QEMU TCG Plugins¶

QEMU TCG plugins provide a way for users to run experiments taking advantage of the total system control emulation can have over a guest. It provides a mechanism for plugins to subscribe to events during translation and execution and optionally callback into the plugin during these events. TCG plugins are unable to change the system state only monitor it passively. However they can do this down to an individual instruction granularity including potentially subscribing to all load and store operations.

API Stability¶

This is a new feature for QEMU and it does allow people to develop out-of-tree plugins that can be dynamically linked into a running QEMU process. However the project reserves the right to change or break the API should it need to do so. The best way to avoid this is to submit your plugin upstream so they can be updated if/when the API changes.

API versioning¶

All plugins need to declare a symbol which exports the plugin API version they were built against. This can be done simply by:

QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION;

The core code will refuse to load a plugin that doesn’t export a qemu_plugin_version symbol or if plugin version is outside of QEMU’s supported range of API versions.

Additionally the qemu_info_t structure which is passed to the qemu_plugin_install method of a plugin will detail the minimum and current API versions supported by QEMU. The API version will be incremented if new APIs are added. The minimum API version will be incremented if existing APIs are changed or removed.

Exposure of QEMU internals¶

The plugin architecture actively avoids leaking implementation details about how QEMU’s translation works to the plugins. While there are conceptions such as translation time and translation blocks the details are opaque to plugins. The plugin is able to query select details of instructions and system configuration only through the exported qemu_plugin functions.

Query Handle Lifetime¶

Each callback provides an opaque anonymous information handle which can usually be further queried to find out information about a translation, instruction or operation. The handles themselves are only valid during the lifetime of the callback so it is important that any information that is needed is extracted during the callback and saved by the plugin.

API¶

type qemu_plugin_id_t¶: Unique plugin ID

struct qemu_info_t¶: system information for plugins

Definition

struct qemu_info_t {
  const char *target_name;
  struct {
    int min;
    int cur;
  } version;
  bool system_emulation;
  union {
    struct {
      int smp_vcpus;
      int max_vcpus;
    } system;
  };
};

Members

target_name: string describing architecture
version: minimum and current plugin API level
system_emulation: is this a full system emulation?
{unnamed_union}: anonymous
system: information relevant to system emulation

Description

This structure provides for some limited information about the system to allow the plugin to make decisions on how to proceed. For example it might only be suitable for running on some guest architectures or when under full system emulation.

int qemu_plugin_install(qemu_plugin_id_t id, const qemu_info_t *info, int argc, char **argv)¶: Install a plugin

Parameters

qemu_plugin_id_t id: this plugin’s opaque ID
const qemu_info_t *info: a block describing some details about the guest
int argc: number of arguments
char **argv: array of arguments (argc elements)

Description

All plugins must export this symbol which is called when the plugin is first loaded. Calling qemu_plugin_uninstall() from this function is a bug.

Note

info is only live during the call. Copy any information we want to keep. argv remains valid throughout the lifetime of the loaded plugin.

Return

0 on successful loading, !0 for an error.

qemu_plugin_simple_cb_t¶: Typedef: simple callback

Syntax

void qemu_plugin_simple_cb_t (qemu_plugin_id_t id)

Parameters

qemu_plugin_id_t id: the unique qemu_plugin_id_t

Description

This callback passes no information aside from the unique id.

qemu_plugin_udata_cb_t¶: Typedef: callback with user data

Syntax

void qemu_plugin_udata_cb_t (qemu_plugin_id_t id, void *userdata)

Parameters

qemu_plugin_id_t id: the unique qemu_plugin_id_t
void *userdata: a pointer to some user data supplied when the callback was registered.

qemu_plugin_vcpu_simple_cb_t¶: Typedef: vcpu callback

Syntax

void qemu_plugin_vcpu_simple_cb_t (qemu_plugin_id_t id, unsigned int vcpu_index)

Parameters

qemu_plugin_id_t id: the unique qemu_plugin_id_t
unsigned int vcpu_index: the current vcpu context

qemu_plugin_vcpu_udata_cb_t¶: Typedef: vcpu callback

Syntax

void qemu_plugin_vcpu_udata_cb_t (unsigned int vcpu_index, void *userdata)

Parameters

unsigned int vcpu_index: the current vcpu context
void *userdata: a pointer to some user data supplied when the callback was registered.

void qemu_plugin_uninstall(qemu_plugin_id_t id, qemu_plugin_simple_cb_t cb)¶: Uninstall a plugin

Parameters

qemu_plugin_id_t id: this plugin’s opaque ID
qemu_plugin_simple_cb_t cb: callback to be called once the plugin has been removed

Description

Do NOT assume that the plugin has been uninstalled once this function returns. Plugins are uninstalled asynchronously, and therefore the given plugin receives callbacks until cb is called.

