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Linux启动协议Ver.2.04

HuYi — Tue, 20 Jun 2006 06:46:00 GMT

THE LINUX/I386 BOOT PROTOCOL
----------------------------

H. Peter Anvin <hpa@zytor.com>
Last update 2005-09-02

On the i386 platform, the Linux kernel uses a rather complicated boot
convention. This has evolved partially due to historical aspects, as
well as the desire in the early days to have the kernel itself be a
bootable image, the complicated PC memory model and due to changed
expectations in the PC industry caused by the effective demise of
real-mode DOS as a mainstream operating system.

Currently, four versions of the Linux/i386 boot protocol exist.

Old kernels: zImage/Image support only. Some very early kernels
may not even support a command line.

Protocol 2.00: (Kernel 1.3.73) Added bzImage and initrd support, as
  well as a formalized way to communicate between the
  boot loader and the kernel. setup.S made relocatable,
  although the traditional setup area still assumed
  writable.

Protocol 2.01: (Kernel 1.3.76) Added a heap overrun warning.

Protocol 2.02: (Kernel 2.4.0-test3-pre3) New command line protocol.
  Lower the conventional memory ceiling. No overwrite
  of the traditional setup area, thus making booting
  safe for systems which use the EBDA from SMM or 32-bit
  BIOS entry points. zImage deprecated but still
  supported.

Protocol 2.03: (Kernel 2.4.18-pre1) Explicitly makes the highest possible
initrd address available to the bootloader.

Protocol 2.04: (Kernel 2.6.14) Extend the syssize field to four bytes.

**** MEMORY LAYOUT

The traditional memory map for the kernel loader, used for Image or
zImage kernels, typically looks like:

When using bzImage, the protected-mode kernel was relocated to
0x100000 ("high memory"), and the kernel real-mode block (boot sector,
setup, and stack/heap) was made relocatable to any address between
0x10000 and end of low memory. Unfortunately, in protocols 2.00 and
2.01 the command line is still required to live in the 0x9XXXX memory
range, and that memory range is still overwritten by the early kernel.
The 2.02 protocol resolves that problem.

It is desirable to keep the "memory ceiling" -- the highest point in
low memory touched by the boot loader -- as low as possible, since
some newer BIOSes have begun to allocate some rather large amounts of
memory, called the Extended BIOS Data Area, near the top of low
memory. The boot loader should use the "INT 12h" BIOS call to verify
how much low memory is available.

Unfortunately, if INT 12h reports that the amount of memory is too
low, there is usually nothing the boot loader can do but to report an
error to the user. The boot loader should therefore be designed to
take up as little space in low memory as it reasonably can. For
zImage or old bzImage kernels, which need data written into the
0x90000 segment, the boot loader should make sure not to use memory
above the 0x9A000 point; too many BIOSes will break above that point.

**** THE REAL-MODE KERNEL HEADER

In the following text, and anywhere in the kernel boot sequence, "a
sector" refers to 512 bytes. It is independent of the actual sector
size of the underlying medium.

The first step in loading a Linux kernel should be to load the
real-mode code (boot sector and setup code) and then examine the
following header at offset 0x01f1. The real-mode code can total up to
32K, although the boot loader may choose to load only the first two
sectors (1K) and then examine the bootup sector size.

The header looks like:

