No system call when malloc after free
Hello StackExchange community.
While I was playing a little with kernel audit system, I made a small C program:
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char** argv){
void *t;
while(1){
t = malloc(1);
free(t);
}
return 0;
}
And applied the following filters to audit:
-a always,exit -F arch=b32 -S open,openat -F exit=-EACCES -F key=access
-a always,exit -F arch=b64 -S open,openat -F exit=-EACCES -F key=access
-a always,exit -F arch=b32 -S brk
-a always,exit -F arch=b64 -S brk
After compiling and running, I noticed that sys_brk wasn't showing up in the audit log.
Furthermore it didn't also appear in strace, even tho malloc was called (checked with ltrace).
Lastly I removed the free and the calls to sys_brk started showing up.
My question is what is causing this type of behaviour? Does glibc make some kind of optimization in malloc and free functions to prevent useless syscalls?
Thank you for your time.
TL;DR: free followed by malloc makes neither call the kernel. Why?
linux linux-kernel linux-audit
asked 18 mins ago
Jorge HelenoJorge Heleno
1114
add a comment |
Hello StackExchange community.
While I was playing a little with kernel audit system, I made a small C program:
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char** argv){
void *t;
while(1){
t = malloc(1);
free(t);
}
return 0;
}
And applied the following filters to audit:
-a always,exit -F arch=b32 -S open,openat -F exit=-EACCES -F key=access
-a always,exit -F arch=b64 -S open,openat -F exit=-EACCES -F key=access
-a always,exit -F arch=b32 -S brk
-a always,exit -F arch=b64 -S brk
After compiling and running, I noticed that sys_brk wasn't showing up in the audit log.
Furthermore it didn't also appear in strace, even tho malloc was called (checked with ltrace).
Lastly I removed the free and the calls to sys_brk started showing up.
My question is what is causing this type of behaviour? Does glibc make some kind of optimization in malloc and free functions to prevent useless syscalls?
Thank you for your time.
TL;DR: free followed by malloc makes neither call the kernel. Why?
linux linux-kernel linux-audit
asked 18 mins ago
Jorge HelenoJorge Heleno
1114
It might use brk () or mmap ()
– 炸鱼薯条德里克
10 mins ago
add a comment |
Hello StackExchange community.
While I was playing a little with kernel audit system, I made a small C program:
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char** argv){
void *t;
while(1){
t = malloc(1);
free(t);
}
return 0;
}
And applied the following filters to audit:
-a always,exit -F arch=b32 -S open,openat -F exit=-EACCES -F key=access
-a always,exit -F arch=b64 -S open,openat -F exit=-EACCES -F key=access
-a always,exit -F arch=b32 -S brk
-a always,exit -F arch=b64 -S brk
After compiling and running, I noticed that sys_brk wasn't showing up in the audit log.
Furthermore it didn't also appear in strace, even tho malloc was called (checked with ltrace).
Lastly I removed the free and the calls to sys_brk started showing up.
My question is what is causing this type of behaviour? Does glibc make some kind of optimization in malloc and free functions to prevent useless syscalls?
Thank you for your time.
TL;DR: free followed by malloc makes neither call the kernel. Why?
linux linux-kernel linux-audit
asked 18 mins ago
Jorge HelenoJorge Heleno
1114
Hello StackExchange community.
While I was playing a little with kernel audit system, I made a small C program:
#include <stdio.h>
#include <stdlib.h>
int main(int argc, char** argv){
void *t;
while(1){
t = malloc(1);
free(t);
}
return 0;
}
And applied the following filters to audit:
-a always,exit -F arch=b32 -S open,openat -F exit=-EACCES -F key=access
-a always,exit -F arch=b64 -S open,openat -F exit=-EACCES -F key=access
-a always,exit -F arch=b32 -S brk
-a always,exit -F arch=b64 -S brk
After compiling and running, I noticed that sys_brk wasn't showing up in the audit log.
Furthermore it didn't also appear in strace, even tho malloc was called (checked with ltrace).
Lastly I removed the free and the calls to sys_brk started showing up.
My question is what is causing this type of behaviour? Does glibc make some kind of optimization in malloc and free functions to prevent useless syscalls?
Thank you for your time.
TL;DR: free followed by malloc makes neither call the kernel. Why?
linux linux-kernel linux-audit
linux linux-kernel linux-audit
asked 18 mins ago
Jorge HelenoJorge Heleno
1114
asked 18 mins ago
Jorge HelenoJorge Heleno
1114
asked 18 mins ago
Jorge HelenoJorge Heleno
1114
asked 18 mins ago
Jorge HelenoJorge Heleno
1114
asked 18 mins ago
Jorge HelenoJorge Heleno
1114
1114
It might use brk () or mmap ()
– 炸鱼薯条德里克
10 mins ago
add a comment |
It might use brk () or mmap ()
– 炸鱼薯条德里克
10 mins ago
It might use brk () or mmap ()
– 炸鱼薯条德里克
10 mins ago
It might use brk () or mmap ()
– 炸鱼薯条德里克
10 mins ago
add a comment |
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It might use brk () or mmap ()
– 炸鱼薯条德里克
10 mins ago