forked from Minki/linux
mainlining shenanigans
b4fc1a460f
Alexei Starovoitov says: ==================== eBPF syscall, verifier, testsuite v14 -> v15: - got rid of macros with hidden control flow (suggested by David) replaced macro with explicit goto or return and simplified where possible (affected patches #9 and #10) - rebased, retested v13 -> v14: - small change to 1st patch to ease 'new userspace with old kernel' problem (done similar to perf_copy_attr()) (suggested by Daniel) - the rest unchanged v12 -> v13: - replaced 'foo __user *' pointers with __aligned_u64 (suggested by David) - added __attribute__((aligned(8)) to 'union bpf_attr' to keep constant alignment between patches - updated manpage and syscall wrappers due to __aligned_u64 - rebased, retested on x64 with 32-bit and 64-bit userspace and on i386, build tested on arm32,sparc64 v11 -> v12: - dropped patch 11 and copied few macros to libbpf.h (suggested by Daniel) - replaced 'enum bpf_prog_type' with u32 to be safe in compat (.. Andy) - implemented and tested compat support (not part of this set) (.. Daniel) - changed 'void *log_buf' to 'char *' (.. Daniel) - combined struct bpf_work_struct and bpf_prog_info (.. Daniel) - added better return value explanation to manpage (.. Andy) - added log_buf/log_size explanation to manpage (.. Andy & Daniel) - added a lot more info about prog_type and map_type to manpage (.. Andy) - rebased, tweaked test_stubs Patches 1-4 establish BPF syscall shell for maps and programs. Patches 5-10 add verifier step by step Patch 11 adds test stubs for 'unspec' program type and verifier testsuite from user space Note that patches 1,3,4,7 add commands and attributes to the syscall while being backwards compatible from each other, which should demonstrate how other commands can be added in the future. After this set the programs can be loaded for testing only. They cannot be attached to any events. Though manpage talks about tracing and sockets, it will be a subject of future patches. Please take a look at manpage: BPF(2) Linux Programmer's Manual BPF(2) NAME bpf - perform a command on eBPF map or program SYNOPSIS #include <linux/bpf.h> int bpf(int cmd, union bpf_attr *attr, unsigned int size); DESCRIPTION bpf() syscall is a multiplexor for a range of different operations on eBPF which can be characterized as "universal in-kernel virtual machine". eBPF is similar to original Berkeley Packet Filter (or "classic BPF") used to filter network packets. Both statically analyze the programs before loading them into the kernel to ensure that programs cannot harm the running system. eBPF extends classic BPF in multiple ways including ability to call in- kernel helper functions and access shared data structures like eBPF maps. The programs can be written in a restricted C that is compiled into eBPF bytecode and executed on the eBPF virtual machine or JITed into native instruction set. eBPF Design/Architecture eBPF maps is a generic storage of different types. User process can create multiple maps (with key/value being opaque bytes of data) and access them via file descriptor. In parallel eBPF programs can access maps from inside the kernel. It's up to user process and eBPF program to decide what they store inside maps. eBPF programs are similar to kernel modules. They are loaded by the user process and automatically unloaded when process exits. Each eBPF program is a safe run-to-completion set of instructions. eBPF verifier statically determines that the program terminates and is safe to execute. During verification the program takes a hold of maps that it intends to use, so selected maps cannot be removed until the program is unloaded. The program can be attached to different events. These events can be packets, tracepoint events and other types in the future. A new event triggers execution of the program which may store information about the event in the maps. Beyond storing data the programs may call into in-kernel helper functions which may, for example, dump stack, do trace_printk or other forms of live kernel debugging. The same program can be attached to multiple events. Different programs can