Offset Proto Name Meaning
/Size

01F1/1 ALL(1 setup_sects The size of the setup in sectors
01F2/2 ALL root_flags I(y��ng)f set, the root is mounted readonly
01F4/4 2.04+(2 syssize  The size of the 32-bit code in 16-byte paras
01F8/2 ALL ram_size DO NOT USE - for bootsect.S use only
01FA/2 ALL vid_mode Video mode control
01FC/2 ALL root_dev Default root device number
01FE/2 ALL boot_flag 0xAA55 magic number
0200/2 2.00+ jump  Jump instruction
0202/4 2.00+ header  Magic signature "HdrS"
0206/2 2.00+ version  Boot protocol version supported
0208/4 2.00+ realmode_swtch Boot loader hook (see below)
020C/2 2.00+ start_sys The load-low segment (0x1000) (obsolete)
020E/2 2.00+ kernel_version Pointer to kernel version string
0210/1 2.00+ type_of_loader Boot loader identifier
0211/1 2.00+ loadflags Boot protocol option flags
0212/2 2.00+ setup_move_size Move to high memory size (used with hooks)
0214/4 2.00+ code32_start Boot loader hook (see below)
0218/4 2.00+ ramdisk_image initrd load address (set by boot loader)
021C/4 2.00+ ramdisk_size initrd size (set by boot loader)
0220/4 2.00+ bootsect_kludge DO NOT USE - for bootsect.S use only
0224/2 2.01+ heap_end_ptr Free memory after setup end
0226/2 N/A pad1  Unused
0228/4 2.02+ cmd_line_ptr 32-bit pointer to the kernel command line
022C/4 2.03+ initrd_addr_max Highest legal initrd address

(1) For backwards compatibility, if the setup_sects field contains 0, the
real value is 4.

(2) For boot protocol prior to 2.04, the upper two bytes of the syssize
field are unusable, which means the size of a bzImage kernel
cannot be determined.

If the "HdrS" (0x53726448) magic number is not found at offset 0x202,
the boot protocol version is "old". Loading an old kernel, the
following parameters should be assumed:

I(y��ng)mage type = zImage
initrd not supported
Real-mode kernel must be located at 0x90000.

Otherwise, the "version" field contains the protocol version,
e.g. protocol version 2.01 will contain 0x0201 in this field. When
setting fields in the header, you must make sure only to set fields
supported by the protocol version in use.

The "kernel_version" field, if set to a nonzero value, contains a
pointer to a null-terminated human-readable kernel version number
string, less 0x200. This can be used to display the kernel version to
the user. This value should be less than (0x200*setup_sects). For
example, if this value is set to 0x1c00, the kernel version number
string can be found at offset 0x1e00 in the kernel file. This is a
valid value if and only if the "setup_sects" field contains the value
14 or higher.

Most boot loaders will simply load the kernel at its target address
directly. Such boot loaders do not need to worry about filling in
most of the fields in the header. The following fields should be
filled out, however:

vid_mode:
Please see the section on SPECIAL COMMAND LINE OPTIONS.

type_of_loader:
I(y��ng)f your boot loader has an assigned id (see table below), enter
0xTV here, where T is an identifier for the boot loader and V is
a version number. Otherwise, enter 0xFF here.

Assigned boot loader ids:
0 LILO
1 Loadlin
2 bootsect-loader
3 SYSLINUX
4 EtherBoot
5 ELILO
7 GRuB
8 U-BOOT

Please contact <hpa@zytor.com> if you need a bootloader ID
value assigned.

loadflags, heap_end_ptr:
I(y��ng)f the protocol version is 2.01 or higher, enter the
offset limit of the setup heap into heap_end_ptr and set the
0x80 bit (CAN_USE_HEAP) of loadflags. heap_end_ptr appears to
be relative to the start of setup (offset 0x0200).

setup_move_size:
When using protocol 2.00 or 2.01, if the real mode
kernel is not loaded at 0x90000, it gets moved there later in
the loading sequence. Fill in this field if you want
additional data (such as the kernel command line) moved in
addition to the real-mode kernel itself.

ramdisk_image, ramdisk_size:
I(y��ng)f your boot loader has loaded an initial ramdisk (initrd),
set ramdisk_image to the 32-bit pointer to the ramdisk data
and the ramdisk_size to the size of the ramdisk data.

