eBPF：c语言内存分区

内存分区

(高地址)

栈区

堆区

未初始化(或初始值为0)的全局变量和静态变量 (.bss)

初始化的全局变量和静态变量 (.data)

常量区 (.rodata)

代码区

(低地址)

bss: block started by symbol
rodata: read-only data

代码

sum.c

1	$ cat sum.c

int sum(int a, int b)
{
  static int val_1;
  static int val_2 = 0;
  static int val_3 = 1;
  static int val_4 = 0;
  static int val_5 = 2;
  const static int val_6 = 0;
  return a + b;
}

生成可重定位目标文件 sum.o

1	$ g++ -c sum.cpp -o sum.o

查看 sum.o 的段头表

1	$ readelf -S sum.o

There are 13 section headers, starting at offset 0x2a0:

Section Headers:
  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [ 0]                   NULL             0000000000000000  00000000
       0000000000000000  0000000000000000           0     0     0
  [ 1] .text             PROGBITS         0000000000000000  00000040
       0000000000000018  0000000000000000  AX       0     0     1
  [ 2] .data             PROGBITS         0000000000000000  00000058
       0000000000000008  0000000000000000  WA       0     0     4
  [ 3] .bss              NOBITS           0000000000000000  00000060
       000000000000000c  0000000000000000  WA       0     0     4
  [ 4] .rodata           PROGBITS         0000000000000000  00000060
       0000000000000004  0000000000000000   A       0     0     4
  [ 5] .comment          PROGBITS         0000000000000000  00000064
       000000000000002c  0000000000000001  MS       0     0     1
  [ 6] .note.GNU-stack   PROGBITS         0000000000000000  00000090
       0000000000000000  0000000000000000           0     0     1
  [ 7] .note.gnu.pr[...] NOTE             0000000000000000  00000090
       0000000000000020  0000000000000000   A       0     0     8
  [ 8] .eh_frame         PROGBITS         0000000000000000  000000b0
       0000000000000038  0000000000000000   A       0     0     8
  [ 9] .rela.eh_frame    RELA             0000000000000000  00000218
       0000000000000018  0000000000000018   I      10     8     8
  [10] .symtab           SYMTAB           0000000000000000  000000e8
       00000000000000f0  0000000000000018          11     9     8
  [11] .strtab           STRTAB           0000000000000000  000001d8
       000000000000003b  0000000000000000           0     0     1
  [12] .shstrtab         STRTAB           0000000000000000  00000230
       000000000000006f  0000000000000000           0     0     1
Key to Flags:
  W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
  L (link order), O (extra OS processing required), G (group), T (TLS),
  C (compressed), x (unknown), o (OS specific), E (exclude),
  D (mbind), l (large), p (processor specific)

.data

大小为 8 字节
在目标文件中占用 8 字节 (00000058 - 00000060)
val_3, val_5

.bss

大小为 12 字节
在目标文件中占用 0 字节 (00000060 - 00000060)
val_1, val_2, val_4

.rodata

大小为 4 字节
在目标文件中占用 4 字节 (00000060 - 00000064)
val_6