Note

Calling this function from qemu_plugin_install() is a bug.

void qemu_plugin_reset(qemu_plugin_id_t id, qemu_plugin_simple_cb_t cb)¶: Reset a plugin

Parameters

qemu_plugin_id_t id: this plugin’s opaque ID
qemu_plugin_simple_cb_t cb: callback to be called once the plugin has been reset

Description

Unregisters all callbacks for the plugin given by id.

Do NOT assume that the plugin has been reset once this function returns. Plugins are reset asynchronously, and therefore the given plugin receives callbacks until cb is called.

void qemu_plugin_register_vcpu_init_cb(qemu_plugin_id_t id, qemu_plugin_vcpu_simple_cb_t cb)¶: register a vCPU initialization callback

Parameters

qemu_plugin_id_t id: plugin ID
qemu_plugin_vcpu_simple_cb_t cb: callback function

Description

The cb function is called every time a vCPU is initialized.

See also: qemu_plugin_register_vcpu_exit_cb()

void qemu_plugin_register_vcpu_exit_cb(qemu_plugin_id_t id, qemu_plugin_vcpu_simple_cb_t cb)¶: register a vCPU exit callback

Parameters

qemu_plugin_id_t id: plugin ID
qemu_plugin_vcpu_simple_cb_t cb: callback function

Description

The cb function is called every time a vCPU exits.

See also: qemu_plugin_register_vcpu_init_cb()

void qemu_plugin_register_vcpu_idle_cb(qemu_plugin_id_t id, qemu_plugin_vcpu_simple_cb_t cb)¶: register a vCPU idle callback

Parameters

qemu_plugin_id_t id: plugin ID
qemu_plugin_vcpu_simple_cb_t cb: callback function

Description

The cb function is called every time a vCPU idles.

void qemu_plugin_register_vcpu_resume_cb(qemu_plugin_id_t id, qemu_plugin_vcpu_simple_cb_t cb)¶: register a vCPU resume callback

Parameters

qemu_plugin_id_t id: plugin ID
qemu_plugin_vcpu_simple_cb_t cb: callback function

Description

The cb function is called every time a vCPU resumes execution.

enum qemu_plugin_cb_flags¶: type of callback

Constants

QEMU_PLUGIN_CB_NO_REGS: callback does not access the CPU’s regs
QEMU_PLUGIN_CB_R_REGS: callback reads the CPU’s regs
QEMU_PLUGIN_CB_RW_REGS: callback reads and writes the CPU’s regs

Note

currently unused, plugins cannot read or change system register state.

qemu_plugin_vcpu_tb_trans_cb_t¶: Typedef: translation callback

Syntax

void qemu_plugin_vcpu_tb_trans_cb_t (qemu_plugin_id_t id, struct qemu_plugin_tb *tb)

Parameters

qemu_plugin_id_t id: unique plugin id
struct qemu_plugin_tb *tb: opaque handle used for querying and instrumenting a block.

void qemu_plugin_register_vcpu_tb_trans_cb(qemu_plugin_id_t id, qemu_plugin_vcpu_tb_trans_cb_t cb)¶: register a translate cb

Parameters

qemu_plugin_id_t id: plugin ID
qemu_plugin_vcpu_tb_trans_cb_t cb: callback function

Description

The cb function is called every time a translation occurs. The cb function is passed an opaque qemu_plugin_type which it can query for additional information including the list of translated instructions. At this point the plugin can register further callbacks to be triggered when the block or individual instruction executes.

void qemu_plugin_register_vcpu_tb_exec_cb(struct qemu_plugin_tb *tb, qemu_plugin_vcpu_udata_cb_t cb, enum qemu_plugin_cb_flags flags, void *userdata)¶: register execution callback

Parameters

struct qemu_plugin_tb *tb: the opaque qemu_plugin_tb handle for the translation
qemu_plugin_vcpu_udata_cb_t cb: callback function
enum qemu_plugin_cb_flags flags: does the plugin read or write the CPU’s registers?
void *userdata: any plugin data to pass to the cb?

