The mkimage System Image
This section contains more information on the output from the mkimage tool and the target-specific configuration files that are described in the previous section.
Relocating ELF Files
If relocation is specified for a given file, mkimage relocates it and stores the resulting absolute binary file in the memory bank. You can specify how many program segments must contain the resulting binary file and, for each individual segment, how it must be relocated.
A segment can be relocated to a linking area or to the segment image's base address within the memory bank.
A linking area is a named range of addresses specified by an id, a base address, and a size. You can specify a different linking area for each program segment. mkimage relocates a segment to the lowest available range of addresses of a suitable size within the linking area. mkimage guarantees that different segments relocated to the same linking area will never overlap. However, segments relocated to private linking areas can overlap.
Execution in Place (XIP)
For any particular segment you can specify whether the segment must be executed at its place within the memory bank (in this document this segment is refered to as the "XIP segment") or whether it must be copied into the RAM before it is executed.
bootconf Binary
The mkimage command builds a binary file called bootconf. The bootconf file contains a data structure called BootConf, which describes the system image contents and layout. mkimage includes the bootconf binary file in one of the system image memory banks.
The initial loader boots the ChorusOS operating system, jumping to the entry point of the bootconf binary (see "Overview" for more details).
bootconf is a board-independent program that gets control from the board-specific initial loader and transfers control to the board-specific bootstrap program. In some cases, the initial loader needs to pass a board-dependent parameter to the bootstrap. This parameter can be loaded into a specific CPU register, and bootconf passes the entry value of the register to the bootstrap program as an opaque parameter. The register is:
When the bootconf binary is entered, it sets up a program stack in a stack area within its data segment, finds the descriptor of the bootstrap binary in the BootConf structure, and jumps to this entry point, passing the following parameters:
-
The address of the BootConf structure
-
An opaque value from the initial loader
To jump to the bootstrap entry point, bootconf uses the standard C function invocation conventions. The bootstrap entry point is:
typedef void (*BootEntry) (struct BootConf*, void* cookie);
BootConf Structure
The bootconf file contains an object of type BootConf and all the objects it points to. It describes the structure of the system image in terms of its components.
typedef struct BootConf {
unsigned int stamp; /* identification stamp */
PhMap* kernelSpace; /* initial address space
descriptor */
VmAddr spaceBarrier; /* frontier between user and
supervisor address space */
int numBanks; /* number of system image memory
banks */
BankDesc* bankDesc; /* system image memory bank
descriptors */
int numBins; /* number of binaries */
BinDesc* binDesc; /* array of binary descriptors */
int numSegs; /* number of segments */
BinSegDesc* segDesc; /* array of segment descriptors */
RamDesc ramAllocator; /* ram occupation */
KnSymbolTable* symbols; /* symbols for kdb */
EnvDesc* env; /* environment descriptor */
void* heapStart; /* memory heap: */
void* heapCur; /* occupied from heapStart to
heapCur */
void* heapLimit; /* available from heapCur to
heapLimit */
unsigned int siteNumber; /* site number used for remote
IPC */
DevNode rootDevice; /* device tree */
IdleFunc idleFunc; /* function to be executed in the
idle loop */
DbgBsp dbgBsp; /* bsp for Debug Agent */
DbgOps dbgOps; /* debug Agent interface */
BootConfRebootEntry rebootEntry; /* reboot entry */
RebootDesc* rebootDesc; /* reboot descriptor */
void* f_bootConf; /* a processor-specific
descriptor */
} BootConf;
Code Example 7-11 contains an example of a BootConf structure.
The Initial Address Space
The kernelSpace field describes the initial address space. The exact interpretation of this descriptor is architecture dependent:
-
In some cases, kernelSpace describes the address space which must be established in the hardware when entering the microkernel.
-
In other cases, kernelSpace describes the address space which must be established by the microkernel's memory management module.
-
Some architectures do not require kernelSpace at all (for example when there is no MMU).
Other architecture-dependent requirements for the initial address space layout may be specified. See "The Boot-Kernel Interface" for details.
