The x87 f2xm1 emulation is currently based around conversion to
double. This is inherently unsuitable for a good emulation of any
floatx80 operation, even before considering that it is a particularly
naive implementation using double (computing with pow and then
subtracting 1 rather than attempting a better emulation using expm1).
Reimplement using the soft-float operations, including additions and
multiplications with higher precision where appropriate to limit
accumulation of errors. I considered reusing some of the m68k code
for transcendental operations, but the instructions don't generally
correspond exactly to x87 operations (for example, m68k has 2^x and
e^x - 1, but not 2^x - 1); to avoid possible accumulation of errors
from applying multiple such operations each rounding to floatx80
precision, I wrote a direct implementation of 2^x - 1 instead. It
would be possible in principle to make the implementation more
efficient by doing the intermediate operations directly with
significands, signs and exponents and not packing / unpacking floatx80
format for each operation, but that would make it significantly more
complicated and it's not clear that's worthwhile; the m68k emulation
doesn't try to do that.
A test is included with many randomly generated inputs. The
assumption of the test is that the result in round-to-nearest mode
should always be one of the two closest floating-point numbers to the
mathematical value of 2^x - 1; the implementation aims to do somewhat
better than that (about 70 correct bits before rounding). I haven't
investigated how accurate hardware is.
Backports commit eca30647fc078f4d9ed1b455bd67960f99dbeb7a from qemu
The last real change to this file is from 2012, so it is very likely
that this file is completely out-of-date and ignored today. Let's
simply remove it to avoid confusion if someone finds it by accident.
Backports commit 3575b0aea983ad57804c9af739ed8ff7bc168393 from qemu
This corrects a bug introduced in my previous fix for SSE4.2 pcmpestri
/ pcmpestrm / pcmpistri / pcmpistrm substring search, commit
ae35eea7e4a9f21dd147406dfbcd0c4c6aaf2a60.
That commit fixed a bug that showed up in four GCC tests with one libc
implementation. The tests in question generate random inputs to the
intrinsics and compare results to a C implementation, but they only
test 1024 possible random inputs, and when the tests use the cases of
those instructions that work with word rather than byte inputs, it's
easy to have problematic cases that show up much less frequently than
that. Thus, testing with a different libc implementation, and so a
different random number generator, showed up a problem with the
previous patch.
When investigating the previous test failures, I found the description
of these instructions in the Intel manuals (starting from computing a
16x16 or 8x8 set of comparison results) confusing and hard to match up
with the more optimized implementation in QEMU, and referred to AMD
manuals which described the instructions in a different way. Those
AMD descriptions are very explicit that the whole of the string being
searched for must be found in the other operand, not running off the
end of that operand; they say "If the prototype and the SUT are equal
in length, the two strings must be identical for the comparison to be
TRUE.". However, that statement is incorrect.
In my previous commit message, I noted:
The operation in this case is a search for a string (argument d to
the helper) in another string (argument s to the helper); if a copy
of d at a particular position would run off the end of s, the
resulting output bit should be 0 whether or not the strings match in
the region where they overlap, but the QEMU implementation was
wrongly comparing only up to the point where s ends and counting it
as a match if an initial segment of d matched a terminal segment of
s. Here, "run off the end of s" means that some byte of d would
overlap some byte outside of s; thus, if d has zero length, it is
considered to match everywhere, including after the end of s.
The description "some byte of d would overlap some byte outside of s"
is accurate only when understood to refer to overlapping some byte
*within the 16-byte operand* but at or after the zero terminator; it
is valid to run over the end of s if the end of s is the end of the
16-byte operand. So the fix in the previous patch for the case of d
being empty was correct, but the other part of that patch was not
correct (as it never allowed partial matches even at the end of the
16-byte operand). Nor was the code before the previous patch correct
for the case of d nonempty, as it would always have allowed partial
matches at the end of s.
Fix with a partial revert of my previous change, combined with
inserting a check for the special case of s having maximum length to
determine where it is necessary to check for matches.
In the added test, test 1 is for the case of empty strings, which
failed before my 2017 patch, test 2 is for the bug introduced by my
2017 patch and test 3 deals with the case where a match of an initial
segment at the end of the string is not valid when the string ends
before the end of the 16-byte operand (that is, the case that would be
broken by a simple revert of the non-empty-string part of my 2017
patch).