The initrd should typically be located as high in memory as
possible, as it may otherwise get overwritten by the early
kernel initialization sequence. However, it must never be
located above the address specified in the initrd_addr_max
field. The initrd should be at least 4K page aligned.

cmd_line_ptr:
I(y��ng)f the protocol version is 2.02 or higher, this is a 32-bit
pointer to the kernel command line. The kernel command line
can be located anywhere between the end of setup and 0xA0000.
Fill in this field even if your boot loader does not support a
command line, in which case you can point this to an empty
string (or better yet, to the string "auto".) If this field
is left at zero, the kernel will assume that your boot loader
does not support the 2.02+ protocol.

ramdisk_max:
The maximum address that may be occupied by the initrd
contents. For boot protocols 2.02 or earlier, this field is
not present, and the maximum address is 0x37FFFFFF. (This
address is defined as the address of the highest safe byte, so
if your ramdisk is exactly 131072 bytes long and this field is
0x37FFFFFF, you can start your ramdisk at 0x37FE0000.)

**** THE KERNEL COMMAND LINE

The kernel command line has become an important way for the boot
loader to communicate with the kernel. Some of its options are also
relevant to the boot loader itself, see "special command line options"
below.

The kernel command line is a null-terminated string currently up to
255 characters long, plus the final null. A string that is too long
will be automatically truncated by the kernel, a boot loader may allow
a longer command line to be passed to permit future kernels to extend
this limit.

If the boot protocol version is 2.02 or later, the address of the
kernel command line is given by the header field cmd_line_ptr (see
above.) This address can be anywhere between the end of the setup
heap and 0xA0000.

If the protocol version is *not* 2.02 or higher, the kernel
command line is entered using the following protocol:

At offset 0x0020 (word), "cmd_line_magic", enter the magic
number 0xA33F.

At offset 0x0022 (word), "cmd_line_offset", enter the offset
of the kernel command line (relative to the start of the
real-mode kernel).

The kernel command line *must* be within the memory region
covered by setup_move_size, so you may need to adjust this
field.

**** SAMPLE BOOT CONFIGURATION

As a sample configuration, assume the following layout of the real
mode segment (this is a typical, and recommended layout):

0x0000-0x7FFF Real mode kernel
0x8000-0x8FFF Stack and heap
0x9000-0x90FF Kernel command line

Such a boot loader should enter the following fields in the header:

unsigned long base_ptr; /* base address for real-mode segment */

if ( setup_sects == 0 ) {
setup_sects = 4;
}

if ( protocol >= 0x0200 ) {
  type_of_loader = ;
  if ( loading_initrd ) {
   ramdisk_image = ;
   ramdisk_size = ;
  }
  if ( protocol >= 0x0201 ) {
   heap_end_ptr = 0x9000 - 0x200;
   loadflags |= 0x80; /* CAN_USE_HEAP */
  }
  if ( protocol >= 0x0202 ) {
   cmd_line_ptr = base_ptr + 0x9000;
  } else {
   cmd_line_magic = 0xA33F;
   cmd_line_offset = 0x9000;
   setup_move_size = 0x9100;
  }
} else {
  /* Very old kernel */

cmd_line_magic = 0xA33F;
cmd_line_offset = 0x9000;

/* A very old kernel MUST have its real-mode code
loaded at 0x90000 */

  if ( base_ptr != 0x90000 ) {
   /* Copy the real-mode kernel */
   memcpy(0x90000, base_ptr, (setup_sects+1)*512);
   /* Copy the command line */
   memcpy(0x99000, base_ptr+0x9000, 256);

base_ptr = 0x90000; /* Relocated */
}

  /* It is recommended to clear memory up to the 32K mark */
  memset(0x90000 + (setup_sects+1)*512, 0,
         (64-(setup_sects+1))*512);
}

**** LOADING THE REST OF THE KERNEL

The 32-bit (non-real-mode) kernel starts at offset (setup_sects+1)*512
in the kernel file (again, if setup_sects == 0 the real value is 4.)
It should be loaded at address 0x10000 for Image/zImage kernels and
0x100000 for bzImage kernels.

