参考内核文档: Documentation/printk-formats.txt
在内核中使用dump_stack的时候可以看到如下用法：
static inline void print_ip_sym(unsigned long ip){ printk("[<%px>] %pS\n", (void *) ip, (void *) ip);} 然后我们就可以看到类似如下的内核log：
可以看到，上面不光输出了运行地址，还把对应的函数名以及偏移地址都列了出来，内核是如何做到的呢？
在调用printk的时候：
printk --> vprintk_default --> vprintk_emit --> vprintk_store --> vscnprintf --> vsnprintf --> pointer
上面的转换就是在pointer中完成的：
1 /* 2 * Show a '%p' thing. A kernel extension is that the '%p' is followed 3 * by an extra set of alphanumeric characters that are extended format 4 * specifiers. 5 * 6 * Please update scripts/checkpatch.pl when adding/removing conversion 7 * characters. (Search for "check for vsprintf extension"). 8 * 9 * Right now we handle: 10 * 11 * - 'F' For symbolic function descriptor pointers with offset 12 * - 'f' For simple symbolic function names without offset 13 * - 'S' For symbolic direct pointers with offset 14 * - 's' For symbolic direct pointers without offset 15 * - '[FfSs]R' as above with __builtin_extract_return_addr() translation 16 * - 'B' For backtraced symbolic direct pointers with offset 17 * - 'R' For decoded struct resource, e.g., [mem 0x0-0x1f 64bit pref] 18 * - 'r' For raw struct resource, e.g., [mem 0x0-0x1f flags 0x201] 19 * - 'b[l]' For a bitmap, the number of bits is determined by the field 20 * width which must be explicitly specified either as part of the 21 * format string '%32b[l]' or through '%*b[l]', [l] selects 22 * range-list format instead of hex format 23 * - 'M' For a 6-byte MAC address, it prints the address in the 24 * usual colon-separated hex notation 25 * - 'm' For a 6-byte MAC address, it prints the hex address without colons 26 * - 'MF' For a 6-byte MAC FDDI address, it prints the address 27 * with a dash-separated hex notation 28 * - '[mM]R' For a 6-byte MAC address, Reverse order (Bluetooth) 29 * - 'I' [46] for IPv4/IPv6 addresses printed in the usual way 30 * IPv4 uses dot-separated decimal without leading 0's (1.2.3.4) 31 * IPv6 uses colon separated network-order 16 bit hex with leading 0's 32 * [S][pfs] 33 * Generic IPv4/IPv6 address (struct sockaddr *) that falls back to 34 * [4] or [6] and is able to print port [p], flowinfo [f], scope [s] 35 * - 'i' [46] for 'raw' IPv4/IPv6 addresses 36 * IPv6 omits the colons (01020304...0f) 37 * IPv4 uses dot-separated decimal with leading 0's (010.123.045.006) 38 * [S][pfs] 39 * Generic IPv4/IPv6 address (struct sockaddr *) that falls back to 40 * [4] or [6] and is able to print port [p], flowinfo [f], scope [s] 41 * - '[Ii][4S][hnbl]' IPv4 addresses in host, network, big or little endian order 42 * - 'I[6S]c' for IPv6 addresses printed as specified by 43 * http://tools.ietf.org/html/rfc5952 44 * - 'E[achnops]' For an escaped buffer, where rules are defined by combination 45 * of the following flags (see string_escape_mem() for the 46 * details): 47 * a - ESCAPE_ANY 48 * c - ESCAPE_SPECIAL 49 * h - ESCAPE_HEX 50 * n - ESCAPE_NULL 51 * o - ESCAPE_OCTAL 52 * p - ESCAPE_NP 53 * s - ESCAPE_SPACE 54 * By default ESCAPE_ANY_NP is used. 55 * - 'U' For a 16 byte UUID/GUID, it prints the UUID/GUID in the form 56 * "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx" 57 * Options for %pU are: 58 * b big endian lower case hex (default) 59 * B big endian UPPER case hex 60 * l little endian lower case hex 61 * L little endian UPPER case hex 62 * big endian output byte order is: 63 * [0][1][2][3]-[4][5]-[6][7]-[8][9]-[10][11][12][13][14][15] 64 * little endian output byte order is: 65 * [3][2][1][0]-[5][4]-[7][6]-[8][9]-[10][11][12][13][14][15] 66 * - 'V' For a struct va_format which contains a format string * and va_list *, 67 * call vsnprintf(->format, *->va_list). 68 * Implements a "recursive vsnprintf". 