Backports commit bc921b2711c4e2e8ab99a3045f6c0f134a93b535 from qemu
Most x87 instruction implementations fail to raise the expected IEEE
floating-point exceptions because they do nothing to convert the
exception state from the softfloat machinery into the exception flags
in the x87 status word. There is special-case handling of division to
raise the divide-by-zero exception, but that handling is itself buggy:
it raises the exception in inappropriate cases (inf / 0 and nan / 0,
which should not raise any exceptions, and 0 / 0, which should raise
"invalid" instead).
Fix this by converting the floating-point exceptions raised during an
operation by the softfloat machinery into exceptions in the x87 status
word (passing through the existing fpu_set_exception function for
handling related to trapping exceptions). There are special cases
where some functions convert to integer internally but exceptions from
that conversion are not always correct exceptions for the instruction
to raise.
There might be scope for some simplification if the softfloat
exception state either could always be assumed to be in sync with the
state in the status word, or could always be ignored at the start of
each instruction and just set to 0 then; I haven't looked into that in
detail, and it might run into interactions with the various ways the
emulation does not yet handle trapping exceptions properly. I think
the approach taken here, of saving the softfloat state, setting
exceptions there to 0 and then merging the old exceptions back in
after carrying out the operation, is conservatively safe
Backports commit 975af797f1e04e4d1b1a12f1731141d3770fdbce from qemu
The fist / fistt family of instructions should all store the most
negative integer in the destination format when the rounded /
truncated integer result is out of range or the input is an invalid
encoding, infinity or NaN. The fisttpl and fisttpll implementations
(32-bit and 64-bit results, truncate towards zero) failed to do this,
producing the most positive integer in some cases instead. Fix this
by copying the code used to handle this issue for fistpl and fistpll,
adjusted to use the _round_to_zero functions for the actual
conversion (but without any other changes to that code).
Backports commit c8af85b10c818709755f5dc8061c69920611fd4c from qemu
The fbstp implementation fails to check for out-of-range and invalid
values, instead just taking the result of conversion to int64_t and
storing its sign and low 18 decimal digits. Fix this by checking for
an out-of-range result (invalid conversions always result in INT64_MAX
or INT64_MIN from the softfloat code, which are large enough to be
considered as out-of-range by this code) and storing the packed BCD
indefinite encoding in that case.
Backports commit 374ff4d0a3c2cce2bc6e4ba8a77eaba55c165252 from qemu
The fbstp implementation stores +0 when the rounded result should be
-0 because it compares an integer value with 0 to determine the sign.
Fix this by checking the sign bit of the operand instead.
Backports commit 18c53e1e73197a24f9f4b66b1276eb9868db5bf0 from qemu
The fxam implementation does not check for invalid encodings, instead
treating them like NaN or normal numbers depending on the exponent.
Fix it to check that the high bit of the significand is set before
treating an encoding as NaN or normal, thus resulting in correct
handling (all of C0, C2 and C3 cleared) for invalid encodings.
Backports commit 34b9cc076ff423023a779a04a9f7cd7c17372cbf from qemu
The implementations of the fldl2t, fldl2e, fldpi, fldlg2 and fldln2
instructions load fixed constants independent of the rounding mode.
Fix them to load a value correctly rounded for the current rounding
mode (but always rounded to 64-bit precision independent of the
precision control, and without setting "inexact") as specified.
Backports commit 80b4008c805ebcfd4c0d302ac31c1689e34571e0 from qemu
The fscale implementation uses floatx80_scalbn for the final scaling
operation. floatx80_scalbn ends up rounding the result using the
dynamic rounding precision configured for the FPU. But only a limited
set of x87 floating-point instructions are supposed to respect the
dynamic rounding precision, and fscale is not in that set. Fix the
implementation to save and restore the rounding precision around the
call to floatx80_scalbn.
Backports commit c535d68755576bfa33be7aef7bd294a601f776e0 from qemu
The fscale implementation passes infinite exponents through to generic
code that rounds the exponent to a 32-bit integer before using
floatx80_scalbn. In round-to-nearest mode, and ignoring exceptions,
this works in many cases. But it fails to handle the special cases of
scaling 0 by a +Inf exponent or an infinity by a -Inf exponent, which
should produce a NaN, and because it produces an inexact result for
finite nonzero numbers being scaled, the result is sometimes incorrect
in other rounding modes. Add appropriate handling of infinite
exponents to produce a NaN or an appropriately signed exact zero or
infinity as a result
Backports commit c1c5fb8f9067c830e36830c2b82c0ec146c03d7b from qemu
The fscale implementation does not check for invalid encodings in the
exponent operand, thus treating them like INT_MIN (the value returned
for invalid encodings by floatx80_to_int32_round_to_zero). Fix it to
treat them similarly to signaling NaN exponents, thus generating a
quiet NaN result.