Description

The cb function is called every time a translated unit executes.

enum qemu_plugin_op¶: describes an inline op

Constants

QEMU_PLUGIN_INLINE_ADD_U64: add an immediate value uint64_t

Note

currently only a single inline op is supported.

void qemu_plugin_register_vcpu_tb_exec_inline(struct qemu_plugin_tb *tb, enum qemu_plugin_op op, void *ptr, uint64_t imm)¶: execution inline op

Parameters

struct qemu_plugin_tb *tb: the opaque qemu_plugin_tb handle for the translation
enum qemu_plugin_op op: the type of qemu_plugin_op (e.g. ADD_U64)
void *ptr: the target memory location for the op
uint64_t imm: the op data (e.g. 1)

Description

Insert an inline op to every time a translated unit executes. Useful if you just want to increment a single counter somewhere in memory.

Note

ops are not atomic so in multi-threaded/multi-smp situations you will get inexact results.

void qemu_plugin_register_vcpu_insn_exec_cb(struct qemu_plugin_insn *insn, qemu_plugin_vcpu_udata_cb_t cb, enum qemu_plugin_cb_flags flags, void *userdata)¶: register insn execution cb

Parameters

struct qemu_plugin_insn *insn: the opaque qemu_plugin_insn handle for an instruction
qemu_plugin_vcpu_udata_cb_t cb: callback function
enum qemu_plugin_cb_flags flags: does the plugin read or write the CPU’s registers?
void *userdata: any plugin data to pass to the cb?

Description

The cb function is called every time an instruction is executed

void qemu_plugin_register_vcpu_insn_exec_inline(struct qemu_plugin_insn *insn, enum qemu_plugin_op op, void *ptr, uint64_t imm)¶: insn execution inline op

Parameters

struct qemu_plugin_insn *insn: the opaque qemu_plugin_insn handle for an instruction
enum qemu_plugin_op op: the type of qemu_plugin_op (e.g. ADD_U64)
void *ptr: the target memory location for the op
uint64_t imm: the op data (e.g. 1)

Description

Insert an inline op to every time an instruction executes. Useful if you just want to increment a single counter somewhere in memory.

size_t qemu_plugin_tb_n_insns(const struct qemu_plugin_tb *tb)¶: query helper for number of insns in TB

Parameters

const struct qemu_plugin_tb *tb: opaque handle to TB passed to callback

Return

number of instructions in this block

uint64_t qemu_plugin_tb_vaddr(const struct qemu_plugin_tb *tb)¶: query helper for vaddr of TB start

Parameters

const struct qemu_plugin_tb *tb: opaque handle to TB passed to callback

Return

virtual address of block start

struct qemu_plugin_insn *qemu_plugin_tb_get_insn(const struct qemu_plugin_tb *tb, size_t idx)¶: retrieve handle for instruction

Parameters

const struct qemu_plugin_tb *tb: opaque handle to TB passed to callback
size_t idx: instruction number, 0 indexed

Description

The returned handle can be used in follow up helper queries as well as when instrumenting an instruction. It is only valid for the lifetime of the callback.

Return

opaque handle to instruction

const void *qemu_plugin_insn_data(const struct qemu_plugin_insn *insn)¶: return ptr to instruction data

Parameters

const struct qemu_plugin_insn *insn: opaque instruction handle from qemu_plugin_tb_get_insn()

Note

data is only valid for duration of callback. See qemu_plugin_insn_size() to calculate size of stream.

Return

pointer to a stream of bytes containing the value of this instructions opcode.

size_t qemu_plugin_insn_size(const struct qemu_plugin_insn *insn)¶: return size of instruction

Parameters

const struct qemu_plugin_insn *insn: opaque instruction handle from qemu_plugin_tb_get_insn()

Return

size of instruction in bytes

uint64_t qemu_plugin_insn_vaddr(const struct qemu_plugin_insn *insn)¶: return vaddr of instruction

Parameters

const struct qemu_plugin_insn *insn: opaque instruction handle from qemu_plugin_tb_get_insn()

Return

virtual address of instruction

void *qemu_plugin_insn_haddr(const struct qemu_plugin_insn *insn)¶: return hardware addr of instruction

Parameters

const struct qemu_plugin_insn *insn: opaque instruction handle from qemu_plugin_tb_get_insn()

