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# Project 2
### 組員名單
* 110525015 劉松靄
* 111525013 何雋永
* 109502547 楊晴方
### 系統環境
* 作業系統： ubuntu 18.04
* Kernel 版本： 5.4.0-131-generic
### 新增 syscall 過程
由於篇幅較多，因此另外寫了一篇，在[這裡](https://hackmd.io/7x2suD5FRPuoavelhqUP4Q)。
### Project 1
有些補充的知識點在 project 1，所以在此留個[傳送門](https://hackmd.io/4SgqE4UARS-VcxfUWyLSjA?both)。
### kernel space code
```
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/mm.h>
#include <linux/syscalls.h>
#include <linux/uaccess.h>
int segNum = 6;
int *data[20];
char* segmentName[6] = {"BSS", "Text", "Data", "Heap", "Stack", "Shared library"};
void printVMA(struct task_struct *task){
struct mm_struct *mm = task->mm;
struct vm_area_struct *vma;
int count = 0, index = 0;
printk("\nText Segment start = 0x%lx, end = 0x%lx\n"
"\nData Segment start = 0x%lx, end = 0x%lx\n"
"\nStack Segment start = 0x%lx\n"
"\nHeap Segment start = 0x%lx, end = 0x%lx\n",
mm->start_code, mm->end_code,
mm->start_data, mm->end_data,
mm->start_stack,
mm->start_brk, mm->brk);
for(; index < segNum; index++){
count = 0;
for(vma = mm->mmap; vma; vma = vma->vm_next){
++count;
if(data[index] >= vma->vm_start && data[index] <= vma->vm_end){
printk("\n%s Segment is in vma %d\n", segmentName[index], count);
printk("\nStarts at 0x%lx, Ends at 0x%lx\n", vma->vm_start, vma->vm_end);
}
}
}
}
void convertToPhysical(struct task_struct *task){
pgd_t *pgd;
p4d_t *p4d;
pud_t *pud;
pmd_t *pmd;
pte_t *pte;
unsigned long paddr=0, page_addr=0, page_offset=0;
int index=0;
for(; index<segNum; index++){
pgd = pgd_offset(task->mm, data[index]);
if(pgd_none(*pgd)){
printk("not mapped in pgd\n");
return;
}
p4d = p4d_offset(pgd, data[index]);
if(p4d_none(*p4d)){
printk("not mapped in p4d\n");
return;
}
pud = pud_offset(p4d, data[index]);
if(pud_none(*pud)){
printk("not mapped in pud\n");
return;
}
pmd = pmd_offset(pud, data[index]);
if(pmd_none(*pmd)){
printk("not mapped in pmd\n");
return;
}
pte = pte_offset_kernel(pmd, data[index]);
if(pte_none(*pte)){
printk("not mapped in pte\n");
return;
}
page_addr = pte_val(*pte) & PAGE_MASK;
page_offset = (unsigned long)data[index] & ~PAGE_MASK;
paddr = page_addr | page_offset;
printk("\nphysical address %s Segment is 0x%lx\n", segmentName[index], paddr);
}
}
SYSCALL_DEFINE2(printSegment, int, pid, const int*, userData){
copy_from_user(data, userData, sizeof(data));
printk("\ntask id is %d\n", current->pid);
convertToPhysical(current);
printVMA(current);
return 0;
}
```
### user space code
```
#include <stdio.h>
#include <unistd.h>
#include <sys/syscall.h>
#include <linux/kernel.h>
int initData = 1, cnt = 0;
int notInitData;
int *userData[20] = {0};
int main(){
int a = 1;
int *p = malloc(sizeof(int));
printf("%d\n", initData);
userData[cnt++] = ¬InitData;
userData[cnt++] = main;
userData[cnt++] = &initData;
userData[cnt++] = p;
userData[cnt++] = &a;
userData[cnt++] = printf;
syscall(336, (int)syscall(SYS_gettid), userData);
sleep(5);
return 0;
}
```
### kernel 輸出結果
```
[278649.368720]
task id is 31499
[278649.368730]
physical address BSS Segment is 0x800000021d832100