The kernel is a bzImage kernel if the protocol >= 2.00 and the 0x01
bit (LOAD_HIGH) in the loadflags field is set:

is_bzImage = (protocol >= 0x0200) && (loadflags & 0x01);
load_address = is_bzImage ? 0x100000 : 0x10000;

Note that Image/zImage kernels can be up to 512K in size, and thus use
the entire 0x10000-0x90000 range of memory. This means it is pretty
much a requirement for these kernels to load the real-mode part at
0x90000. bzImage kernels allow much more flexibility.

**** SPECIAL COMMAND LINE OPTIONS

If the command line provided by the boot loader is entered by the
user, the user may expect the following command line options to work.
They should normally not be deleted from the kernel command line even
though not all of them are actually meaningful to the kernel. Boot
loader authors who need additional command line options for the boot
loader itself should get them registered in
Documentation/kernel-parameters.txt to make sure they will not
conflict with actual kernel options now or in the future.

vga=
here is either an integer (in C notation, either
decimal, octal, or hexadecimal) or one of the strings
"normal" (meaning 0xFFFF), "ext" (meaning 0xFFFE) or "ask"
(meaning 0xFFFD). This value should be entered into the
vid_mode field, as it is used by the kernel before the command
line is parsed.

mem=
is an integer in C notation optionally followed by K, M
or G (meaning << 10, << 20 or << 30). This specifies the end
of memory to the kernel. This affects the possible placement
of an initrd, since an initrd should be placed near end of
memory. Note that this is an option to *both* the kernel and
the bootloader!

initrd=
An initrd should be loaded. The meaning of is
obviously bootloader-dependent, and some boot loaders
(e.g. LILO) do not have such a command.

In addition, some boot loaders add the following options to the
user-specified command line:

BOOT_IMAGE=
The boot image which was loaded. Again, the meaning of
is obviously bootloader-dependent.

auto
The kernel was booted without explicit user intervention.

If these options are added by the boot loader, it is highly
recommended that they are located *first*, before the user-specified
or configuration-specified command line. Otherwise, "init=/bin/sh"
gets confused by the "auto" option.

**** RUNNING THE KERNEL

The kernel is started by jumping to the kernel entry point, which is
located at *segment* offset 0x20 from the start of the real mode
kernel. This means that if you loaded your real-mode kernel code at
0x90000, the kernel entry point is 9020:0000.

At entry, ds = es = ss should point to the start of the real-mode
kernel code (0x9000 if the code is loaded at 0x90000), sp should be
set up properly, normally pointing to the top of the heap, and
interrupts should be disabled. Furthermore, to guard against bugs in
the kernel, it is recommended that the boot loader sets fs = gs = ds =
es = ss.

In our example from above, we would do:

/* Note: in the case of the "old" kernel protocol, base_ptr must
be == 0x90000 at this point; see the previous sample code */

seg = base_ptr >> 4;

cli(); /* Enter with interrupts disabled! */

/* Set up the real-mode kernel stack */
_SS = seg;
_SP = 0x9000; /* Load SP immediately after loading SS! */

_DS = _ES = _FS = _GS = seg;
jmp_far(seg+0x20, 0); /* Run the kernel */

If your boot sector accesses a floppy drive, it is recommended to
switch off the floppy motor before running the kernel, since the
kernel boot leaves interrupts off and thus the motor will not be
switched off, especially if the loaded kernel has the floppy driver as
a demand-loaded module!

**** ADVANCED BOOT TIME HOOKS

If the boot loader runs in a particularly hostile environment (such as
LOADLIN, which runs under DOS) it may be impossible to follow the
standard memory location requirements. Such a boot loader may use the
following hooks that, if set, are invoked by the kernel at the
appropriate time. The use of these hooks should probably be
considered an absolutely last resort!

IMPORTANT: All the hooks are required to preserve %esp, %ebp, %esi and
%edi across invocation.

realmode_swtch:
A 16-bit real mode far subroutine invoked immediately before
entering protected mode. The default routine disables NMI, so
your routine should probably do so, too.

code32_start:
A 32-bit flat-mode routine *jumped* to immediately after the
transition to protected mode, but before the kernel is
uncompressed. No segments, except CS, are set up; you should
set them up to KERNEL_DS (0x18) yourself.