Backports commit b40eec96b26028b68c3594fbf34b6d6f029df26a from qemu
The implementation of the fscale instruction returns a NaN exponent
unchanged. Fix it to return a quiet NaN when the provided exponent is
a signaling NaN.
Backports commit 0d48b436327955c69e2eb53f88aba9aa1e0dbaa0 from qemu
The implementation of the fxtract instruction treats all nonzero
operands as normal numbers, so yielding incorrect results for invalid
formats, infinities, NaNs and subnormal and pseudo-denormal operands.
Implement appropriate handling of all those cases.
Backports commit c415f2c58296d86e9abb7e4a133111acf7031da3 from qemu
Detected by asm test suite failures in dav1d
(https://code.videolan.org/videolan/dav1d). Can be reproduced by
`qemu-x86_64 -cpu core2duo ./tests/checkasm --test=mc_8bpc 1659890620`.
Backports commit 2dfbea1a872727fb747ca6adf2390e09956cdc6e from qemu
Give the previously unnamed enum a typedef name. Use it in the
prototypes of compare functions. Use it to hold the results
of the compare functions.
Backports commit 71bfd65c5fcd72f8af2735905415c7ce4220f6dc from qemu
Fixes the following coccinelle warnings:
$ spatch --sp-file --verbose-parsing ... \
scripts/coccinelle/remove_local_err.cocci
...
SUSPICIOUS: a \ character appears outside of a #define at ./target/ppc/translate_init.inc.c:5213
SUSPICIOUS: a \ character appears outside of a #define at ./target/ppc/translate_init.inc.c:5261
SUSPICIOUS: a \ character appears outside of a #define at ./target/microblaze/cpu.c:166
SUSPICIOUS: a \ character appears outside of a #define at ./target/microblaze/cpu.c:167
SUSPICIOUS: a \ character appears outside of a #define at ./target/microblaze/cpu.c:169
SUSPICIOUS: a \ character appears outside of a #define at ./target/microblaze/cpu.c:170
SUSPICIOUS: a \ character appears outside of a #define at ./target/microblaze/cpu.c:171
SUSPICIOUS: a \ character appears outside of a #define at ./target/microblaze/cpu.c:172
SUSPICIOUS: a \ character appears outside of a #define at ./target/microblaze/cpu.c:173
SUSPICIOUS: a \ character appears outside of a #define at ./target/i386/cpu.c:5787
SUSPICIOUS: a \ character appears outside of a #define at ./target/i386/cpu.c:5789
SUSPICIOUS: a \ character appears outside of a #define at ./target/i386/cpu.c:5800
SUSPICIOUS: a \ character appears outside of a #define at ./target/i386/cpu.c:5801
SUSPICIOUS: a \ character appears outside of a #define at ./target/i386/cpu.c:5802
SUSPICIOUS: a \ character appears outside of a #define at ./target/i386/cpu.c:5804
SUSPICIOUS: a \ character appears outside of a #define at ./target/i386/cpu.c:5805
SUSPICIOUS: a \ character appears outside of a #define at ./target/i386/cpu.c:5806
SUSPICIOUS: a \ character appears outside of a #define at ./target/i386/cpu.c:6329
SUSPICIOUS: a \ character appears outside of a #define at ./hw/sd/sdhci.c:1133
SUSPICIOUS: a \ character appears outside of a #define at ./hw/scsi/scsi-disk.c:3081
SUSPICIOUS: a \ character appears outside of a #define at ./hw/net/virtio-net.c:1529
SUSPICIOUS: a \ character appears outside of a #define at ./hw/riscv/sifive_u.c:468
SUSPICIOUS: a \ character appears outside of a #define at ./dump/dump.c:1895
SUSPICIOUS: a \ character appears outside of a #define at ./block/vhdx.c:2209
SUSPICIOUS: a \ character appears outside of a #define at ./block/vhdx.c:2215
SUSPICIOUS: a \ character appears outside of a #define at ./block/vhdx.c:2221
SUSPICIOUS: a \ character appears outside of a #define at ./block/vhdx.c:2222
SUSPICIOUS: a \ character appears outside of a #define at ./block/replication.c:172
SUSPICIOUS: a \ character appears outside of a #define at ./block/replication.c:173
Backports commit 78ee6bd04821847036a805cb4bdd46464e1d3098 from qemu
We are not short of numbers for EXCP_*. There is no need to confuse things
by having EXCP_VMEXIT and EXCP_SYSCALL overlap, even though the former is
only used for system mode and the latter is only used for user mode.
