OProfile JIT agent developer guide
Maynard
Johnson
maynardj@us.ibm.com
2007
IBM Corporation
Developing a new JIT agent
OProfile includes a header file and library that are intended to be used by
developers who wish to extend OProfile's JIT support to other non-supported
virtual machines. This developer guide describes these development files and how
to use them.
Overview
OProfile already includes some implementations that use the JIT support,
e.g., the Java Virtual Machine Toolkit Interface (JVMTI) library,
libjvmti_oprofile.so. In developing a new implementation, you will
likely follow a similar (if not identical) procedure as was used in
developing the JVMTI library. Following are the high level steps to follow:
Ensure your virtual machine provides an API that, at minimum,
can provide the following information about dynamically compiled code:
Notification when compilation occurs
Name of the symbol (i.e., function or class/method, etc.)
Address in anonymous memory where the compiled code was loaded
Length of the compiled code segment
Write an agent library that communicates with your VM to obtain
compiled code notifications. Invoke the required functions from opagent.h
() and link your library with libopagent.so
(installed at <oprofile_install_dir>/lib/oprofile).
Implementing JIT support for a new virtual machine
The JIT support API for OProfile is defined
in <oprofile-install-dir>/include/opagent.h.
Some parts of the API are mandatory for an agent library to use; other
parts are optional. The mandatory functions are shown below.
op_agent_t op_open_agent(void);
void op_close_agent(op_agent_t hdl);
int op_write_native_code(op_agent_t hdl, char const * symbol_name,
uint64_t vma, const void * code,
const unsigned int code_size);
To implement this part of your library, you must perform the
following steps:
Implement a function to set up initial communication with the VM.
Once communication to the VM is established, your agent library should call
op_op_agent() and cache the returned op_agent_t
handle for use in
future calls.
Perform any necessary steps to register with the VM to be notified of
compiled code load events. Registration must include a callback function you
will implement in the library to handle the compiled code load events.
The callback function mentioned above must obtain all required
information from the VM to pass to libopagent via op_write_native_code().
When disconnecting from the VM, your library should call
op_agent_close().
Use of the functions below are optional, depending on the kinds of information your VM
can provide to your agent library. See the JVMTI agent library for an example of how to use
these functions.
int op_unload_native_code(op_agent_t hdl, uint64_t vma);
int op_write_debug_line_info(op_agent_t hdl, void const * code,
size_t nr_entry,
struct debug_line_info const * compile_map);
While the libopagent functions are thread-safe, you should not use them in
signal handlers.
The JIT support API
This chapter describes the JIT support API. See opagent.h for more details.
op_open_agent
Initializes the agent library.
#include <opagent.h>
op_agent_t op_open_agent
void
Description
This function must be called by agents before any other function.
Creates and opens a JIT dump file in /var/lib/oprofile/jitdump
using the naming convention <process_id>.dump.
Parameters
None
Return value
Returns a valid op_agent_t
handle or NULL.
If NULL is returned, errno
is set to indicate the nature of the error. For a list
of possible errno
values, see the man pages for:
stat, creat, gettimeofday, fdopen, fwrite
op_close_agent
Uninitialize the agent library.
#include <opagent.h>
int op_close_agent
op_agent_t hdl
Description
Frees all resources and closes open file handles.
Parameters
hdl : Handle returned from an earlier call to
op_open_agent()
Return value
Returns 0 on success; -1 otherwise. If -1 is returned, errno
is set
to indicate the nature of the error.
errno
is set to EINVAL if an invalid op_agent_t
handle is passed. For a list of other possible errno
values, see the man pages for:
gettimeofday, fwrite
op_write_native_code
Write information about compiled code to a JIT dump file.
#include <opagent.h>
int op_write_native_code
op_agent_thdl
char const *symbol_name
uint64_tvma
void const *code
const unsigned intcode_size
Description
Signal the dynamic generation of native code from a virtual machine.
Writes a JIT dump record to the open JIT dump file using the passed information.
Parameters
hdl : Handle returned from an earlier call to
op_open_agent()
symbol_name : The name of the symbol being dynamically compiled.
This name can (and should) contain all necessary information to disambiguate it from
symbols of the same name; e.g., class, method signature.
vma : Virtual memory address of the executable code
code : Pointer to the location of the compiled code.
Theoretically, this may be a different location from
that given by the vma argument. For some JIT compilers,
obtaining the code may be impractical. For this (or any other)
reason, the agent can choose to pass NULL for this paraemter.
If NULL is passed, no code will be copied into the JIT dump
file.
code_size : Size of the compiled code
Return value
Returns 0 on success; -1 otherwise. If -1 is returned, errno
is set
to indicate the nature of the error.
errno
is set to EINVAL if an invalid op_agent_t
handle is passed. For a list of other possible errno
values, see the man pages for:
gettimeofday, fwrite
op_write_debug_line_info
Write debug information about compiled code to a JIT dump file.
#include <opagent.h>
int op_write_debug_line_info
op_agent_thdl
void const *code
size_tnr_entry
struct debug_line_info const *compile_map
Description
Add debug line information to a piece of code. An op_write_native_code()
with the same code pointer should have occurred before this call. It's not
necessary to provide one lineno information entry per machine instruction;
the array can contain hole.
Parameters
hdl : Handle returned from an earlier call to
op_open_agent()
code : Pointer to the location of the code with debug info
nr_entry : Number of entries in compile_map
compile_map : Array of struct debug_line_info. See the JVMTI agent
library implementation for an example of what information should be retrieved
from a VM to fill out this data structure.
Return value
Returns 0 on success; -1 otherwise. If -1 is returned, errno
is set
to indicate the nature of the error.
errno
is set to EINVAL if an invalid op_agent_t
handle is passed. For a list of other possible errno
values, see the man pages for:
gettimeofday, ftell, fwrite
op_unload_native_code
Write information to the JIT dump file about invalidated compiled code.
#include <opagent.h>
int op_unload_native_code
op_agent_thdl
uint64_tvma
Description
Signal the invalidation of native code from a virtual machine.
Parameters
hdl : Handle returned from an earlier call to
op_open_agent()
vma : Virtual memory address of the compiled code being unloaded.
An op_write_native_code() with the same vma should have occurred before this call.
Return value
Returns 0 on success; -1 otherwise. If -1 is returned, errno
is set
to indicate the nature of the error.
errno
is set to EINVAL if an invalid op_agent_t
handle is passed. For a list of other possible errno
values, see the man pages for:
gettimeofday, fwrite