After completing your hook, you should jump to the address
that was in this field before your boot loader overwrote it.

HuYi 2006-06-20 14:46 发表评论

HuYi — Tue, 18 Apr 2006 03:20:00 GMT

HuYi 2006-04-18 11:20 发表评论

Linux下获取文件变更通知

HuYi — Thu, 13 Apr 2006 05:35:00 GMT

文章是在�|�上搜到的，我只是截取了(ji��n)其中一�D�c(di��n)�?br />

#define _GNU_SOURCE /* needed to get the defines */
#include /* in glibc 2.2 this has the needed
values defined */
#include
#include
#include

static volatile int event_fd;

// 信号处理例程
static void handler(int sig, siginfo_t *si, void *data)
{
event_fd = si->si_fd;
}

int main(void)
{
struct sigaction act;
int fd;

// 登记信号处理例程
act.sa_sigaction = handler;
sigemptyset(&act.sa_mask);
act.sa_flags = SA_SIGINFO;
sigaction(SIGRTMIN, &act, NULL);

// 需要了(ji��n)解当前目�?."的情况�?/span>
fd = open(".", O_RDONLY);
fcntl(fd, F_SETSIG, SIGRTMIN);
fcntl(fd, F_NOTIFY, DN_MODIFY|DN_CREATE|DN_MULTISHOT);
/* we will now be notified if any of the files
in "." is modified or new files are created */
while (1) {
// 收到信号后，��׃��(x��)执行信号处理例程。�?br />// 而 pause() 也就�l�束�?ji��n)。�?/span>
pause();
printf("Got event on fd=%d\n", event_fd);
}
}

上面�q�一��段例程�Q�对于熟�(zh��n)?Linux �pȝ��~�程的读者朋友们来说�Q�是很容易理解的。程序首先注册一个信号处理例�E�，然后通知 Kernel�Q�我要观�?fd 上的 DN_MODIFY �?DN_CREATE �?DN_MULTISHOT 事�g。（关于�q�些事�g的详�l�定义，误��者朋友们参阅文后所列的参考资料。）(j��) Linux Kernel 收到�q�个��h��后，把相应的 fd �?inode �l�做上记��P��然后 Linux Kernel 和用户应用程序就自顾自去处理各自的别的事情去�?ji��n)。等�?inode 上发生了(ji��n)相应的事�Ӟ��Linux Kernel ��把信号发给用户�q�程�Q�于是开始执行信号处理例�E�，用户�E�序�Ҏ(gu��)��件系�l�上的变化也��可以及(qi��ng)时的做出反应�?ji��n)。而在�q�整个过�E�中�Q�系�l�以�?qi��ng)用��L(f��ng)��序的正常�q�行基本上未受到性能上的影响。这里还需要说明的是，dnotify �q�没有通过增加新的�pȝ��调用来完成它的功能，而是通过 fcntl 来完成�Q务的。增加一个系�l�调用，相对来说是一个很大的手术�Q�而且如果设计不当�Q�处理得不好的话�Q�伤疤会(x��)一直留在那里，�q�是 Linux Kernel 的开发者们所非常不愿意见到的事情�?

HuYi 2006-04-13 13:35 发表评论

gun常用工具手册�?chm�?

HuYi — Wed, 12 Apr 2006 07:09:00 GMT

我把�l�常用到的GNU工具文档做成�?ji��n)chm文�g�Q�提供给需要的朋友下蝲�?br />包括如下手册�Q?br />    C library
    awk
    autogen
    automake
    bash
    tar
    gsasl
    sed

http://www.shnenglu.com/Files/huyi/gnu.part1.rar
http://www.shnenglu.com/Files/huyi/gnu.part2.rar

HuYi 2006-04-12 15:09 发表评论

GCC参数��解

HuYi — Mon, 20 Mar 2006 02:30:00 GMT

[介绍]
gcc and g++分别是gnu的c & c++�~�译�?gcc/g++在执行编译工作的时候，��d��需�?�?

