What changes have occurred to the register when calling the function?

There has always been a vague concept, so we use an example to strengthen memory.

Linux x86 gcc3.2.3 at&t format Compilation

The Code is as follows:

Void

Fun ()

{

Int A = 'a ';

}

Void

Main ()

{

Int B;

Fun ();

Return;

}

Start debugging

[Sanool @ sanool ex2] $ gdb a. Out

Gnu gdb Red Hat Linux (6.0post-0.20031117.6rh)

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This GDB was configured as "i386-redhat-linux-gnu"... (no debugging symbols found)... using host libthread_db library "/lib/tls/libthread_db.so.1 ".

(GDB) disas main

Dump of worker er code for function main:

0x08048323: Push % EBP

0x08048324: mov % ESP, % EBP

0x08048326: Sub $0x8, % ESP

0x08048329: and $0xfffffff0, % ESP

0x0804832c: mov $0x0, % eax

0x08048331: Sub % eax, % ESP

0x08048333: Call 0x8048314

Zero X 08048338: Leave

0x08048339: Ret

0x0804833a: NOP

0x0804833b: NOP

End of worker er dump.

(GDB) disas fun

Dump of javaser code for function fun:

0x08048314: Push % EBP

0x08048315: mov % ESP, % EBP

0x08048317: Sub $0x4, % ESP

0x0804831a: movl $0x41, 0 xfffffffc (% EBP)

Zero X 08048321: Leave

0x08048322: Ret

End of worker er dump.

Explanation:

** When the program executes 0x08048333: Call 0x8048314 next

ESP = 0xbfffe660 (runtime)

EBP = 0xbfffe668 (runtime)

EIP = 0x08048333

** Then execute call 0x8048314, that is

Push % EIP (equivalent to sub $ 4% ESP and mov % EIP % ESP)

Movl $0x8048314, % EIP

The value of 0xbfffe65c is EIP = 0x08048338.

And ESP = 0xbfffe65c

EIP = 0x8048314

EBP = 0xbfffe668

** Execute 0x08048314: Push % EBP

ESP = 0xbfffe658

EBP = 0xbfffe668

The value at 0xbfffe658 is EBP = 0xbfffe668.

** Continue with 0x08048315: mov % ESP, % EBP

Assign the value of ESP to EBP.

That is, EBP = ESP = 0xbfffe658

** Start to execute 0x08048321: Before leave

EIP = 0x08048321

EBP = 0xbfffe658

ESP = 0xbfffe654

** When 0x08048321: leave is started

That is

Movl % EBP, % ESP (I .e. ESP = EBP = 0xbfffe658)

Pop % EBP (that is, mov % ESP, % EBP and add $4, % ESP)

At this time, EBP = 0xbfffe668 returns to the EBP value of the original function,

** Execute 0x08048322: Ret again.

Pop % EIP

(That is, mov % ESP, % eip and then add $4, % ESP)

In this case, EIP = 0x08048338

Program continues to execute leave in main

Call the fun function.