69 * Do not use this feature without some mechanism to verify the 70 * correctness of the format string and va_list arguments. 71 * - 'K' For a kernel pointer that should be hidden from unprivileged users 72 * - 'NF' For a netdev_features_t 73 * - 'h[CDN]' For a variable-length buffer, it prints it as a hex string with 74 * a certain separator (' ' by default): 75 * C colon 76 * D dash 77 * N no separator 78 * The maximum supported length is 64 bytes of the input. Consider 79 * to use print_hex_dump() for the larger input. 80 * - 'a[pd]' For address types [p] phys_addr_t, [d] dma_addr_t and derivatives 81 * (default assumed to be phys_addr_t, passed by reference) 82 * - 'd[234]' For a dentry name (optionally 2-4 last components) 83 * - 'D[234]' Same as 'd' but for a struct file 84 * - 'g' For block_device name (gendisk + partition number) 85 * - 'C' For a clock, it prints the name (Common Clock Framework) or address 86 * (legacy clock framework) of the clock 87 * - 'Cn' For a clock, it prints the name (Common Clock Framework) or address 88 * (legacy clock framework) of the clock 89 * - 'Cr' For a clock, it prints the current rate of the clock 90 * - 'G' For flags to be printed as a collection of symbolic strings that would 91 * construct the specific value. Supported flags given by option: 92 * p page flags (see struct page) given as pointer to unsigned long 93 * g gfp flags (GFP_* and __GFP_*) given as pointer to gfp_t 94 * v vma flags (VM_*) given as pointer to unsigned long 95 * - 'O' For a kobject based struct. Must be one of the following: 96 * - 'OF[fnpPcCF]' For a device tree object 97 * Without any optional arguments prints the full_name 98 * f device node full_name 99 * n device node name100 * p device node phandle101 * P device node path spec (name + @unit)102 * F device node flags103 * c major compatible string104 * C full compatible string105 *106 * ** Please update also Documentation/printk-formats.txt when making changes **107 *108 * Note: The difference between 'S' and 'F' is that on ia64 and ppc64109 * function pointers are really function descriptors, which contain a110 * pointer to the real address.111 */112 static noinline_for_stack113 char *pointer(const char *fmt, char *buf, char *end, void *ptr,114 struct printf_spec spec)115 {116 const int default_width = 2 * sizeof(void *);117 118 if (!ptr && *fmt != 'K') {119 /*120 * Print (null) with the same width as a pointer so it makes121 * tabular output look nice.122 */123 if (spec.field_width == -1)124 spec.field_width = default_width;125 return string(buf, end, "(null)", spec);126 }127 128 switch (*fmt) {129 case 'F':130 case 'f':131 ptr = dereference_function_descriptor(ptr);132 /* Fallthrough */133 case 'S':134 case 's':135 case 'B':136 return symbol_string(buf, end, ptr, spec, fmt);137 case 'R':138 case 'r':139 return resource_string(buf, end, ptr, spec, fmt);140 case 'h':141 return hex_string(buf, end, ptr, spec, fmt);142 case 'b':143 switch (fmt[1]) {144 case 'l':145 return bitmap_list_string(buf, end, ptr, spec, fmt);146 default:147 return bitmap_string(buf, end, ptr, spec, fmt);148 }149 case 'M': /* Colon separated: 00:01:02:03:04:05 */150 case 'm': /* Contiguous: 000102030405 */151 /* [mM]F (FDDI) */152 /* [mM]R (Reverse order; Bluetooth) */153 return mac_address_string(buf, end, ptr, spec, fmt);154 case 'I': /* Formatted IP supported155 * 4: 1.2.3.4156 * 6: 0001:0203:...:0708157 * 6c: 1::708 or 1::1.2.3.4158 */159 case 'i': /* Contiguous:160 * 4: 001.002.003.004161 * 6: 000102...0f162 */163 switch (fmt[1]) {164 case '6':165 return ip6_addr_string(buf, end, ptr, spec, fmt);166 case '4':167 return ip4_addr_string(buf, end, ptr, spec, fmt);168 case 'S': {169 const union {170 struct sockaddr raw;171 struct sockaddr_in v4;172 struct sockaddr_in6 v6;173 } *sa = ptr;174 175 switch (sa->raw.sa_family) {176 