Backports commit 628460891dd46c25e33eec01757ac655679ea198 from qemu
Adds the support for 2nd Gen AMD EPYC Processors. The model display
name will be EPYC-Rome.
Adds the following new feature bits on top of the feature bits from the
first generation EPYC models.
perfctr-core : core performance counter extensions support. Enables the VM to
use extended performance counter support. It enables six
programmable counters instead of four counters.
clzero : instruction zeroes out the 64 byte cache line specified in RAX.
xsaveerptr : XSAVE, XSAVE, FXSAVEOPT, XSAVEC, XSAVES always save error
pointers and FXRSTOR, XRSTOR, XRSTORS always restore error
pointers.
wbnoinvd : Write back and do not invalidate cache
ibpb : Indirect Branch Prediction Barrier
amd-stibp : Single Thread Indirect Branch Predictor
clwb : Cache Line Write Back and Retain
xsaves : XSAVES, XRSTORS and IA32_XSS support
rdpid : Read Processor ID instruction support
umip : User-Mode Instruction Prevention support
The Reference documents are available at
https://developer.amd.com/wp-content/resources/55803_0.54-PUB.pdfhttps://www.amd.com/system/files/TechDocs/24594.pdf
Depends on following kernel commits:
40bc47b08b6e ("kvm: x86: Enumerate support for CLZERO instruction")
504ce1954fba ("KVM: x86: Expose XSAVEERPTR to the guest")
6d61e3c32248 ("kvm: x86: Expose RDPID in KVM_GET_SUPPORTED_CPUID")
52297436199d ("kvm: svm: Update svm_xsaves_supported")
Backports commit 143c30d4d346831a09e59e9af45afdca0331e819 from qem
Adds the following missing CPUID bits:
perfctr-core : core performance counter extensions support. Enables the VM
to use extended performance counter support. It enables six
programmable counters instead of 4 counters.
clzero : instruction zeroes out the 64 byte cache line specified in RAX.
xsaveerptr : XSAVE, XSAVE, FXSAVEOPT, XSAVEC, XSAVES always save error
pointers and FXRSTOR, XRSTOR, XRSTORS always restore error
pointers.
ibpb : Indirect Branch Prediction Barrie.
xsaves : XSAVES, XRSTORS and IA32_XSS supported.
Depends on following kernel commits:
40bc47b08b6e ("kvm: x86: Enumerate support for CLZERO instruction")
504ce1954fba ("KVM: x86: Expose XSAVEERPTR to the guest")
52297436199d ("kvm: svm: Update svm_xsaves_supported")
These new features will be added in EPYC-v3. The -cpu help output after the change.
x86 EPYC-v1 AMD EPYC Processor
x86 EPYC-v2 AMD EPYC Processor (with IBPB)
x86 EPYC-v3 AMD EPYC Processor
Backports commit a16e8dbc043720abcb37fc7dca313e720b4e0f0c from qemu
Because MPX is being removed from the linux kernel, remove MPX feature
from Denverton.
Backports commit ab0c942c868210e78ff88aef83efb4b4018068e1 from qemu
The fxam instruction returns the wrong result after fdecstp or after
an underflow. Check fptags to handle this.
Backports commit 93c3593ad04f2610fd0a176dfa89a7e40b6afe1f from qemu
This fixes a confusion in the help output. (Although, if you squint
long enough at the '-cpu help' output, you _do_ notice that
"Skylake-Client-noTSX-IBRS" is an alias of "Skylake-Client-v3";
similarly for Skylake-Server-v3.)