access the same map: tracepoint tracepoint tracepoint sk_buff sk_buff event A event B event C on eth0 on eth1 | | | | | | | | | | --> tracing <-- tracing socket socket prog_1 prog_2 prog_3 prog_4 | | | | |--- -----| |-------| map_3 map_1 map_2 Syscall Arguments bpf() syscall operation is determined by cmd which can be one of the following: BPF_MAP_CREATE Create a map with given type and attributes and return map FD BPF_MAP_LOOKUP_ELEM Lookup element by key in a given map and return its value BPF_MAP_UPDATE_ELEM Create or update element (key/value pair) in a given map BPF_MAP_DELETE_ELEM Lookup and delete element by key in a given map BPF_MAP_GET_NEXT_KEY Lookup element by key in a given map and return key of next element BPF_PROG_LOAD Verify and load eBPF program attr is a pointer to a union of type bpf_attr as defined below. size is the size of the union. union bpf_attr { struct { /* anonymous struct used by BPF_MAP_CREATE command */ __u32 map_type; __u32 key_size; /* size of key in bytes */ __u32 value_size; /* size of value in bytes */ __u32 max_entries; /* max number of entries in a map */ }; struct { /* anonymous struct used by BPF_MAP_*_ELEM commands */ __u32 map_fd; __aligned_u64 key; union { __aligned_u64 value; __aligned_u64 next_key; }; }; struct { /* anonymous struct used by BPF_PROG_LOAD command */ __u32 prog_type; __u32 insn_cnt; __aligned_u64 insns; /* 'const struct bpf_insn *' */ __aligned_u64 license; /* 'const char *' */ __u32 log_level; /* verbosity level of eBPF verifier */ __u32 log_size; /* size of user buffer */ __aligned_u64 log_buf; /* user supplied 'char *' buffer */ }; } __attribute__((aligned(8))); eBPF maps maps is a generic storage of different types for sharing data between kernel and userspace. Any map type has the following attributes: . type . max number of elements . key size in bytes . value size in bytes The following wrapper functions demonstrate how this syscall can be used to access the maps. The functions use the cmd argument to invoke different operations. BPF_MAP_CREATE int bpf_create_map(enum bpf_map_type map_type, int key_size, int value_size, int max_entries) { union bpf_attr attr = { .map_type = map_type, .key_size = key_size, .value_size = value_size, .max_entries = max_entries }; return bpf(BPF_MAP_CREATE, &attr, sizeof(attr)); } bpf() syscall creates a map of map_type type and given attributes key_size, value_size, max_entries. On success it returns process-local file descriptor. On error, -1 is returned and errno is set to EINVAL or EPERM or ENOMEM. The attributes key_size and value_size will be used by verifier during program loading to check that program is calling bpf_map_*_elem() helper functions with correctly initialized key and that program doesn't access map element value beyond specified value_size. For example, when map is created with key_size = 8 and program does: bpf_map_lookup_elem(map_fd, fp - 4) such program will be rejected, since in-kernel helper function bpf_map_lookup_elem(map_fd, void *key) expects to read 8 bytes from 'key' pointer, but 'fp - 4' starting address will cause out of bounds stack access. Similarly, when map is created with value_size = 1 and program does: value = bpf_map_lookup_elem(...); *(u32 *)value = 1; such program will be rejected, since it accesses value pointer beyond specified 1 byte value_size limit. Currently only hash table map_type is supported: enum bpf_map_type { BPF_MAP_TYPE_UNSPEC, BPF_MAP_TYPE_HASH, }; map_type selects one of the available map implementations in kernel. For all map_types eBPF programs access maps with the same bpf_map_lookup_elem()/bpf_map_update_elem() helper functions. BPF_MAP_LOOKUP_ELEM int bpf_lookup_elem(int fd, void *key, void *value) { union bpf_attr attr = { .map_fd = fd, .key = ptr_to_u64(key), .value = ptr_to_u64(value), }; return bpf(BPF_MAP_LOOKUP_ELEM, &attr, sizeof(attr)); } bpf() syscall looks up an element with given key in a map fd. If element is found it returns zero and stores element's value into value. If element is not found it returns -1 and sets errno to ENOENT. BPF_MAP_UPDATE_ELEM int bpf_update_elem(int fd, void *key, void *value) { union bpf_attr attr = { .map_fd = fd, .key = ptr_to_u64(key), .value = ptr_to_u64(value), }; return bpf(BPF_MAP_UPDATE_ELEM, &attr, sizeof(attr)); } The call creates or updates element with given key/value in a map fd. On success it returns zero. On error, -1 is returned and errno is set to EINVAL or EPERM or ENOMEM or E2BIG. E2BIG indicates that number of elements in the map reached max_entries limit specified at map creation time. BPF_MAP_DELETE_ELEM int bpf_delete_elem(int fd, void *key) { union bpf_attr attr = { .map_fd = fd, .key = ptr_to_u64(key), }; return bpf(BPF_MAP_DELETE_ELEM, &attr, sizeof(attr)); } The call deletes an element in a map fd with given key. Returns zero on success. If element is not found it returns -1 and sets errno to ENOENT. BPF_MAP_GET_NEXT_KEY int bpf_get_next_key(int fd, void *key, void *next_key) { union bpf_attr attr = { .map_fd = fd, .key = ptr_to_u64(key), .next_key = ptr_to_u64(next_key), }; return bpf(BPF_MAP_GET_NEXT_KEY, &attr, sizeof(attr)); } The call looks up an element by key in a given map fd and returns key of the next element into next_key pointer. If key is not found, it return zero and returns key of the first element into next_key. If key is the last element, it returns -1 and sets errno to ENOENT. Other possible errno values are ENOMEM, EFAULT, EPERM, EINVAL. This method can be used to iterate over all elements of the map. close(map_fd) will delete the map map_fd. Exiting process will delete all maps automatically. eBPF programs BPF_PROG_LOAD This cmd is used to load eBPF program into the kernel. char bpf_log_buf[LOG_BUF_SIZE]; int bpf_prog_load(enum bpf_prog_type prog_type, const struct bpf_insn *insns, int insn_cnt, const char *license) { union bpf_attr attr = { .prog_type = prog_type, .insns = ptr_to_u64(insns), .insn_cnt = insn_cnt, .license = ptr_to_u64(license), .log_buf = ptr_to_u64(bpf_log_buf), .log_size = LOG_BUF_SIZE, .log_level = 1, }; return bpf(BPF_PROG_LOAD, &attr, sizeof(attr)); } prog_type is one of the available program types: enum bpf_prog_type { BPF_PROG_TYPE_UNSPEC, BPF_PROG_TYPE_SOCKET, BPF_PROG_TYPE_TRACING, }; By picking prog_type program author selects a set of helper functions callable from eBPF program and corresponding format of struct bpf_context (which is the data blob passed into the program as the first argument). For example, the programs loaded with prog_type = TYPE_TRACING may call bpf_printk() helper, whereas TYPE_SOCKET programs may not. The set of functions available to the programs under given type may increase in the future. Currently the set of functions for TYPE_TRACING is: bpf_map_lookup_elem(map_fd, void *key) // lookup key in a map_fd bpf_map_update_elem(map_fd, void *key, void *value) // update key/value bpf_map_delete_elem(map_fd, void *key) // delete key in a map_fd bpf_ktime_get_ns(void) // returns current ktime bpf_printk(char *fmt, int fmt_size, ...) // prints into trace buffer bpf_memcmp(void *ptr1, void *ptr2, int size) // non-faulting memcmp bpf_fetch_ptr(void *ptr) // non-faulting load pointer from any address bpf_fetch_u8(void *ptr) // non-faulting 1 byte load bpf_fetch_u16(void *ptr) // other non-faulting loads bpf_fetch_u32(void *ptr) bpf_fetch_u64(void *ptr) and bpf_context is defined as: struct bpf_context { /* argN fields match one to one to arguments passed to trace events */ u64 arg1, arg2, arg3, arg4, arg5, arg6; /* return value from kretprobe event or from syscall_exit event */ u64 ret; }; The set of helper functions for TYPE_SOCKET is TBD. More program types may be added in the future. Like BPF_PROG_TYPE_USER_TRACING for unprivileged programs. BPF_PROG_TYPE_UNSPEC is used for testing only. Such programs cannot be attached to events. insns array of "struct bpf_insn" instructions insn_cnt number of instructions in the program license license string, which must be GPL compatible to call helper functions marked gpl_only log_buf user supplied buffer that in-kernel verifier is using to store verification log. Log is a multi-line string that should be used by program author to understand how verifier came to conclusion that program is unsafe. The format of the