关于c语言中文字字符串的内存分配问题
我是一个刚开始用C语言学习计算机系统的学生 我有一个关于文字字符串的内存分配工作原理的问题 我尝试使用以下代码分析如何在内存系统中分配字符串文字：关于c语言中文字字符串的内存分配问题,c,memory,string-literals,C,Memory,String Literals,我是一个刚开始用C语言学习计算机系统的学生 我有一个关于文字字符串的内存分配工作原理的问题 我尝试使用以下代码分析如何在内存系统中分配字符串文字： #include <stdio.h> int main(){ char *p = "1"; printf("%s\n", p); printf("%p\n", p); p = "2"; printf("%s\n&qu
#include <stdio.h>
int main(){
char *p = "1";
printf("%s\n", p);
printf("%p\n", p);
p = "2";
printf("%s\n", p);
printf("%p\n", p);
p = "3";
printf("%s\n", p);
printf("%p\n", p);
p = "4";
printf("%s\n", p);
printf("%p\n", p);
}
这两个字符串之间是否分配了某些内容？或者系统有什么理由这样分配字符串？间距也包括printf格式字符串：
0000000000404000 "1\0"
0000000000404002 "%s\n\0"
0000000000404006 "%p\n\0"
000000000040400A "2\0"
000000000040400C "3\0"
000000000040400E "4\0"
请注意，字符串的显示顺序与它们在源代码中的显示顺序相同，但printf格式字符串不会在每次调用中重复。由于字符串相同，它们只需在可执行文件中出现一次。间距也包括printf格式字符串：
0000000000404000 "1\0"
0000000000404002 "%s\n\0"
0000000000404006 "%p\n\0"
000000000040400A "2\0"
000000000040400C "3\0"
000000000040400E "4\0"
请注意，字符串的显示顺序与它们在源代码中的显示顺序相同，但printf格式字符串不会在每次调用中重复。由于字符串是相同的，它们只需要在可执行文件中出现一次。但位大小并不总是“8位”，这取决于操作系统 我们可以将可执行文件诊断为代码段，以获得其地址分配 查看CentOS的结果，如下所示，
添加[root@localhost zz]# ./a.out
1
0x4006e8
2
0x4006f8
3
0x400700
4
0x400708
[root@localhost zz]# objdump -d a.out
a.out: file format elf64-littleaarch64
Disassembly of section .init:
0000000000400408 <_init>:
400408: a9bf7bfd stp x29, x30, [sp,#-16]!
40040c: 910003fd mov x29, sp
400410: 94000032 bl 4004d8 <call_weak_fn>
400414: a8c17bfd ldp x29, x30, [sp],#16
400418: d65f03c0 ret
Disassembly of section .plt:
0000000000400420 <.plt>:
400420: a9bf7bf0 stp x16, x30, [sp,#-16]!
400424: f00000f0 adrp x16, 41f000 <__FRAME_END__+0x1e8f4>
400428: f947fe11 ldr x17, [x16,#4088]
40042c: 913fe210 add x16, x16, #0xff8
400430: d61f0220 br x17
400434: d503201f nop
400438: d503201f nop
40043c: d503201f nop
0000000000400440 <__libc_start_main@plt>:
400440: 90000110 adrp x16, 420000 <__libc_start_main@GLIBC_2.17>
400444: f9400211 ldr x17, [x16]
400448: 91000210 add x16, x16, #0x0
40044c: d61f0220 br x17
0000000000400450 <__gmon_start__@plt>:
400450: 90000110 adrp x16, 420000 <__libc_start_main@GLIBC_2.17>
400454: f9400611 ldr x17, [x16,#8]
400458: 91002210 add x16, x16, #0x8
40045c: d61f0220 br x17
0000000000400460 <abort@plt>:
400460: 90000110 adrp x16, 420000 <__libc_start_main@GLIBC_2.17>
400464: f9400a11 ldr x17, [x16,#16]
400468: 91004210 add x16, x16, #0x10
40046c: d61f0220 br x17
0000000000400470 <puts@plt>:
400470: 90000110 adrp x16, 420000 <__libc_start_main@GLIBC_2.17>
400474: f9400e11 ldr x17, [x16,#24]
400478: 91006210 add x16, x16, #0x18
40047c: d61f0220 br x17
0000000000400480 <printf@plt>:
400480: 90000110 adrp x16, 420000 <__libc_start_main@GLIBC_2.17>
400484: f9401211 ldr x17, [x16,#32]
400488: 91008210 add x16, x16, #0x20
40048c: d61f0220 br x17
Disassembly of section .text:
0000000000400490 <_start>:
400490: d280001d mov x29, #0x0 // #0
400494: d280001e mov x30, #0x0 // #0
400498: 910003fd mov x29, sp
40049c: aa0003e5 mov x5, x0
4004a0: f94003e1 ldr x1, [sp]
4004a4: 910023e2 add x2, sp, #0x8
4004a8: 910003e6 mov x6, sp
4004ac: 580000a0 ldr x0, 4004c0 <_start+0x30>
4004b0: 580000c3 ldr x3, 4004c8 <_start+0x38>
4004b4: 580000e4 ldr x4, 4004d0 <_start+0x40>
4004b8: 97ffffe2 bl 400440 <__libc_start_main@plt>
4004bc: 97ffffe9 bl 400460 <abort@plt>
4004c0: 00400594 .word 0x00400594
4004c4: 00000000 .word 0x00000000
4004c8: 00400638 .word 0x00400638
4004cc: 00000000 .word 0x00000000
4004d0: 004006b8 .word 0x004006b8
4004d4: 00000000 .word 0x00000000
00000000004004d8 <call_weak_fn>:
4004d8: f00000e0 adrp x0, 41f000 <__FRAME_END__+0x1e8f4>
4004dc: f947f000 ldr x0, [x0,#4064]
4004e0: b4000040 cbz x0, 4004e8 <call_weak_fn+0x10>
4004e4: 17ffffdb b 400450 <__gmon_start__@plt>
4004e8: d65f03c0 ret
4004ec: 00000000 .inst 0x00000000 ; undefined
00000000004004f0 <deregister_tm_clones>:
4004f0: 90000100 adrp x0, 420000 <__libc_start_main@GLIBC_2.17>
4004f4: 9100e000 add x0, x0, #0x38
4004f8: 90000101 adrp x1, 420000 <__libc_start_main@GLIBC_2.17>
4004fc: 9100e021 add x1, x1, #0x38
400500: eb00003f cmp x1, x0
400504: 540000a0 b.eq 400518 <deregister_tm_clones+0x28>
400508: 90000001 adrp x1, 400000 <_init-0x408>
40050c: f9436c21 ldr x1, [x1,#1752]
400510: b4000041 cbz x1, 400518 <deregister_tm_clones+0x28>
400514: d61f0020 br x1
400518: d65f03c0 ret
40051c: d503201f nop
0000000000400520 <register_tm_clones>:
400520: 90000100 adrp x0, 420000 <__libc_start_main@GLIBC_2.17>
400524: 9100e000 add x0, x0, #0x38
400528: 90000101 adrp x1, 420000 <__libc_start_main@GLIBC_2.17>
40052c: 9100e021 add x1, x1, #0x38
400530: cb000021 sub x1, x1, x0
400534: 9343fc21 asr x1, x1, #3
400538: 8b41fc21 add x1, x1, x1, lsr #63
40053c: 9341fc21 asr x1, x1, #1
400540: b40000c1 cbz x1, 400558 <register_tm_clones+0x38>
400544: 90000002 adrp x2, 400000 <_init-0x408>
400548: f9437042 ldr x2, [x2,#1760]
40054c: b4000062 cbz x2, 400558 <register_tm_clones+0x38>
400550: d61f0040 br x2
400554: d503201f nop
400558: d65f03c0 ret
40055c: d503201f nop
0000000000400560 <__do_global_dtors_aux>:
400560: a9be7bfd stp x29, x30, [sp,#-32]!
400564: 910003fd mov x29, sp
400568: f9000bf3 str x19, [sp,#16]
40056c: 90000113 adrp x19, 420000 <__libc_start_main@GLIBC_2.17>
400570: 3940e260 ldrb w0, [x19,#56]
400574: 35000080 cbnz w0, 400584 <__do_global_dtors_aux+0x24>
400578: 97ffffde bl 4004f0 <deregister_tm_clones>
40057c: 52800020 mov w0, #0x1 // #1
400580: 3900e260 strb w0, [x19,#56]
400584: f9400bf3 ldr x19, [sp,#16]
400588: a8c27bfd ldp x29, x30, [sp],#32
40058c: d65f03c0 ret
0000000000400590 <frame_dummy>:
400590: 17ffffe4 b 400520 <register_tm_clones>
0000000000400594 <main>:
400594: a9be7bfd stp x29, x30, [sp,#-32]!