Return

hardware (physical) target address of instruction

type qemu_plugin_meminfo_t¶: opaque memory transaction handle

Description

This can be further queried using the qemu_plugin_mem_* query functions.

unsigned int qemu_plugin_mem_size_shift(qemu_plugin_meminfo_t info)¶: get size of access

Parameters

qemu_plugin_meminfo_t info: opaque memory transaction handle

Return

size of access in ^2 (0=byte, 1=16bit, 2=32bit etc…)

bool qemu_plugin_mem_is_sign_extended(qemu_plugin_meminfo_t info)¶: was the access sign extended

Parameters

qemu_plugin_meminfo_t info: opaque memory transaction handle

Return

true if it was, otherwise false

bool qemu_plugin_mem_is_big_endian(qemu_plugin_meminfo_t info)¶: was the access big endian

Parameters

qemu_plugin_meminfo_t info: opaque memory transaction handle

Return

true if it was, otherwise false

bool qemu_plugin_mem_is_store(qemu_plugin_meminfo_t info)¶: was the access a store

Parameters

qemu_plugin_meminfo_t info: opaque memory transaction handle

Return

true if it was, otherwise false

struct qemu_plugin_hwaddr *qemu_plugin_get_hwaddr(qemu_plugin_meminfo_t info, uint64_t vaddr)¶: return handle for memory operation

Parameters

qemu_plugin_meminfo_t info: opaque memory info structure
uint64_t vaddr: the virtual address of the memory operation

Description

For system emulation returns a qemu_plugin_hwaddr handle to query details about the actual physical address backing the virtual address. For linux-user guests it just returns NULL.

This handle is only valid for the duration of the callback. Any information about the handle should be recovered before the callback returns.

bool qemu_plugin_hwaddr_is_io(const struct qemu_plugin_hwaddr *haddr)¶: query whether memory operation is IO

Parameters

const struct qemu_plugin_hwaddr *haddr: address handle from qemu_plugin_get_hwaddr()

Description

Returns true if the handle’s memory operation is to memory-mapped IO, or false if it is to RAM

uint64_t qemu_plugin_hwaddr_phys_addr(const struct qemu_plugin_hwaddr *haddr)¶: query physical address for memory operation

Parameters

const struct qemu_plugin_hwaddr *haddr: address handle from qemu_plugin_get_hwaddr()

Description

Returns the physical address associated with the memory operation

Note that the returned physical address may not be unique if you are dealing with multiple address spaces.

char *qemu_plugin_insn_disas(const struct qemu_plugin_insn *insn)¶: return disassembly string for instruction

Parameters

const struct qemu_plugin_insn *insn: instruction reference

Description

Returns an allocated string containing the disassembly

void qemu_plugin_vcpu_for_each(qemu_plugin_id_t id, qemu_plugin_vcpu_simple_cb_t cb)¶: iterate over the existing vCPU

Parameters

qemu_plugin_id_t id: plugin ID
qemu_plugin_vcpu_simple_cb_t cb: callback function

Description

The cb function is called once for each existing vCPU.

See also: qemu_plugin_register_vcpu_init_cb()

void qemu_plugin_outs(const char *string)¶: output string via QEMU’s logging system

Parameters

const char *string: a string

Usage¶

The QEMU binary needs to be compiled for plugin support:

configure --enable-plugins

Once built a program can be run with multiple plugins loaded each with their own arguments:

$QEMU $OTHER_QEMU_ARGS \
    -plugin tests/plugin/libhowvec.so,arg=inline,arg=hint \
    -plugin tests/plugin/libhotblocks.so

Arguments are plugin specific and can be used to modify their behaviour. In this case the howvec plugin is being asked to use inline ops to count and break down the hint instructions by type.

Plugin Life cycle¶

First the plugin is loaded and the public qemu_plugin_install function is called. The plugin will then register callbacks for various plugin events. Generally plugins will register a handler for the atexit if they want to dump a summary of collected information once the program/system has finished running.

When a registered event occurs the plugin callback is invoked. The callbacks may provide additional information. In the case of a translation event the plugin has an option to enumerate the instructions in a block of instructions and optionally register callbacks to some or all instructions when they are executed.

There is also a facility to add an inline event where code to increment a counter can be directly inlined with the translation. Currently only a simple increment is supported. This is not atomic so can miss counts. If you want absolute precision you should use a callback which can then ensure atomicity itself.