output can change at any time as verifier evolves. log_size size of user buffer. If size of the buffer is not large enough to store all verifier messages, -1 is returned and errno is set to ENOSPC. log_level verbosity level of eBPF verifier, where zero means no logs provided close(prog_fd) will unload eBPF program The maps are accesible from programs and generally tie the two together. Programs process various events (like tracepoint, kprobe, packets) and store the data into maps. User space fetches data from maps. Either the same or a different map may be used by user space as configuration space to alter program behavior on the fly. Events Once an eBPF program is loaded, it can be attached to an event. Various kernel subsystems have different ways to do so. For example: setsockopt(sock, SOL_SOCKET, SO_ATTACH_BPF, &prog_fd, sizeof(prog_fd)); will attach the program prog_fd to socket sock which was received by prior call to socket(). ioctl(event_fd, PERF_EVENT_IOC_SET_BPF, prog_fd); will attach the program prog_fd to perf event event_fd which was received by prior call to perf_event_open(). Another way to attach the program to a tracing event is: event_fd = open("/sys/kernel/debug/tracing/events/skb/kfree_skb/filter"); write(event_fd, "bpf-123"); /* where 123 is eBPF program FD */ /* here program is attached and will be triggered by events */ close(event_fd); /* to detach from event */ EXAMPLES /* eBPF+sockets example: * 1. create map with maximum of 2 elements * 2. set map[6] = 0 and map[17] = 0 * 3. load eBPF program that counts number of TCP and UDP packets received * via map[skb->ip->proto]++ * 4. attach prog_fd to raw socket via setsockopt() * 5. print number of received TCP/UDP packets every second */ int main(int ac, char **av) { int sock, map_fd, prog_fd, key; long long value = 0, tcp_cnt, udp_cnt; map_fd = bpf_create_map(BPF_MAP_TYPE_HASH, sizeof(key), sizeof(value), 2); if (map_fd < 0) { printf("failed to create map '%s'\n", strerror(errno)); /* likely not run as root */ return 1; } key = 6; /* ip->proto == tcp */ assert(bpf_update_elem(map_fd, &key, &value) == 0); key = 17; /* ip->proto == udp */ assert(bpf_update_elem(map_fd, &key, &value) == 0); struct bpf_insn prog[] = { BPF_MOV64_REG(BPF_REG_6, BPF_REG_1), /* r6 = r1 */ BPF_LD_ABS(BPF_B, 14 + 9), /* r0 = ip->proto */ BPF_STX_MEM(BPF_W, BPF_REG_10, BPF_REG_0, -4),/* *(u32 *)(fp - 4) = r0 */ BPF_MOV64_REG(BPF_REG_2, BPF_REG_10), /* r2 = fp */ BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -4), /* r2 = r2 - 4 */ BPF_LD_MAP_FD(BPF_REG_1, map_fd), /* r1 = map_fd */ BPF_CALL_FUNC(BPF_FUNC_map_lookup_elem), /* r0 = map_lookup(r1, r2) */ BPF_JMP_IMM(BPF_JEQ, BPF_REG_0, 0, 2), /* if (r0 == 0) goto pc+2 */ BPF_MOV64_IMM(BPF_REG_1, 1), /* r1 = 1 */ BPF_XADD(BPF_DW, BPF_REG_0, BPF_REG_1, 0, 0), /* lock *(u64 *)r0 += r1 */ BPF_MOV64_IMM(BPF_REG_0, 0), /* r0 = 0 */ BPF_EXIT_INSN(), /* return r0 */ }; prog_fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET, prog, sizeof(prog), "GPL"); assert(prog_fd >= 0); sock = open_raw_sock("lo"); assert(setsockopt(sock, SOL_SOCKET, SO_ATTACH_BPF, &prog_fd, sizeof(prog_fd)) == 0); for (;;) { key = 6; assert(bpf_lookup_elem(map_fd, &key, &tcp_cnt) == 0); key = 17; assert(bpf_lookup_elem(map_fd, &key, &udp_cnt) == 0); printf("TCP %lld UDP %lld packets0, tcp_cnt, udp_cnt); sleep(1); } return 0; } RETURN VALUE For a successful call, the return value depends on the operation: BPF_MAP_CREATE The new file descriptor associated with eBPF map. BPF_PROG_LOAD The new file descriptor associated with eBPF program. All other commands Zero. On error, -1 is returned, and errno is set appropriately. ERRORS EPERM bpf() syscall was made without sufficient privilege (without the CAP_SYS_ADMIN capability). ENOMEM Cannot allocate sufficient memory. EBADF fd is not an open file descriptor EFAULT One of the pointers ( key or value or log_buf or insns ) is outside accessible address space. EINVAL The value specified in cmd is not recognized by this kernel. EINVAL For BPF_MAP_CREATE, either map_type or attributes are invalid. EINVAL For BPF_MAP_*_ELEM commands, some of the fields of "union bpf_attr" unused