If required, the initial virtual address space is specified by the PhMap structure:
typedef struct PhChunk {
PhAddr start; /* chunk physical start address */
PhSize size; /* chunk size in bytes */
unsigned int tag; /* chunk attributes */
} PhChunk;
typedef struct PhMap {
int numChunks; /* number of items in the array */
PhChunk* chunk; /* array of chunk descriptors */
} PhMap;
PhMap and PhChunk
are declared in source_dir/nucleus/sys/common/src/kern/bki/phMap.h and source_dir/nucleus/sys/common/src/kern/bki/phChunk.h respectively. The PhMap structure is
a series of PhChunk entries, each entry describing the virtual-to-physical
translation of a contiguous range of virtual addresses. The size field of
a PhChunk descriptor indicates the size of the range. The starting
address of the range is given by the sum of the size values of the previous
ranges. Therefore, the PhMap structure must describe
the entire virtual address space.
If the tag value in PhChunk
is equal to KSP_INVALID the translation is invalid and
access to any address in the range described by PhChunk is prohibited.
Otherwise, the start field of a PhChunk structure gives the starting address of the physical address range
that the virtual address is mapped to. The tag
field of a PhChunk structure specifies the attributes
associated with the mapping. The highest 24 bits of tag are used to store architecture-dependent attribute sets,
such as memory access rights and cache control. See "The Boot-Kernel Interface"
for details of architecture-specific BKI. The lowest 8 bits are reserved for
use by the microkernel, and are set to 0 by mkimage.
The value of the spaceBarrier field may influence the dimensions of the supervisor and the user virtual address spaces. The exact meaning of this field is architecture dependent.
Banks
The bankDesc structure points to an array of BankDesc system image memory
bank descriptors.
typedef struct BankDesc {
char* id; /* bank's symbolic name */
BankType type; /* bank's type */
char* fs; /* files system type symbolic name */
VmAddr vaddr; /* address required for the bank's image */
VmSize size; /* bank's size */
} BankDesc;
The bankDesc structure is declared in source_dir/nucleus/sys/common/src/kern/bki/bki.h. A memory bank is specified by vaddr, indicating the starting address within the initial address space, and size.
The type field value is a combination of the bits listed in Table 7-1.
Table 7-1 type Bits| type Bit | Meaning |
|---|---|
| BANK_KSP | always "1" in this version |
| BANK_DEVICE | bank is a memory device |
| BANK_DEVICE_READ | data from the memory device can be read |
| BANK_DEVICE_WRITE | data from the memory device can be modified |
| BANK_DEVICE_EXEC | instructions from the memory device can be executed |
If any of the last three bits is set, the BANK_DEVICE bit must also be set.
Files in a memory bank can be organized as a volume of a file system. In this case, the fs field points to a string containing the name of the file system type (for example, "FAT" stands for MS-DOS FAT file system). Otherwise, fs is 0.
When the initial loader jumps to the bootconf entry point, the memory banks containing the BIN_BOOTCONF and BIN_BOOTSTRAP program binaries must already be installed at the address indicated by vaddr.
When the bootstrap program transfers control to the microkernel, all memory banks must be installed at the address indicated by vaddr.
Binaries
The binDesc array points to an array of BinDesc structures. Each structure describes an absolute executable binary
involved in the system deployment procedure, such as a bootconf,
bootstrap, microkernel, or a driver. These binaries are part of the system
image.
typedef struct BinDesc {
char* name; /* binary symbolic name */
int firstSeg; /* first segment index */
int lastSeg; /* last segment index */
KnPc entry; /* binary entry point */
BinType type; /* binary type */
BinMode mode; /* binary loading mode */
void* actor; /* private for the u-kernel */
} BinDesc;
Each binary is composed of a set of segments. The firstSeg and lastSeg fields specify the range
of segments within the array of segment descriptors, pointed to by segDesc, that store the binary described by BinDesc.
The type field specifies the binary's type and is set to one of the binType values listed in Table 7-2.
Table 7-2binType ValuesBinType Value | Type of Binary |
|---|---|
| BIN_BOOTCONF | bootconf program |
| BIN_BOOTSTRAP | bootstrap program |
| BIN_REBOOT | reboot program |
| BIN_DBG_AGENT | system debug agent |
| BIN_DBG_DRIVER | debug agent communication driver |
| BIN_KERNEL | microkernel |
| BIN_DRIVER | a ChorusOS device driver |
| BIN_SUPERVISOR | a supervisor actor |
| BIN_USER | a user actor |
BinType values are defined in such a way that:
-
The BIN_STANDALONE bit is 1 in, and only in, BIN_BOOTSTRAP, BIN_DBG_AGENT, and BIN_DBG_DRIVER.