1.预处�?生成.i的文件[预处理器cpp]
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3.有汇�~�变为目标代�?机器代码)生成.o的文件[汇编器as]
4.�q�接目标代码,生成可执行程序[链接器ld]
[参数详解]
-x language filename
　讑֮�文�g所使用的语�a�,使后�~�名无�?对以后的多个有效.也就是根据约定C语言的后
�~�名称�?c的，而C++的后�~�名是.C或�?cpp,如果你很个性，军_��你的C代码文�g的后�~�
名是.pig 哈哈�Q�那你就要用�q�个参数,�q�个参数对他后面的文件名都�v作用�Q�除非到�?
下一个参数的使用�?
　　可以使用的参数吗有下面的�q�些
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ssembler-with-cpp'.
　　看到英文�Q�应该可以理解的�?
　　例子用法:
　　gcc -x c hello.pig
　　
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-E
　　只激�z�预处理,�q�个不生成文�?你需要把它重定向��C��个输出文仉��?
　　例子用法:
　　gcc -E hello.c > pianoapan.txt
　　gcc -E hello.c | more
　　慢慢看吧,一个hello word 也要与处理成800行的代码
-o
　　制定目标名称,�~�省的时�?gcc �~�译出来的文件是a.out,很难�?如果你和我有同感
�Q�改掉它,哈哈
　　例子用法
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-pipe
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　　在你是用#include"file"的时�?gcc/g++�?x��)先在当前目录查找你所制定的头文�g,�?
果没有找�?他回到缺省的头文件目录找,如果使用-I制定�?ji��n)目�?�?
　　回先在你所制定的目录查�?然后再按常规的顺序去�?
　　对于#include,gcc/g++�?x��)�?I制定的目录查�?查找不到,然后��到�pȝ��的缺
省的头文件目录查�?
　　
-I-
　　��是取消前一个参数的功能,所以一般在-Idir之后使用
　　
-idirafter dir
　　�?I的目录里面查扑֤��?讲到�q�个目录里面查找.
　　
-iprefix prefix
-iwithprefix dir
　　一般一起��?�?I的目录查扑֤��?�?x��)到prefix+dir下查�?
　　
-nostdinc
　　使编译器不再�pȝ��~�省的头文�g目录里面扑֤�文�g,一般和-I联合使用,明确限定�?
文�g的位�|?
　　
-nostdin C++
　　规定不在g++指定的标准�\�l�中搜烦(ch��),但仍在其他�\径中搜烦(ch��),.此选项在创libg++�?
使用
　　
-C
　　在预处理的时�?不删除注释信�?一般和-E使用,有时候分析程序，用这个很方便�?