by this command are not set to zero. EINVAL For BPF_PROG_LOAD, attempt to load invalid program (unrecognized instruction or uses reserved fields or jumps out of range or loop detected or calls unknown function). EACCES For BPF_PROG_LOAD, though program has valid instructions, it was rejected, since it was deemed unsafe (may access disallowed memory region or uninitialized stack/register or function constraints don't match actual types or misaligned access). In such case it is recommended to call bpf() again with log_level = 1 and examine log_buf for specific reason provided by verifier. ENOENT For BPF_MAP_LOOKUP_ELEM or BPF_MAP_DELETE_ELEM, indicates that element with given key was not found. E2BIG program is too large or a map reached max_entries limit (max number of elements). NOTES These commands may be used only by a privileged process (one having the CAP_SYS_ADMIN capability). SEE ALSO eBPF architecture and instruction set is explained in Documentation/networking/filter.txt Linux 2014-09-16 BPF(2) ==================== Signed-off-by: David S. Miller <davem@davemloft.net> |
||
|---|---|---|
| arch | ||
| block | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| firmware | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt/kvm | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
| REPORTING-BUGS | ||
Linux kernel release 3.x <http://kernel.org/>
These are the release notes for Linux version 3. Read them carefully,
as they tell you what this is all about, explain how to install the
kernel, and what to do if something goes wrong.
WHAT IS LINUX?
Linux is a clone of the operating system Unix, written from scratch by
Linus Torvalds with assistance from a loosely-knit team of hackers across
the Net. It aims towards POSIX and Single UNIX Specification compliance.
It has all the features you would expect in a modern fully-fledged Unix,
including true multitasking, virtual memory, shared libraries, demand
loading, shared copy-on-write executables, proper memory management,
and multistack networking including IPv4 and IPv6.
It is distributed under the GNU General Public License - see the
accompanying COPYING file for more details.
ON WHAT HARDWARE DOES IT RUN?
Although originally developed first for 32-bit x86-based PCs (386 or higher),
today Linux also runs on (at least) the Compaq Alpha AXP, Sun SPARC and
UltraSPARC, Motorola 68000, PowerPC, PowerPC64, ARM, Hitachi SuperH, Cell,
IBM S/390, MIPS, HP PA-RISC, Intel IA-64, DEC VAX, AMD x86-64, AXIS CRIS,
Xtensa, Tilera TILE, AVR32 and Renesas M32R architectures.
Linux is easily portable to most general-purpose 32- or 64-bit architectures
as long as they have a paged memory management unit (PMMU) and a port of the
GNU C compiler (gcc) (part of The GNU Compiler Collection, GCC). Linux has
also been ported to a number of architectures without a PMMU, although
functionality is then obviously somewhat limited.
Linux has also been ported to itself. You can now run the kernel as a
userspace application - this is called UserMode Linux (UML).
DOCUMENTATION:
- There is a lot of documentation available both in electronic form on
the Internet and in books, both Linux-specific and pertaining to
general UNIX questions. I'd recommend looking into the documentation
subdirectories on any Linux FTP site for the LDP (Linux Documentation
Project) books. This README is not meant to be documentation on the
system: there are much better sources available.
- There are various README files in the Documentation/ subdirectory:
these typically contain kernel-specific installation notes for some
drivers for example. See Documentation/00-INDEX for a list of what
is contained in each file. Please read the Changes file, as it
contains information about the problems, which may result by upgrading
your kernel.
- The Documentation/DocBook/ subdirectory contains several guides for
kernel developers and users. These guides can be rendered in a
number of formats: PostScript (.ps), PDF, HTML, & man-pages, among others.
After installation, "make psdocs", "make pdfdocs", "make htmldocs",
or "make mandocs" will render the documentation in the requested format.