400598: 910003fd mov x29, sp
40059c: 90000000 adrp x0, 400000 <_init-0x408>
4005a0: 911ba000 add x0, x0, #0x6e8
4005a4: f9000fa0 str x0, [x29,#24]
4005a8: f9400fa0 ldr x0, [x29,#24]
4005ac: 97ffffb1 bl 400470 <puts@plt>
4005b0: 90000000 adrp x0, 400000 <_init-0x408>
4005b4: 911bc000 add x0, x0, #0x6f0
4005b8: f9400fa1 ldr x1, [x29,#24]
4005bc: 97ffffb1 bl 400480 <printf@plt>
4005c0: 90000000 adrp x0, 400000 <_init-0x408>
4005c4: 911be000 add x0, x0, #0x6f8
4005c8: f9000fa0 str x0, [x29,#24]
4005cc: f9400fa0 ldr x0, [x29,#24]
4005d0: 97ffffa8 bl 400470 <puts@plt>
4005d4: 90000000 adrp x0, 400000 <_init-0x408>
4005d8: 911bc000 add x0, x0, #0x6f0
4005dc: f9400fa1 ldr x1, [x29,#24]
4005e0: 97ffffa8 bl 400480 <printf@plt>
4005e4: 90000000 adrp x0, 400000 <_init-0x408>
4005e8: 911c0000 add x0, x0, #0x700
4005ec: f9000fa0 str x0, [x29,#24]
4005f0: f9400fa0 ldr x0, [x29,#24]
4005f4: 97ffff9f bl 400470 <puts@plt>
4005f8: 90000000 adrp x0, 400000 <_init-0x408>
4005fc: 911bc000 add x0, x0, #0x6f0
400600: f9400fa1 ldr x1, [x29,#24]
400604: 97ffff9f bl 400480 <printf@plt>
400608: 90000000 adrp x0, 400000 <_init-0x408>
40060c: 911c2000 add x0, x0, #0x708
400610: f9000fa0 str x0, [x29,#24]
400614: f9400fa0 ldr x0, [x29,#24]
400618: 97ffff96 bl 400470 <puts@plt>
40061c: 90000000 adrp x0, 400000 <_init-0x408>
400620: 911bc000 add x0, x0, #0x6f0
400624: f9400fa1 ldr x1, [x29,#24]
400628: 97ffff96 bl 400480 <printf@plt>
40062c: 52800000 mov w0, #0x0 // #0
400630: a8c27bfd ldp x29, x30, [sp],#32
400634: d65f03c0 ret
0000000000400638 <__libc_csu_init>:
400638: a9bc7bfd stp x29, x30, [sp,#-64]!
40063c: 910003fd mov x29, sp
400640: a901d7f4 stp x20, x21, [sp,#24]
400644: f00000f4 adrp x20, 41f000 <__FRAME_END__+0x1e8f4>
400648: f00000f5 adrp x21, 41f000 <__FRAME_END__+0x1e8f4>
40064c: 91380294 add x20, x20, #0xe00
400650: 9137e2b5 add x21, x21, #0xdf8
400654: a902dff6 stp x22, x23, [sp,#40]
400658: cb150294 sub x20, x20, x21
40065c: f9001ff8 str x24, [sp,#56]
400660: 9343fe94 asr x20, x20, #3
400664: 2a0003f6 mov w22, w0
400668: aa0103f7 mov x23, x1
40066c: aa0203f8 mov x24, x2
400670: 97ffff66 bl 400408 <_init>
400674: b4000194 cbz x20, 4006a4 <__libc_csu_init+0x6c>
400678: f9000bb3 str x19, [x29,#16]
40067c: d2800013 mov x19, #0x0 // #0
400680: f8737aa3 ldr x3, [x21,x19,lsl #3]
400684: aa1803e2 mov x2, x24
400688: aa1703e1 mov x1, x23
40068c: 2a1603e0 mov w0, w22
400690: 91000673 add x19, x19, #0x1
400694: d63f0060 blr x3
400698: eb13029f cmp x20, x19
40069c: 54ffff21 b.ne 400680 <__libc_csu_init+0x48>
4006a0: f9400bb3 ldr x19, [x29,#16]
4006a4: a941d7f4 ldp x20, x21, [sp,#24]
4006a8: a942dff6 ldp x22, x23, [sp,#40]
4006ac: f9401ff8 ldr x24, [sp,#56]
4006b0: a8c47bfd ldp x29, x30, [sp],#64
4006b4: d65f03c0 ret
00000000004006b8 <__libc_csu_fini>:
4006b8: d65f03c0 ret
Disassembly of section .fini:
00000000004006bc <_fini>:
4006bc: a9bf7bfd stp x29, x30, [sp,#-16]!
