVTYPER_EL0.
Backports commit fdb8665672ded05f650d18f8b62d5c8524b4385b from qemu
This patch adds support for AArch64 register PMSELR_EL0. The existing
PMSELR definition is revised accordingly.
Backports commit 6b0407805d46bbeba70f4be426285d0a0e669750 from qemu
Add a new "cfgend" property which selects whether the CPU resets into
big-endian mode or not. This setting affects whether we reset with
SCTLR_B (ARMv6 and earlier) or SCTLR_EE (ARMv7 and later) set.
Backports commit 3a062d5730266b2386eeda68b1a1c6e96451db31 from qemu
We only use the IS_M() macro in two places, and it's a bit of a
namespace grab to put in cpu.h. Drop it in favour of just explicitly
calling arm_feature() in the places where it was used.
Backports commit 531c60a97ab51618b4b9ccef1c5fe00607079706 from qemu
Enable the ARM_FEATURE_EL2 bit on Cortex-A52 and
Cortex-A57, since this is all now sufficiently implemented
to work with the GICv3. We provide the usual CPU property
to disable it for backwards compatibility with the older
virt boards.
In this commit, we disable the EL2 feature on the
virt and ZynpMP boards, so there is no overall effect.
Another commit will expose a board-level property to
allow the user to enable EL2.
Backports commit c25bd18a04c8bd0f19556d719864b7b08528222d from qemu
We've currently got 18 architectures in QEMU, and thus 18 target-xxx
folders in the root folder of the QEMU source tree. More architectures
(e.g. RISC-V, AVR) are likely to be included soon, too, so the main
folder of the QEMU sources slowly gets quite overcrowded with the
target-xxx folders.
To disburden the main folder a little bit, let's move the target-xxx
folders into a dedicated target/ folder, so that target-xxx/ simply
becomes target/xxx/ instead.
Backports commit fcf5ef2ab52c621a4617ebbef36bf43b4003f4c0 from qemu