INSTALLING the kernel source:
- If you install the full sources, put the kernel tarball in a
directory where you have permissions (eg. your home directory) and
unpack it:
gzip -cd linux-3.X.tar.gz | tar xvf -
or
bzip2 -dc linux-3.X.tar.bz2 | tar xvf -
Replace "X" with the version number of the latest kernel.
Do NOT use the /usr/src/linux area! This area has a (usually
incomplete) set of kernel headers that are used by the library header
files. They should match the library, and not get messed up by
whatever the kernel-du-jour happens to be.
- You can also upgrade between 3.x releases by patching. Patches are
distributed in the traditional gzip and the newer bzip2 format. To
install by patching, get all the newer patch files, enter the
top level directory of the kernel source (linux-3.X) and execute:
gzip -cd ../patch-3.x.gz | patch -p1
or
bzip2 -dc ../patch-3.x.bz2 | patch -p1
Replace "x" for all versions bigger than the version "X" of your current
source tree, _in_order_, and you should be ok. You may want to remove
the backup files (some-file-name~ or some-file-name.orig), and make sure
that there are no failed patches (some-file-name# or some-file-name.rej).
If there are, either you or I have made a mistake.
Unlike patches for the 3.x kernels, patches for the 3.x.y kernels
(also known as the -stable kernels) are not incremental but instead apply
directly to the base 3.x kernel. For example, if your base kernel is 3.0
and you want to apply the 3.0.3 patch, you must not first apply the 3.0.1
and 3.0.2 patches. Similarly, if you are running kernel version 3.0.2 and
want to jump to 3.0.3, you must first reverse the 3.0.2 patch (that is,
patch -R) _before_ applying the 3.0.3 patch. You can read more on this in
Documentation/applying-patches.txt
Alternatively, the script patch-kernel can be used to automate this
process. It determines the current kernel version and applies any
patches found.
linux/scripts/patch-kernel linux
The first argument in the command above is the location of the
kernel source. Patches are applied from the current directory, but
an alternative directory can be specified as the second argument.
- Make sure you have no stale .o files and dependencies lying around:
cd linux
make mrproper
You should now have the sources correctly installed.
SOFTWARE REQUIREMENTS
Compiling and running the 3.x kernels requires up-to-date
versions of various software packages. Consult
Documentation/Changes for the minimum version numbers required
and how to get updates for these packages. Beware that using
excessively old versions of these packages can cause indirect
errors that are very difficult to track down, so don't assume that
you can just update packages when obvious problems arise during
build or operation.
BUILD directory for the kernel:
When compiling the kernel, all output files will per default be
stored together with the kernel source code.
Using the option "make O=output/dir" allow you to specify an alternate
place for the output files (including .config).
Example:
kernel source code: /usr/src/linux-3.X
build directory: /home/name/build/kernel
To configure and build the kernel, use:
cd /usr/src/linux-3.X
make O=/home/name/build/kernel menuconfig
make O=/home/name/build/kernel
sudo make O=/home/name/build/kernel modules_install install
Please note: If the 'O=output/dir' option is used, then it must be
used for all invocations of make.
CONFIGURING the kernel:
Do not skip this step even if you are only upgrading one minor
version. New configuration options are added in each release, and
odd problems will turn up if the configuration files are not set up
as expected. If you want to carry your existing configuration to a
new version with minimal work, use "make oldconfig", which will
only ask you for the answers to new questions.
- Alternative configuration commands are:
"make config" Plain text interface.
"make menuconfig" Text based color menus, radiolists & dialogs.
"make nconfig" Enhanced text based color menus.
"make xconfig" X windows (Qt) based configuration tool.
"make gconfig" X windows (Gtk) based configuration tool.
"make oldconfig" Default all questions based on the contents of
your existing ./.config file and asking about
new config symbols.
"make silentoldconfig"
Like above, but avoids cluttering the screen
with questions already answered.
Additionally updates the dependencies.
"make olddefconfig"
Like above, but sets new symbols to their default
values without prompting.
"make defconfig" Create a ./.config file by using the default
symbol values from either arch/$ARCH/defconfig
or arch/$ARCH/configs/${PLATFORM}_defconfig,
depending on the architecture.