Finally when QEMU exits all the registered atexit callbacks are invoked.

Internals¶

Locking¶

We have to ensure we cannot deadlock, particularly under MTTCG. For this we acquire a lock when called from plugin code. We also keep the list of callbacks under RCU so that we do not have to hold the lock when calling the callbacks. This is also for performance, since some callbacks (e.g. memory access callbacks) might be called very frequently.

A consequence of this is that we keep our own list of CPUs, so that we do not have to worry about locking order wrt cpu_list_lock.

Use a recursive lock, since we can get registration calls from callbacks.

As a result registering/unregistering callbacks is “slow”, since it takes a lock. But this is very infrequent; we want performance when calling (or not calling) callbacks, not when registering them. Using RCU is great for this.

We support the uninstallation of a plugin at any time (e.g. from plugin callbacks). This allows plugins to remove themselves if they no longer want to instrument the code. This operation is asynchronous which means callbacks may still occur after the uninstall operation is requested. The plugin isn’t completely uninstalled until the safe work has executed while all vCPUs are quiescent.

Example Plugins¶

There are a number of plugins included with QEMU and you are encouraged to contribute your own plugins plugins upstream. There is a contrib/plugins directory where they can go.

tests/plugins

These are some basic plugins that are used to test and exercise the API during the make check-tcg target.

contrib/plugins/hotblocks.c

The hotblocks plugin allows you to examine the where hot paths of execution are in your program. Once the program has finished you will get a sorted list of blocks reporting the starting PC, translation count, number of instructions and execution count. This will work best with linux-user execution as system emulation tends to generate re-translations as blocks from different programs get swapped in and out of system memory.

If your program is single-threaded you can use the inline option for slightly faster (but not thread safe) counters.

Example:

./aarch64-linux-user/qemu-aarch64 \
  -plugin contrib/plugins/libhotblocks.so -d plugin \
  ./tests/tcg/aarch64-linux-user/sha1
SHA1=15dd99a1991e0b3826fede3deffc1feba42278e6
collected 903 entries in the hash table
pc, tcount, icount, ecount
0x0000000041ed10, 1, 5, 66087
0x000000004002b0, 1, 4, 66087
...

contrib/plugins/hotpages.c

Similar to hotblocks but this time tracks memory accesses:

./aarch64-linux-user/qemu-aarch64 \
  -plugin contrib/plugins/libhotpages.so -d plugin \
  ./tests/tcg/aarch64-linux-user/sha1
SHA1=15dd99a1991e0b3826fede3deffc1feba42278e6
Addr, RCPUs, Reads, WCPUs, Writes
0x000055007fe000, 0x0001, 31747952, 0x0001, 8835161
0x000055007ff000, 0x0001, 29001054, 0x0001, 8780625
0x00005500800000, 0x0001, 687465, 0x0001, 335857
0x0000000048b000, 0x0001, 130594, 0x0001, 355
0x0000000048a000, 0x0001, 1826, 0x0001, 11

contrib/plugins/howvec.c

This is an instruction classifier so can be used to count different types of instructions. It has a number of options to refine which get counted. You can give an argument for a class of instructions to break it down fully, so for example to see all the system registers accesses:

./aarch64-softmmu/qemu-system-aarch64 $(QEMU_ARGS) \
  -append "root=/dev/sda2 systemd.unit=benchmark.service" \
  -smp 4 -plugin ./contrib/plugins/libhowvec.so,arg=sreg -d plugin

which will lead to a sorted list after the class breakdown:

Instruction Classes:
Class:   UDEF                   not counted
Class:   SVE                    (68 hits)
Class:   PCrel addr             (47789483 hits)
Class:   Add/Sub (imm)          (192817388 hits)
Class:   Logical (imm)          (93852565 hits)
Class:   Move Wide (imm)        (76398116 hits)
Class:   Bitfield               (44706084 hits)
Class:   Extract                (5499257 hits)
Class:   Cond Branch (imm)      (147202932 hits)
Class:   Exception Gen          (193581 hits)
Class:     NOP                  not counted
Class:   Hints                  (6652291 hits)
Class:   Barriers               (8001661 hits)
Class:   PSTATE                 (1801695 hits)
Class:   System Insn            (6385349 hits)
Class:   System Reg             counted individually
Class:   Branch (reg)           (69497127 hits)
Class:   Branch (imm)           (84393665 hits)
Class:   Cmp & Branch           (110929659 hits)
Class:   Tst & Branch           (44681442 hits)
Class:   AdvSimd ldstmult       (736 hits)
Class:   ldst excl              (9098783 hits)
Class:   Load Reg (lit)         (87189424 hits)
Class:   ldst noalloc pair      (3264433 hits)
Class:   ldst pair              (412526434 hits)
Class:   ldst reg (imm)         (314734576 hits)
Class: Loads & Stores           (2117774 hits)
Class: Data Proc Reg            (223519077 hits)
Class: Scalar FP                (31657954 hits)
Individual Instructions:
Instr: mrs x0, sp_el0           (2682661 hits)  (op=0xd5384100/  System Reg)
Instr: mrs x1, tpidr_el2        (1789339 hits)  (op=0xd53cd041/  System Reg)
Instr: mrs x2, tpidr_el2        (1513494 hits)  (op=0xd53cd042/  System Reg)
Instr: mrs x0, tpidr_el2        (1490823 hits)  (op=0xd53cd040/  System Reg)
Instr: mrs x1, sp_el0           (933793 hits)   (op=0xd5384101/  System Reg)
Instr: mrs x2, sp_el0           (699516 hits)   (op=0xd5384102/  System Reg)
Instr: mrs x4, tpidr_el2        (528437 hits)   (op=0xd53cd044/  System Reg)
Instr: mrs x30, ttbr1_el1       (480776 hits)   (op=0xd538203e/  System Reg)
Instr: msr ttbr1_el1, x30       (480713 hits)   (op=0xd518203e/  System Reg)
Instr: msr vbar_el1, x30        (480671 hits)   (op=0xd518c01e/  System Reg)
...

To find the argument shorthand for the class you need to examine the source code of the plugin at the moment, specifically the *opt argument in the InsnClassExecCount tables.

contrib/plugins/lockstep.c

This is a debugging tool for developers who want to find out when and where execution diverges after a subtle change to TCG code generation. It is not an exact science and results are likely to be mixed once asynchronous events are introduced. While the use of -icount can introduce determinism to the execution flow it doesn’t always follow the translation sequence will be exactly the same. Typically this is caused by a timer firing to service the GUI causing a block to end early. However in some cases it has proved to be useful in pointing people at roughly where execution diverges. The only argument you need for the plugin is a path for the socket the two instances will communicate over:

./sparc-softmmu/qemu-system-sparc -monitor none -parallel none \
  -net none -M SS-20 -m 256 -kernel day11/zImage.elf \
  -plugin ./contrib/plugins/liblockstep.so,arg=lockstep-sparc.sock \
-d plugin,nochain

which will eventually report:

qemu-system-sparc: warning: nic lance.0 has no peer
@ 0x000000ffd06678 vs 0x000000ffd001e0 (2/1 since last)
@ 0x000000ffd07d9c vs 0x000000ffd06678 (3/1 since last)
Δ insn_count @ 0x000000ffd07d9c (809900609) vs 0x000000ffd06678 (809900612)
  previously @ 0x000000ffd06678/10 (809900609 insns)
  previously @ 0x000000ffd001e0/4 (809900599 insns)
  previously @ 0x000000ffd080ac/2 (809900595 insns)
  previously @ 0x000000ffd08098/5 (809900593 insns)
  previously @ 0x000000ffd080c0/1 (809900588 insns)

contrib/plugins/hwprofile

The hwprofile tool can only be used with system emulation and allows the user to see what hardware is accessed how often. It has a number of options:

arg=read or arg=write

By default the plugin tracks both reads and writes. You can use one of these options to limit the tracking to just one class of accesses.

arg=source

Will include a detailed break down of what the guest PC that made the access was. Not compatible with arg=pattern. Example output:
cirrus-low-memory @ 0xfffffd00000a0000
 pc:fffffc0000005cdc, 1, 256
 pc:fffffc0000005ce8, 1, 256
 pc:fffffc0000005cec, 1, 256
arg=pattern

Instead break down the accesses based on the offset into the HW region. This can be useful for seeing the most used registers of a device. Example output:
pci0-conf @ 0xfffffd01fe000000
  off:00000004, 1, 1
  off:00000010, 1, 3
  off:00000014, 1, 3
  off:00000018, 1, 2
  off:0000001c, 1, 2
  off:00000020, 1, 2
  ...