4006c0: 910003fd mov x29, sp
4006c4: a8c17bfd ldp x29, x30, [sp],#16
4006c8: d65f03c0 ret
[root@localhost#/出
1.
0x4006e8
2.
0x4006f8
3.
0x400700
4.
0x400708
[root@localhostzz]#objdump-d a.out
a、 输出：文件格式elf64-LITLEARCH64
分解.init节：
0000000000400408 :
400408:a9bf7bfd stp x29，x30，[sp，#-16]！
40040c:910003fd mov x29，sp
400410:94000032 bl 4004d8
400414:a8c17bfd ldp x29，x30，[sp]，#16
400418:d65f03c0 ret
节段plt的拆卸：
0000000000400420 :
400420:a9bf7bf0 stp x16，x30，[sp，#-16]！
400424:f00000f0 adrp X1641F000
400428:f947fe11 ldr x17[x16，#4088]
40042c:913fe210添加x16、x16、#0xff8
400430:d61f0220 br x17
400434:d503201f nop
400438:d503201f nop
40043c:d503201f nop
0000000000400440 :
400440:9000010 adrp X16420000
400444:f9400211 ldr x17[x16]
400448:91000210添加x16、x16、#0x0
40044c:d61f0220 br x17
0000000000400450 :
400450:9000010 adrp X16420000
400454:f9400611 ldr x17[x16，#8]
400458:91002210添加x16、x16、#0x8
40045c:d61f0220 br x17
0000000000400460 :
400460:9000010 adrp X16420000
400464:f9400a11 ldr x17，[x16，#16]
400468:91004210添加x16、x16、#0x10
40046c:d61f0220 br x17
0000000000400470 :
400470:9000010 adrp X16420000
400474:f9400e11 ldr x17，[x16，#24]
400478:91006210添加x16、x16、#0x18
40047c:d61f0220 br x17
0000000000400480 :
400480:9000010 adrp X16420000
400484:f9401211 ldr x17[x16，#32]
400488:91008210添加x16、x16、#0x20
40048c:d61f0220 br x17
第节的分解。正文：
0000000000400490 :
400490:d280001d mov x29，#0x0/#0
400494:d280001e mov x30，#0x0/#0
400498:910003fd mov x29，sp
40049c:aa0003e5 mov x5，x0
4004a0:f94003e1 ldr x1[sp]
4004a4:910023e2添加x2，sp，#0x8
4004a8:910003e6 mov x6，sp
4004ac:580000a0 ldr x0，4004c0
4004b0:580000c3 ldr x3，4004c8
4004b4:580000e4 ldr X44004D0
4004b8:97FFFF2 bl 400440
公元前4004bc:97FFFF9 bl 400460
4004c0:00400594.字0x00400594
4004c4:00000000。字0x00000000
4004c8:00400638.字0x00400638
4004cc:00000000。字0x00000000
4004d0:004006b8.字0x004006b8
4004d4:00000000。字0x00000000
0000000000 4004D8：
4004d8:f00000e0 adrp x0，41f000
4004dc:f947f000 ldr x0，[x0，#4064]
4004e0:b4000040 cbz x0，4004e8
4004e4:17ffffdb b 400450
4004e8:d65f03c0 ret
4004ec:00000000。指令0x00000000；未定义
0000000000 4004F0：
4004f0:90000100 adrp X420000
4004f4:9100e000加上x0，x0，#0x38
4004f8:90000101 adrp x1，420000
4004fc:9100e021添加x1，x1，#0x38
400500:eb00003f cmp x1，x0
400504:540000a0 b.eq 400518
400508:90000001 adrp x1，400000
40050c:f9436c21 ldr x1[x1，#1752]
400510:b4000041 cbz x1，400518
400514:d61f0020 br x1
400518:d65f03c0 ret
40051c:d503201f编号
0000000000400520 :
400520:90000100 adrp X420000
400524:9100e000加上x0，x0，#0x38
400528:90000101 adrp x1，420000
40052c:9100e021添加x1，x1，#0x38
400530:cb000021子x1、x1、x0
400534:9343fc21 asr x1，x1，#3
400538:8b41fc21添加x1、x1、x1、lsr#63
40053c:9341fc21 asr x1，