"make ${PLATFORM}_defconfig"
Create a ./.config file by using the default
symbol values from
arch/$ARCH/configs/${PLATFORM}_defconfig.
Use "make help" to get a list of all available
platforms of your architecture.
"make allyesconfig"
Create a ./.config file by setting symbol
values to 'y' as much as possible.
"make allmodconfig"
Create a ./.config file by setting symbol
values to 'm' as much as possible.
"make allnoconfig" Create a ./.config file by setting symbol
values to 'n' as much as possible.
"make randconfig" Create a ./.config file by setting symbol
values to random values.
"make localmodconfig" Create a config based on current config and
loaded modules (lsmod). Disables any module
option that is not needed for the loaded modules.
To create a localmodconfig for another machine,
store the lsmod of that machine into a file
and pass it in as a LSMOD parameter.
target$ lsmod > /tmp/mylsmod
target$ scp /tmp/mylsmod host:/tmp
host$ make LSMOD=/tmp/mylsmod localmodconfig
The above also works when cross compiling.
"make localyesconfig" Similar to localmodconfig, except it will convert
all module options to built in (=y) options.
You can find more information on using the Linux kernel config tools
in Documentation/kbuild/kconfig.txt.
- NOTES on "make config":
- Having unnecessary drivers will make the kernel bigger, and can
under some circumstances lead to problems: probing for a
nonexistent controller card may confuse your other controllers
- Compiling the kernel with "Processor type" set higher than 386
will result in a kernel that does NOT work on a 386. The
kernel will detect this on bootup, and give up.
- A kernel with math-emulation compiled in will still use the
coprocessor if one is present: the math emulation will just
never get used in that case. The kernel will be slightly larger,
but will work on different machines regardless of whether they
have a math coprocessor or not.
- The "kernel hacking" configuration details usually result in a
bigger or slower kernel (or both), and can even make the kernel
less stable by configuring some routines to actively try to
break bad code to find kernel problems (kmalloc()). Thus you
should probably answer 'n' to the questions for "development",
"experimental", or "debugging" features.
COMPILING the kernel:
- Make sure you have at least gcc 3.2 available.
For more information, refer to Documentation/Changes.
Please note that you can still run a.out user programs with this kernel.
- Do a "make" to create a compressed kernel image. It is also
possible to do "make install" if you have lilo installed to suit the
kernel makefiles, but you may want to check your particular lilo setup first.
To do the actual install, you have to be root, but none of the normal
build should require that. Don't take the name of root in vain.
- If you configured any of the parts of the kernel as `modules', you
will also have to do "make modules_install".
- Verbose kernel compile/build output:
Normally, the kernel build system runs in a fairly quiet mode (but not
totally silent). However, sometimes you or other kernel developers need
to see compile, link, or other commands exactly as they are executed.
For this, use "verbose" build mode. This is done by inserting
"V=1" in the "make" command. E.g.:
make V=1 all
To have the build system also tell the reason for the rebuild of each
target, use "V=2". The default is "V=0".
- Keep a backup kernel handy in case something goes wrong. This is
especially true for the development releases, since each new release
contains new code which has not been debugged. Make sure you keep a
backup of the modules corresponding to that kernel, as well. If you
are installing a new kernel with the same version number as your
working kernel, make a backup of your modules directory before you
do a "make modules_install".
Alternatively, before compiling, use the kernel config option
"LOCALVERSION" to append a unique suffix to the regular kernel version.
LOCALVERSION can be set in the "General Setup" menu.
- In order to boot your new kernel, you'll need to copy the kernel
image (e.g. .../linux/arch/i386/boot/bzImage after compilation)
to the place where your regular bootable kernel is found.
- Booting a kernel directly from a floppy without the assistance of a
bootloader such as LILO, is no longer supported.
If you boot Linux from the hard drive, chances are you use LILO, which
uses the kernel image as specified in the file /etc/lilo.conf. The
kernel image file is usually /vmlinuz, /boot/vmlinuz, /bzImage or
/boot/bzImage. To use the new kernel, save a copy of the old image
and copy the new image over the old one. Then, you MUST RERUN LILO
to update the loading map!! If you don't, you won't be able to boot
the new kernel image.
Reinstalling LILO is usually a matter of running /sbin/lilo.