Without this patch:
$ qemu-system-x86 -cpu help
...
x86 Skylake-Client-v1 Intel Core Processor (Skylake)
x86 Skylake-Client-v2 Intel Core Processor (Skylake, IBRS)
x86 Skylake-Client-v3 Intel Core Processor (Skylake, IBRS)
...
x86 Skylake-Server-v1 Intel Xeon Processor (Skylake)
x86 Skylake-Server-v2 Intel Xeon Processor (Skylake, IBRS)
x86 Skylake-Server-v3 Intel Xeon Processor (Skylake, IBRS)
...
With this patch:
$ ./qemu-system-x86 -cpu help
...
x86 Skylake-Client-v1 Intel Core Processor (Skylake)
x86 Skylake-Client-v2 Intel Core Processor (Skylake, IBRS)
x86 Skylake-Client-v3 Intel Core Processor (Skylake, IBRS, no TSX)
...
x86 Skylake-Server-v1 Intel Xeon Processor (Skylake)
x86 Skylake-Server-v2 Intel Xeon Processor (Skylake, IBRS)
x86 Skylake-Server-v3 Intel Xeon Processor (Skylake, IBRS, no TSX)
Backports commit 673b0add9ea7f432f34c1c99eaa7c567012fc838 from qemu
Fixes:
target/arm/translate-a64.c: In function 'disas_crypto_three_reg_sha512':
target/arm/translate-a64.c:13625:9: error: 'genfn' may be used uninitialized in this function [-Werror=maybe-uninitialized]
genfn(tcg_rd_ptr, tcg_rn_ptr, tcg_rm_ptr);
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
qemu/target/arm/translate-a64.c:13609:8: error: 'feature' may be used uninitialized in this function [-Werror=maybe-uninitialized]
if (!feature) {
Backports commit c7a5e7910517e2711215a9e869a733ffde696091 from qemu
It lacks VMX features and two security feature bits (disclosed recently) in
MSR_IA32_ARCH_CAPABILITIES in current Cooperlake CPU model, so add them.
Fixes: 22a866b6166d ("i386: Add new CPU model Cooperlake")
Backports commit 2dea9d9ca4ea7e9afe83d0b4153b21a16987e866 from qemu
The bit 6, 7 and 8 of MSR_IA32_ARCH_CAPABILITIES are recently disclosed
for some security issues. Add the definitions for them to be used by named
CPU models.
Backports commit 6c997b4adb300788d61d72e2b8bc67c03a584956 from qemu
Cooper Lake is intel's successor to Cascade Lake, the new
CPU model inherits features from Cascadelake-Server, while
add one platform associated new feature: AVX512_BF16. Meanwhile,
add STIBP for speculative execution.
Backports commit 22a866b6166db5caa4abaa6e656c2a431fa60726 from qemu
stibp feature is already added through the following commit.
0e89165829
Add a macro for it to allow CPU models to report it when host supports.
Backports commit 5af514d0cb314f43bc53f2aefb437f6451d64d0c from qemu
Define MSR_ARCH_CAP_MDS_NO in the IA32_ARCH_CAPABILITIES MSR to allow
CPU models to report the feature when host supports it.
Backports commit 77b168d221191156c47fcd8d1c47329dfdb9439e from qemu
Preparation for collapsing the two byte swaps, adjust_endianness and
handle_bswap, along the I/O path.
Target dependant attributes are conditionalized upon NEED_CPU_H.
Backports commit 14776ab5a12972ea439c7fb2203a4c15a09094b4 from qemu
Intel CooperLake cpu adds AVX512_BF16 instruction, defining as
CPUID.(EAX=7,ECX=1):EAX[bit 05].
The patch adds a property for setting the subleaf of CPUID leaf 7 in
case that people would like to specify it.
The release spec link as follows,
https://software.intel.com/sites/default/files/managed/c5/15/\
architecture-instruction-set-extensions-programming-reference.pdf
Backports commit 80db491da4ce8b199e0e8d1e23943b20aab82f69 from qemu
The x86 architecture requires that all conversions from floating
point to integer which raise the 'invalid' exception (infinities of
both signs, NaN, and all values which don't fit in the destination
integer) return what the x86 spec calls the "indefinite integer
value", which is 0x8000_0000 for 32-bits or 0x8000_0000_0000_0000 for
64-bits. The softfloat functions return the more usual behaviour of
positive overflows returning the maximum value that fits in the
destination integer format and negative overflows returning the
minimum value that fits.
Wrap the softfloat functions in x86-specific versions which
detect the 'invalid' condition and return the indefinite integer.