　　
-M
　　生成文�g兌��的信息。包含目标文件所依赖的所有源代码你可以用gcc -M hello.c
来测试一下，很简单�?
　　
-MM
　　和上面的那个一��P��但是它将忽略�?include造成的依赖关�p�R�?
　　
-MD
　　�?M相同�Q�但是输出将导入�?d的文仉��?
　　
-MMD
　　�?MM相同�Q�但是输出将导入�?d的文仉��?
　　
-Wa,option
　　此选项传递option�l�汇�~�程�?如果option中间有逗号,��将option分成多个选项,�?
后传递给�?x��)汇�~�程�?
　　
-Wl.option
　　此选项传递option�l�连接程�?如果option中间有逗号,��将option分成多个选项,�?
后传递给�?x��)连接程�?
　　
-llibrary
　　制定�~�译的时候��用的�?
　　例子用法
　　gcc -lcurses hello.c
　　使用ncurses库编译程�?
　　
-Ldir
　　制定�~�译的时候，搜烦(ch��)库的路径。比如你自己的库�Q�可以用它制定目录，不然
　　�~�译器将只在标准库的目录找。这个dir��是目录的名�U��?
　　
-O0
-O1
-O2
-O3
　　�~�译器的优化选项�?个��别，-O0表示没有优化,-O1为缺省��|��-O3优化�U�别最高　
　　　
-g
　　只是�~�译器，在编译的时候，产生调试信息�?
　　
-gstabs
　　此选项以stabs格式声称调试信息,但是不包括gdb调试信息.
　　
-gstabs+
　　此选项以stabs格式声称调试信息,�q�且包含仅供gdb使用的额外调试信�?
　　
-ggdb
　　此选项��尽可能的生成gdb的可以��用的调试信息.
-static
　　此选项��禁止��用动态库�Q�所以，�~�译出来的东西，一般都很大�Q�也不需要什�?
动态连接库�Q�就可以�q�行.
-share
　　此选项��尽量��用动态库�Q�所以生成文件比较小�Q�但是需要系�l�由动态库.
-traditional
　　试图让编译器支持传统的C语言�Ҏ(gu��)�?
[参考资料]
-Linux/UNIX高��~�程
　　中科�U�旗软�g技术有限公司编�?清华大学出版�C�և��?
-Gcc man page
　　
[ChangeLog]
-2002-08-10
　　ver 0.1 发布最初的文档
-2002-08-11
　　ver 0.11 修改文档格式
-2002-08-12
　　ver 0.12 加入�?ji��n)对静(r��n)态库�Q�动态库的参�?
-2002-08-16
　　ver 0.16 增加�?ji��n)gcc�~�译�?个阶�D늚�命��o(h��)
�q�行 gcc/egcs
**********�q�行 gcc/egcs***********************
　　GCC �?GNU �?C �?C++ �~�译器。实际上�Q�GCC 能够�~�译三种语言�Q�C、C++ �?O
bject C�Q�C 语言的一�U�面向对象扩展）(j��)。利�?gcc 命��o(h��)可同时编译�ƈ�q�接 C �?C++
源程序�?
　　如果你有两个或少数几�?C 源文�Ӟ��也可以方便地利用 GCC �~�译、连接�ƈ生成�?
执行文�g。例如，假设你有两个源文�?main.c �?factorial.c 两个源文�Ӟ��现在要编
译生成一个计��阶乘的�E�序�?
代码:
-----------------------
清单 factorial.c
-----------------------
int factorial (int n)
{
　　if (n <= 1)
　　　return 1;
　　else
　　　return factorial (n - 1) * n;
}
-----------------------
清单 main.c
-----------------------
#include　
#include　
int factorial (int n);
int main (int argc, char **argv)
{
　　int n;
　　if (argc < 2)
　　{
　　　　printf ("Usage: %s n\n", argv [0]);
　　　　return -1;
　　}
　　else
　　{
　　　n = atoi (argv[1]);
　　　printf ("Factorial of %d is %d.\n", n, factorial (n));
　　 }
　　return 0;
}
-----------------------
利用如下的命令可�~�译生成可执行文�Ӟ��q�执行程序：(x��)
$ gcc -o factorial main.c factorial.c
$ ./factorial 5
Factorial of 5 is 120.
　　GCC 可同时用来编�?C �E�序�?C++ �E�序。一般来��_(d��)��C �~�译器通过源文件的后缀
名来判断�?C �E�序�q�是 C++ �E�序。在 Linux 中，C 源文件的后缀名�ؓ(f��) .c�Q��?C++ �?
文�g的后�~�名�ؓ(f��) .C �?.cpp。但是，gcc 命��o(h��)只能�~�译 C++ 源文�Ӟ��而不能自动和 C
++ �E�序使用的库�q�接。因此，通常使用 g++ 命��o(h��)来完�?C++ �E�序的编译和�q�接�Q�该�E?
序会(x��)自动调用 gcc 实现�~�译。假设我们有一个如下的 C++ 源文�Ӟ��hello.C�Q�：(x��)
#include
void main (void)
{
　　cout << "Hello, world!" << endl;
}
则可以如下调�?g++ 命��o(h��)�~�译、连接�ƈ生成可执行文�Ӟ��(x��)
$ g++ -o hello hello.C
$ ./hello
Hello, world!
**********************gcc/egcs 的主要选项*********
gcc 命��o(h��)的常用选项
选项解释
-ansi 只支�?ANSI 标准�?C 语法。这一选项��禁�?GNU C 的某些特�Ԍ��
例如 asm �?typeof 关键词�?
-c 只编译�ƈ生成目标文�g�?
-DMACRO 以字�W�串�?”定�?MACRO 宏�?
-DMACRO=DEFN 以字�W�串“DEFN”定�?MACRO 宏�?
-E 只运�?C 预编译器�?
-g 生成调试信息。GNU 调试器可利用该信息�?
-IDIRECTORY 指定额外的头文�g搜烦(ch��)路径DIRECTORY�?
-LDIRECTORY 指定额外的函数库搜烦(ch��)路径DIRECTORY�?
-lLIBRARY �q�接时搜索指定的函数库LIBRARY�?
-m486 针对 486 �q�行代码优化�?
-o FILE 生成指定的输出文件。用在生成可执行文�g时�?
-O0 不进行优化处理�?
-O �?-O1 优化生成代码�?
-O2 �q�一步优化�?
-O3 �?-O2 更进一步优化，包括 inline 函数�?
-shared 生成�׃�n目标文�g。通常用在建立�׃�n库时�?
-static ��止使用�׃�n�q�接�?
-UMACRO 取消�?MACRO 宏的定义�?
-w 不生成�Q何警告信息�?
-Wall 生成所有警告信息�?img src ="http://www.shnenglu.com/huyi/aggbug/4354.html" width = "1" height = "1" />