-
The BIN_ACTOR bit is 1 in, and only in, BIN_DRIVER, BIN_SUPERVISOR, and BIN_USER.
-
The BIN_KERNEL bit is 1 in, and only in, BIN_KERNEL.
The mode specifies the binary activation mode and can be any combination of the BinMode flags listed in Table 7-3.
Table 7-3BinMode FlagsBinMode Flag | Meaning |
|---|---|
| BIN_DEBUGGED | The binary must be launched in debug mode. |
| BIN_STOPPED | The binary must be loaded but not started. |
These flags only have meaning for BIN_SUPERVISOR and BIN_USER binaries. The value of mode is ignored for all other binary types.
The numBins field specifies the number of elements in the array pointed to by binDesc.
segDesc points to an array of segment descriptors.
Each item in the array is a SegDesc data structure and describes
a segment of the system image. SegDesc is declared
in source_dir/nucleus/sys/common/src/kern/bki/bki.h.
typedef struct SegDesc {
VmAddr kaddr; /* image address */
VmAddr vaddr; /* execution address (from link editor) */
VmSize ksize; /* image size */
VmSize vsize; /* execution size */
SegType type; /* code or data */
SegSpace space; /* address space type */
} SegDesc;
The descriptor specifies two things:
-
The location of the segment's image
-
Where the segment must be installed for execution
The segment image is stored in the memory bank containing the segment's binary. When the memory bank is installed at the required address, as specified in the BankDesc structure, the segment image can be found at kaddr. The ksize field specifies the size of the segment image contained in the memory bank.
When executed, the segment must be installed at the address specified by the vaddr field and its size must be equal to vsize. If vsize is greater than ksize, the memory from vaddr+ksize to vaddr+vsize must be initialized to zero.
The space field indicates whether a segment belongs to the initial address space. It can be set to one of the values listed in Table 7-4.
Table 7-4SegSpace ValuesSegSpace Value | Meaning |
| SEG_KSP | segment belongs to the initial microkernel address space |
| SEG_VIRTUAL | segment does not belong to the initial microkernel address space |
Only binaries of the BIN_ACTOR type can hold SEG_VIRTUAL segments.
The value of the type field can be any combination of the bits listed in Table 7-5.
Table 7-5 SegType Bit ValuesSegType Bit | Meaning |
|---|---|
| SEG_XIP | Segment must be executed at its place in the memory bank |
| SEG_EXEC | Segment contains instructions |
| SEG_READ | Segment contains read-only data |
| SEG_WRITE | Segment contains write data |
If a segment is executable in place (XIP), and belongs to the initial kernel address space (for example, the SEG_XIP bit is set in the type field and the space field is equal to SEG_KSP), the segment's execution address will be the same as the segment's image address and the segment's execution size will be equal the segment's image size. Therefore, when a memory bank is installed at the address specified by its descriptor (BankDesc::vaddr), all XIP KSP segments that belong to the memory bank will have no particular installation procedure and will be ready for execution.
The numSegs field specifies the number of
elements in the array pointed to by SegDesc.
RAM Occupation
The ramAllocator field describes RAM occupation by the system image. The mkbootconf tool initializes the ramAllocator state. It tags as allocated the memory dedicated to:
-
All RAM based system image memory banks (see "Banks").
-
Global system control blocks (for example
CpuContextandChorusContext) that are mapped to non-virtual linking areas (see "Areas"). -
All non-XIP segments (XIP segments are contained in memory banks) that are mapped to non-virtual linking areas (see "Areas").
The ChorusOS operating system provides a library of functions to manipulate
the RamDesc objects (see "RAM Allocator interface"). RamDesc is declared in source_dir/nucleus/sys/common/src/kern/bki/ram.h. These functions allow the bootstrap program to tag any range
of physical addresses with an attribute.
Environment Variables
The env field points to an EnvDesc structure. The EnvDesc structure is declared in source_dir/nucleus/sys/common/src/lib/util/env.h.
typedef struct EnvDesc {
int envSize; /* current size of environment */
int envMaxSize; /* memory available for environment */
char* envPtr; /* pointer to the environment */
} EnvDesc;
The system image contains a data file with the initial state of the system environment variables. The env field of the BootConf structure references the contents of this file.