Note that we don't use these wrappers for the 3DNow! pf2id and pf2iw
instructions, which do return the minimum value that fits in
an int32 if the input float is a large negative number.
Fixes: https://bugs.launchpad.net/qemu/+bug/1815423
Backports commit 1e8a98b53867f61da9ca09f411288e2085d323c4 from qemu
Changing the name to Snowridge from SnowRidge-Server.
There is no client model of Snowridge, so "-Server" is unnecessary.
Removing CPUID_EXT_VMX from Snowridge cpu feature list.
Backports commit ff656fcd338a70c4d9783a800733c4ab3806e5b0 from qemu
pconfig feature was added in 5131dc433df and removed in 712f807e196.
This patch mark this feature as known to QEMU and removed by
intentinally. This follows the convention of 9ccb9784b57 and f1a23522b03
dealing with 'osxsave' and 'ospke'.
Backports commit 2924ab02c28ce8d32da144a6ae8bfc5a8d7e072b from qemu
Add new version of Cascadelake-Server CPU model, setting
stepping=5 and enabling the IA32_ARCH_CAPABILITIES MSR
with some flags.
The new feature will introduce a new host software requirement,
breaking our CPU model runnability promises. This means we can't
enable the new CPU model version by default in QEMU 4.1, because
management software isn't ready yet to resolve CPU model aliases.
This is why "pc-*-4.1" will keep returning Cascadelake-Server-v1
if "-cpu Cascadelake-Server" is specified.
Includes a test case to ensure the right combinations of
machine-type + CPU model + command-line feature flags will work
as expected.
Backports commit fd63c6d1a5f77d689ee06f6561677c012a988223 from qemu
The old CPU models will be just aliases for specific versions of
the original CPU models.
Backports commit 53db89d93bebe70a3e7f4c45933deffcf3e7cb62 from qemu
Add versions of CPU models that are equivalent to their -IBRS,
-noTSX and -IBRS variants.
The separate variants will eventually be removed and become
aliases for these CPU versions.
Backports commit d86a708815c3bec0b934760e6bdab7eb647087b8 from qemu
Add support for registration of multiple versions of CPU models.
The existing CPU models will be registered with a "-v1" suffix.
The -noTSX, -IBRS, and -IBPB CPU model variants will become
versions of the original models in a separate patch, so
make sure we register no versions for them.
Backports commit dcafd1ef0af227ef87f7a6dec8fc66d7d2e2442d from qemu
The CPUID.1F as Intel V2 Extended Topology Enumeration Leaf would be
exposed if guests want to emulate multiple software-visible die within
each package. Per Intel's SDM, the 0x1f is a superset of 0xb, thus they
can be generated by almost same code as 0xb except die_offset setting.
If the number of dies per package is greater than 1, the cpuid_min_level
would be adjusted to 0x1f regardless of whether the host supports CPUID.1F.
Likewise, the CPUID.1F wouldn't be exposed if env->nr_dies < 2.
Backports commit a94e1428991f741e2c6636e7c8df7f8d1905d983 from qemu
In new sockets/dies/cores/threads model, the apicid of logical cpu could
imply die level info of guest cpu topology thus x86_apicid_from_cpu_idx()
need to be refactored with #dies value, so does apicid_*_offset().
To keep semantic compatibility, the legacy pkg_offset which helps to
generate CPUIDs such as 0x3 for L3 cache should be mapping to die_offset.
Backports commit d65af288a84d8bf8c27e55d45545f52f016c08a7 from qemu
The field die_id (default as 0) and has_die_id are introduced to X86CPU.
Following the legacy smp check rules, the die_id validity is added to
the same contexts as leagcy smp variables such as hmp_hotpluggable_cpus(),
machine_set_cpu_numa_node(), cpu_slot_to_string() and pc_cpu_pre_plug().
Backports relevant bits from 176d2cda0dee9f4f78f604ad72d6a111e8e38f3b
from qemu
The die-level as the first PC-specific cpu topology is added to the leagcy
cpu topology model, which has one die per package implicitly and only the
numbers of sockets/cores/threads are configurable.
In the new model with die-level support, the total number of logical
processors (including offline) on board will be calculated as:
\#cpus = #sockets * #dies * #cores * #threads
and considering compatibility, the default value for #dies would be
initialized to one in x86_cpu_initfn() and pc_machine_initfn().
Backports commit c26ae610811e8d52f4fc73e3ae0a8bc4a24d6763 from qemu