HuYi 2006-03-20 10:30 发表评论

C++对�ƈ行运��的支持

HuYi — Mon, 13 Mar 2006 07:22:00 GMT

MPICH�Q�支持大规模�Q�复杂的集群�~�程�Q�强力支持SPMD模型�Q�也支持SMP�Q�MPP和多用户配置�?BR>PVM�Q?nbsp; 支持异构环境集群�~�程�Q�很�Ҏ(gu��)��用于单用��P��中小规模的集��应用程序，支持MPP�?BR>MICO�Q?nbsp; 支持分布式和面向对象的�ƈ行编�E�，包括对agent和多agent�~�程的良好支持�?BR>POSIX�Q?支持函数或对象��单个应用�E�序内的�q�行处理�Q�可以用来利用SMP�Q�MPP的优�ѝ�?/P>

HuYi 2006-03-13 15:22 发表评论

HuYi — Thu, 09 Mar 2006 08:02:00 GMT

信号量：(x��)
��单点��_(d��)��是
1 一个整数变量i�?BR> 2 一个等待进�E�链表�?BR> 3 一对P/V操作函数�?BR>P��i�?�Q�如果i<0�?ji��n)，��把当前正在�q�行的进�E�加入到�q�程链表中，�q��塞之�?BR>V��i�?�Q�如果i>=0,则激�z�链表中�?个或者多个进�E��?BR>同时适用于单处理器和多处理器

自旋锁：(x��)
在多处理器中�Q�如果修改一些内核结构所需要的旉��非常短（短于把进�E�插入进�E�链表中�q�挂起它所需要的旉��Q�，则应该��用自旋锁�?/P>

HuYi 2006-03-09 16:02 发表评论

[��知识]存储器管理区

HuYi — Tue, 07 Mar 2006 09:11:00 GMT

80x86体系�l�构的两�U�硬件约束：(x��)
1。ISA�ȝ��直接存储器存取（DMA�Q�只能对RAM的前16MB��d��?BR>2。在大RAM�?2位机中，�׃��U�性地址�I�间太小的原因，CPU不能直接讉K��所有物理存储器�?BR>
所以，Linux把物理存储器分�ؓ(f��)三个��理区：(x��)
ZONE_DMA <= 16MB
16MB < ZONE_NORMAL < 896MB
ZONE_HIGHMEM > 896MB

�?4位机中没有��用ZONE_HIGHNEN

HuYi 2006-03-07 17:11 发表评论