You may wish to edit /etc/lilo.conf to specify an entry for your
old kernel image (say, /vmlinux.old) in case the new one does not
work. See the LILO docs for more information.
After reinstalling LILO, you should be all set. Shutdown the system,
reboot, and enjoy!
If you ever need to change the default root device, video mode,
ramdisk size, etc. in the kernel image, use the 'rdev' program (or
alternatively the LILO boot options when appropriate). No need to
recompile the kernel to change these parameters.
- Reboot with the new kernel and enjoy.
IF SOMETHING GOES WRONG:
- If you have problems that seem to be due to kernel bugs, please check
the file MAINTAINERS to see if there is a particular person associated
with the part of the kernel that you are having trouble with. If there
isn't anyone listed there, then the second best thing is to mail
them to me (torvalds@linux-foundation.org), and possibly to any other
relevant mailing-list or to the newsgroup.
- In all bug-reports, *please* tell what kernel you are talking about,
how to duplicate the problem, and what your setup is (use your common
sense). If the problem is new, tell me so, and if the problem is
old, please try to tell me when you first noticed it.
- If the bug results in a message like
unable to handle kernel paging request at address C0000010
Oops: 0002
EIP: 0010:XXXXXXXX
eax: xxxxxxxx ebx: xxxxxxxx ecx: xxxxxxxx edx: xxxxxxxx
esi: xxxxxxxx edi: xxxxxxxx ebp: xxxxxxxx
ds: xxxx es: xxxx fs: xxxx gs: xxxx
Pid: xx, process nr: xx
xx xx xx xx xx xx xx xx xx xx
or similar kernel debugging information on your screen or in your
system log, please duplicate it *exactly*. The dump may look
incomprehensible to you, but it does contain information that may
help debugging the problem. The text above the dump is also
important: it tells something about why the kernel dumped code (in
the above example, it's due to a bad kernel pointer). More information
on making sense of the dump is in Documentation/oops-tracing.txt
- If you compiled the kernel with CONFIG_KALLSYMS you can send the dump
as is, otherwise you will have to use the "ksymoops" program to make
sense of the dump (but compiling with CONFIG_KALLSYMS is usually preferred).
This utility can be downloaded from
ftp://ftp.<country>.kernel.org/pub/linux/utils/kernel/ksymoops/ .
Alternatively, you can do the dump lookup by hand:
- In debugging dumps like the above, it helps enormously if you can
look up what the EIP value means. The hex value as such doesn't help
me or anybody else very much: it will depend on your particular
kernel setup. What you should do is take the hex value from the EIP
line (ignore the "0010:"), and look it up in the kernel namelist to
see which kernel function contains the offending address.
To find out the kernel function name, you'll need to find the system
binary associated with the kernel that exhibited the symptom. This is
the file 'linux/vmlinux'. To extract the namelist and match it against
the EIP from the kernel crash, do:
nm vmlinux | sort | less
This will give you a list of kernel addresses sorted in ascending
order, from which it is simple to find the function that contains the
offending address. Note that the address given by the kernel
debugging messages will not necessarily match exactly with the
function addresses (in fact, that is very unlikely), so you can't
just 'grep' the list: the list will, however, give you the starting
point of each kernel function, so by looking for the function that
has a starting address lower than the one you are searching for but
is followed by a function with a higher address you will find the one
you want. In fact, it may be a good idea to include a bit of
"context" in your problem report, giving a few lines around the
interesting one.
If you for some reason cannot do the above (you have a pre-compiled
kernel image or similar), telling me as much about your setup as
possible will help. Please read the REPORTING-BUGS document for details.
- Alternatively, you can use gdb on a running kernel. (read-only; i.e. you
cannot change values or set break points.) To do this, first compile the
kernel with -g; edit arch/i386/Makefile appropriately, then do a "make
clean". You'll also need to enable CONFIG_PROC_FS (via "make config").
After you've rebooted with the new kernel, do "gdb vmlinux /proc/kcore".
You can now use all the usual gdb commands. The command to look up the
point where your system crashed is "l *0xXXXXXXXX". (Replace the XXXes
with the EIP value.)
gdb'ing a non-running kernel currently fails because gdb (wrongly)
disregards the starting offset for which the kernel is compiled.