The envPtr field points to a sequence of environment variable definitions. Each definition is a concatenation of two strings, envVariable and envValue, where envVariable is the null-terminated string name of an environment variable, and envValue is the null-terminated string value of the environment variable.
The envSize field is the size in bytes of the environment variable definition sequence.
The envMaxSize field is the environment file size. It must not exceed envMaxSize.
Heap and Stack
The heapStart field points to the beginning of a block of statically allocated memory. The block can be used by the bootstrap program for dynamic memory allocation. For instance, the heap is used by the device tree library memory allocator (see "Initial Device Tree") to build the initial state of the board's device tree.
The heapCur field points to the first byte available for future allocation. The mkbootconf tool sets heapCur to heapStart.
The heapLimit field points to the heap memory limit. The size of the heap memory is equal to heapLimit-heapStart.
The heap is also used for the initial stack. The bootconf start-up procedure initializes the current stack pointer with the heapLimit value.
All other fields of the BootConf structure are initialized dynamically during the system bootstrap.
Example BootConf Structure
This section contains an example of a BootConf structure for the SBC8260 PPC8260 EC603e-based board.
Example 7-11 BootConf Structure
#include bki/bki.h
#include bki/f_bki.h
PhChunk __mkimage__label__kernelSpace[] = {
{ 0x0, 0x1000000, KSP_PPC60x_BAT|KSP_PPC60x_M|KSP_PPC60x_RW },
{ 0x0, 0xe000000, KSP_INVALID },
{ 0xf000000, 0x20000, KSP_PPC60x_BAT|KSP_PPC60x_G|KSP_PPC60x_I|
KSP_PPC60x_RW },
{ 0x0, 0xecfe0000, KSP_INVALID },
{ 0xfc000000, 0x4000000, KSP_PPC60x_BAT|KSP_PPC60x_RO }
};
BankDesc __mkimage__label__banks[] = {
{ "sys_bank", BANK_KSP, 0, 0x100000, 0xb3000}
};
BinDesc __mkimage__label__binDesc[] = {
{
"dbgBsp",
0,
0,
0x10042c,
BIN_DBG_DRIVER,
0 | 0
},
{
"dbgAgent",
1,
1,
0x104494,
BIN_DBG_AGENT,
0 | 0
},
{
"boot",
2,
2,
0x108000,
BIN_BOOTSTRAP,
0 | 0
},
{
"reboot",
3,
3,
0x10d27c,
BIN_REBOOT,
0 | 0
},
{
"kern",
4,
5,
0x125418,
BIN_KERNEL,
0 | 0
},
{
"D_tbDec",
6,
6,
0x186000,
BIN_DRIVER,
0 | 0
},
{
"D_quicc8260",
7,
8,
0x188000,
BIN_DRIVER,
0 | 0
},
{
"D_fccEther",
9,
9,
0x18e000,
BIN_DRIVER,
0 | 0
},
{
"PD",
10,
11,
0x195000,
BIN_SUPERVISOR,
0 | 0
},
{
"kernonly_symb",
12,
12,
0x198000,
BIN_DBG_AGENT,
0 | 0
},
{
"kernonly_bconf",
13,
13,
0x1b0000,
BIN_BOOTCONF,
0 | 0
}
};
BinSegDesc __mkimage__label__segDesc[] = {
{
0x100000,
0x100000,
0x608,
0x608,
SEG_XIP | SEG_EXEC | SEG_READ | SEG_WRITE,
SEG_KSP
},
{
0x101000,
0x101000,
0x6234,
0x6234,
SEG_XIP | SEG_EXEC | SEG_READ | SEG_WRITE,
SEG_KSP
},
{
0x108000,
0x108000,
0x4358,
0x4358,
SEG_XIP | SEG_EXEC | SEG_READ | SEG_WRITE,
SEG_KSP
},
{
0x10d000,
0x10d000,
0x2200,
0x2200,
SEG_XIP | SEG_EXEC | SEG_READ | SEG_WRITE,
SEG_KSP
},
{
0x110000,
0x110000,
0x75920,
0x75920,
SEG_XIP | SEG_EXEC | SEG_READ | SEG_WRITE,
SEG_KSP
},
{
0x186000,
0x8000,
0x0,
0x1a000,
SEG_READ | SEG_WRITE,
SEG_KSP
},
{
0x186000,
0x186000,
0x1be4,
0x1be4,
SEG_XIP | SEG_EXEC | SEG_READ | SEG_WRITE,
SEG_KSP
},
{
0x188000,
0x188000,
0x50dc,
0x50dc,
SEG_XIP | SEG_EXEC | SEG_READ | SEG_WRITE,
SEG_KSP
},
{
0x18e000,
0x22000,
0x0,
0x10,