[278649.368736]
physical address Text Segment is 0x206e6f77a
[278649.368739]
physical address Data Segment is 0x800000021d832010
[278649.368742]
physical address Heap Segment is 0x800000025b9a9260
[278649.368745]
physical address Stack Segment is 0x800000020cebe39c
[278649.368747]
physical address Shared library Segment is 0x110d3de40
[278649.368750]
Text Segment start = 0x557d93c00000, end = 0x557d93c00ae0
Data Segment start = 0x557d93e00d98, end = 0x557d93e01014
Stack Segment start = 0x7ffef193f490
Heap Segment start = 0x557d94df7000, end = 0x557d94e18000
[278649.368758]
BSS Segment is in vma 3
[278649.368761]
Starts at 0x557d93e01000, Ends at 0x557d93e02000
[278649.368765]
Text Segment is in vma 1
[278649.368767]
Starts at 0x557d93c00000, Ends at 0x557d93c01000
[278649.368770]
Data Segment is in vma 3
[278649.368772]
Starts at 0x557d93e01000, Ends at 0x557d93e02000
[278649.368775]
Heap Segment is in vma 4
[278649.368777]
Starts at 0x557d94df7000, Ends at 0x557d94e18000
[278649.368780]
Stack Segment is in vma 15
[278649.368783]
Starts at 0x7ffef1920000, Ends at 0x7ffef1941000
[278649.368785]
Shared library Segment is in vma 5
[278649.368788]
Starts at 0x7f8ca4000000, Ends at 0x7f8ca41e7000
[278651.842351]
task id is 31500
[278651.842361]
physical address BSS Segment is 0x800000024909c100
[278651.842367]
physical address Text Segment is 0x206e6f77a
[278651.842370]
physical address Data Segment is 0x800000024909c010
[278651.842373]
physical address Heap Segment is 0x800000023360d260
[278651.842375]
physical address Stack Segment is 0x8000000247e2f3dc
[278651.842378]
physical address Shared library Segment is 0x110d3de40
[278651.842381]
Text Segment start = 0x55b30fc00000, end = 0x55b30fc00ae0
Data Segment start = 0x55b30fe00d98, end = 0x55b30fe01014
Stack Segment start = 0x7ffe2b4e84d0
Heap Segment start = 0x55b311557000, end = 0x55b311578000
[278651.842389]
BSS Segment is in vma 3
[278651.842392]
Starts at 0x55b30fe01000, Ends at 0x55b30fe02000
[278651.842395]
Text Segment is in vma 1
[278651.842398]
Starts at 0x55b30fc00000, Ends at 0x55b30fc01000
[278651.842401]
Data Segment is in vma 3
[278651.842403]
Starts at 0x55b30fe01000, Ends at 0x55b30fe02000
[278651.842405]
Heap Segment is in vma 4
[278651.842408]
Starts at 0x55b311557000, Ends at 0x55b311578000
[278651.842410]
Stack Segment is in vma 15
[278651.842413]
Starts at 0x7ffe2b4c9000, Ends at 0x7ffe2b4ea000
[278651.842416]
Shared library Segment is in vma 5
[278651.842419]
Starts at 0x7f3ba5800000, Ends at 0x7f3ba59e7000
```
### 結論
從上圖的輸出結果可觀察到在兩個 process 中 Text、Shared library 這兩個 segment 的 physical address 都相同，所以它們是共用的。
### Reference
[https://www.jianshu.com/p/0520d6b76318](https://www.jianshu.com/p/0520d6b76318)
[https://kkc.github.io/2020/08/22/file-descriptor/](https://kkc.github.io/2020/08/22/file-descriptor/)
[https://stackoverflow.com/questions/32170711/how-is-the-code-segment-shared-between-processes-in-linux](https://stackoverflow.com/questions/32170711/how-is-the-code-segment-shared-between-processes-in-linux)
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