case AF_INET:177 return ip4_addr_string_sa(buf, end, &sa->v4, spec, fmt);178 case AF_INET6:179 return ip6_addr_string_sa(buf, end, &sa->v6, spec, fmt);180 default:181 return string(buf, end, "(invalid address)", spec);182 }}183 }184 break;185 case 'E':186 return escaped_string(buf, end, ptr, spec, fmt);187 case 'U':188 return uuid_string(buf, end, ptr, spec, fmt);189 case 'V':190 {191 va_list va;192 193 va_copy(va, *((struct va_format *)ptr)->va);194 buf += vsnprintf(buf, end > buf ? end - buf : 0,195 ((struct va_format *)ptr)->fmt, va);196 va_end(va);197 return buf;198 }199 case 'K':200 switch (kptr_restrict) {201 case 0:202 /* Always print %pK values */203 break;204 case 1: {205 const struct cred *cred;206 207 /*208 * kptr_restrict==1 cannot be used in IRQ context209 * because its test for CAP_SYSLOG would be meaningless.210 */211 if (in_irq() || in_serving_softirq() || in_nmi()) {212 if (spec.field_width == -1)213 spec.field_width = default_width;214 return string(buf, end, "pK-error", spec);215 }216 217 /*218 * Only print the real pointer value if the current219 * process has CAP_SYSLOG and is running with the220 * same credentials it started with. This is because221 * access to files is checked at open() time, but %pK222 * checks permission at read() time. We don't want to223 * leak pointer values if a binary opens a file using224 * %pK and then elevates privileges before reading it.225 */226 cred = current_cred();227 if (!has_capability_noaudit(current, CAP_SYSLOG) ||228 !uid_eq(cred->euid, cred->uid) ||229 !gid_eq(cred->egid, cred->gid))230 ptr = NULL;231 break;232 }233 case 2:234 default:235 /* Always print 0's for %pK */236 ptr = NULL;237 break;238 }239 break;240 241 case 'N':242 return netdev_bits(buf, end, ptr, fmt);243 case 'a':244 return address_val(buf, end, ptr, fmt);245 case 'd':246 return dentry_name(buf, end, ptr, spec, fmt);247 case 'C':248 return clock(buf, end, ptr, spec, fmt);249 case 'D':250 return dentry_name(buf, end,251 ((const struct file *)ptr)->f_path.dentry,252 spec, fmt);253 #ifdef CONFIG_BLOCK254 case 'g':255 return bdev_name(buf, end, ptr, spec, fmt);256 #endif257 258 case 'G':259 return flags_string(buf, end, ptr, fmt);260 case 'O':261 switch (fmt[1]) {262 case 'F':263 return device_node_string(buf, end, ptr, spec, fmt + 1);264 }265 }266 spec.flags |= SMALL;267 if (spec.field_width == -1) {268 spec.field_width = default_width;269 spec.flags |= ZEROPAD;270 }271 spec.base = 16;272 273 return number(buf, end, (unsigned long) ptr, spec);274 } 第136行， symbol_string(buf, end, ptr, spec, fmt);
1 static noinline_for_stack 2 char *symbol_string(char *buf, char *end, void *ptr, 3 struct printf_spec spec, const char *fmt) 4 { 5 unsigned long value; 6 #ifdef CONFIG_KALLSYMS 7 char sym[KSYM_SYMBOL_LEN]; 8 #endif 9 10 if (fmt[1] == 'R')11 ptr = __builtin_extract_return_addr(ptr);12 value = (unsigned long)ptr;13 14 #ifdef CONFIG_KALLSYMS15 if (*fmt == 'B')16 sprint_backtrace(sym, value);17 else if (*fmt != 'f' && *fmt != 's')18 sprint_symbol(sym, value);19 else20 sprint_symbol_no_offset(sym, value);21 22 return string(buf, end, sym, spec);23 #else24 return special_hex_number(buf, end, value, sizeof(void *));25 #endif26 } 第20行：sprint_symbol_no_offset
1 /** 2 * sprint_symbol_no_offset - Look up a kernel symbol and return it in a text buffer 3 * @buffer: buffer to be stored 4 * @address: address to lookup 5 * 6 * This function looks up a kernel symbol with @address and stores its name 7 * and module name to @buffer if possible. If no symbol was found, just saves 8 * its @address as is. 9 *10 * This function returns the number of bytes stored in @buffer.11 */12 int sprint_symbol_no_offset(char *buffer, unsigned long address)13 {14 return __sprint_symbol(buffer, address, 0, 0);15 }
完。