SEG_READ | SEG_WRITE,
SEG_KSP
},
{
0x18e000,
0x18e000,
0x6654,
0x6654,
SEG_XIP | SEG_EXEC | SEG_READ | SEG_WRITE,
SEG_KSP
},
{
0x195000,
0x195000,
0x22c4,
0x22c4,
SEG_XIP | SEG_EXEC | SEG_READ | SEG_WRITE,
SEG_KSP
},
{
0x198000,
0x23000,
0x0,
0xc04,
SEG_READ | SEG_WRITE,
SEG_KSP
},
{
0x198000,
0x198000,
0x170c8,
0x170c8,
SEG_XIP | SEG_EXEC | SEG_READ | SEG_WRITE,
SEG_KSP
},
{
0x1b0000,
0x1b0000,
0x2c10,
0x2c10,
SEG_XIP | SEG_EXEC | SEG_READ | SEG_WRITE,
SEG_KSP
},
{
0,
0,
0,
0,
0,
0
},
{
0,
0,
0,
0,
0,
0
}
};
PhChunk __mkimage__label__ramChunks[64] = {
{ 0x0, 0x4000, PH_RAM_NONEXISTENT },
{ 0x4000, 0x20000, PH_RAM_ALLOCATED },
{ 0x24000, 0xdc000, PH_RAM_NONEXISTENT },
{ 0x100000, 0xb3000, PH_RAM_ALLOCATED },
{ 0x1b3000, 0xffe4d000, PH_RAM_NONEXISTENT }
};
EnvDesc __mkimage__label__environ = { 0x0, 0x0, (char*) 0x100000};
int heapSize = 0x2000;
char heap[0x2000];
BootConf __mkimage__label__bootConf = {
0x38216b39,
0,
{
5,
__mkimage__label__kernelSpace
},
0x0,
1,
__mkimage__label__banks,
11,
__mkimage__label__binDesc,
14,
__mkimage__label__segDesc,
{
64,
5,
__mkimage__label__ramChunks
},
0,
&__mkimage__label__environ,
heap,
heap,
heap + 8192,
};
BootConf* bootConf= &__mkimage__label__bootConf;
The kernelSpace field of the BootConf structure contains the description of the kernel address space that must be established by the microkernel's memory management module.
The descriptor specifies that the first 16M of the physical address space, which corresponds to RAM potentially available on the board, must be mapped to the first 16M of the virtual address space using one Block Address Translation register pairs (IBAT and DBAT). The space must be mapped read/write enforcing memory coherency (that is, the memory control bit M must be set in the BATs).
Another pair of BATs must be used to map to the virtual address range from 0x0f000000 to 0x0f020000. These are the PPC8260 internal memory mapped registers which occupy the physical addresses from 0xf000000 to 0x0f020000. The space must be mapped read-only, bypassing the memory cache.
The system image is stored in one memory bank that must be installed at the address 0x00100000. The size of the bank is 0x00b3000 bytes.
A third pair of BATs must be used to map the last 64M of the physical address space, which corresponds to ROM (FLASH) potentially available on the board. This space must be mapped read-only.
The system image contains 11 binaries:
-
dbgAgent and dbgBsp are the system level debug agent and its BSP
-
boot is the bootstrap program
-
reboot is the reboot program
-
kern is the microkernel
-
D_* are the driver binaries
-
PD is the per-actor/thread data manager system actor
-
kernonly_symb is the KDB symbol table
-
kernonly_bconf is the bootconf binary
Some binaries (for example, boot) have just one XIP segment which includes all text and data. Others (for instance, kern) have zero-initialized data (bss), link-edited in a separate segment.
The RAM allocator specifies that the RAM from address 0x00004000 to address 0x00024000 and from address 0x00100000 to address 0x001b3000 is allocated. The memory from 0x00100000 to 0x001b3000 is occupied by the system image memory bank, and the memory from 0x00004000 to 0x00024000 by the system control blocks and bss.
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