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ideas of memory pool

· One min read

the key information to implement a memory pool​

  • boundary:

How to solve the boundaries between different different chunks

  • name:

How to get an allocated memory chunk

  • reference count

whether the chunk is still used. I want to free the memory only if the process termination or free, with threads free, only do reference count minus 1.

  • data structure:

which data structure will be efficient?

memory leak

· One min read

find memory leak of a running process​

$ cat /proc/$pid/smaps
  1. find out the PID of the process
$ ps -aux
  1. capture /proc/PID/smaps and save into some file like before_meminc.txt
  2. wait till memory gets increased
  3. try again step 2
  4. find the difference between first smaps and 2nd smaps, e.g. with
$ diff -u before_meminc.txt after_meminc.txt

  1. note down the address range where memory got increased

  2. use pstack and watch command to get the right call stack

$ watch -n 1 'pstack $PID | tee -a $PID.stack'

C-c when we caputred right stack

  1. check our stack file, find the functions between address range which we got from step 6.

gcc error when inline without static

· 3 min read

gcc error when inline without static​

inline only​

C code:​

#include <stdio.h>

inline int func() { printf("dll\n"); }

int main() { func(); }

asm code:​

  .section	__TEXT,__text,regular,pure_instructions
  .build_version macos, 11, 0	sdk_version 11, 1
  .globl	_main                   ## -- Begin function main
  .p2align	4, 0x90
_main:                                  ## @main
  .cfi_startproc
## %bb.0:
  pushq	%rbp
  .cfi_def_cfa_offset 16
  .cfi_offset %rbp, -16
  movq	%rsp, %rbp
  .cfi_def_cfa_register %rbp
  subq	$16, %rsp
  callq	_func
  xorl	%ecx, %ecx
  movl	%eax, -4(%rbp)          ## 4-byte Spill
  movl	%ecx, %eax
  addq	$16, %rsp
  popq	%rbp
  retq
  .cfi_endproc
                                        ## -- End function
.subsections_via_symbols

With static​

C code​

#include <stdio.h>

static inline int func() { printf("dll\n"); }

int main() { func(); }

asm code​

  .section	__TEXT,__text,regular,pure_instructions
  .build_version macos, 11, 0	sdk_version 11, 1
  .globl	_main                   ## -- Begin function main
  .p2align	4, 0x90
_main:                                  ## @main
  .cfi_startproc
## %bb.0:
  pushq	%rbp
  .cfi_def_cfa_offset 16
  .cfi_offset %rbp, -16
  movq	%rsp, %rbp
  .cfi_def_cfa_register %rbp
  subq	$16, %rsp
  callq	_func
  xorl	%ecx, %ecx
  movl	%eax, -4(%rbp)          ## 4-byte Spill
  movl	%ecx, %eax
  addq	$16, %rsp
  popq	%rbp
  retq
  .cfi_endproc
                                        ## -- End function
  .p2align	4, 0x90         ## -- Begin function func
_func:                                  ## @func
  .cfi_startproc
## %bb.0:
  pushq	%rbp
  .cfi_def_cfa_offset 16
  .cfi_offset %rbp, -16
  movq	%rsp, %rbp
  .cfi_def_cfa_register %rbp
  subq	$16, %rsp
  leaq	L_.str(%rip), %rdi
  movb	$0, %al
  callq	_printf
  movl	-4(%rbp), %ecx
  movl	%eax, -8(%rbp)          ## 4-byte Spill
  movl	%ecx, %eax
  addq	$16, %rsp
  popq	%rbp
  retq
  .cfi_endproc
                                        ## -- End function
  .section	__TEXT,__cstring,cstring_literals
L_.str:                                 ## @.str
  .asciz	"dll\n"

.subsections_via_symbols

With __attribute__​

C code​

#include <stdio.h>

#define inline __attribute__((alwyas_inline))

inline int func() { printf("dll\n"); }

int main() { func(); }

asm code​

  .section	__TEXT,__text,regular,pure_instructions
  .build_version macos, 11, 0	sdk_version 11, 1
  .globl	_func                   ## -- Begin function func
  .p2align	4, 0x90
_func:                                  ## @func
  .cfi_startproc
## %bb.0:
  pushq	%rbp
  .cfi_def_cfa_offset 16
  .cfi_offset %rbp, -16
  movq	%rsp, %rbp
  .cfi_def_cfa_register %rbp
  subq	$16, %rsp
  leaq	L_.str(%rip), %rdi
  movb	$0, %al
  callq	_printf
  movl	-4(%rbp), %ecx
  movl	%eax, -8(%rbp)          ## 4-byte Spill
  movl	%ecx, %eax
  addq	$16, %rsp
  popq	%rbp
  retq
  .cfi_endproc
                                        ## -- End function
  .globl	_main                   ## -- Begin function main
  .p2align	4, 0x90
_main:                                  ## @main
  .cfi_startproc
## %bb.0:
  pushq	%rbp
  .cfi_def_cfa_offset 16
  .cfi_offset %rbp, -16
  movq	%rsp, %rbp
  .cfi_def_cfa_register %rbp
  subq	$16, %rsp
  callq	_func
  xorl	%ecx, %ecx
  movl	%eax, -4(%rbp)          ## 4-byte Spill
  movl	%ecx, %eax
  addq	$16, %rsp
  popq	%rbp
  retq
  .cfi_endproc
                                        ## -- End function
  .section	__TEXT,__cstring,cstring_literals
L_.str:                                 ## @.str
  .asciz	"dll\n"

.subsections_via_symbols

center tables in a markdown file

· One min read

center tables in a markdown file​

<div align="center">

| Descriptoion                 | struct passwd member | POSIX.1   | FreeBSD 8.0 | Linux 32.0 | Mac OS X 10.6.8 | Solaris   |
|:-----------------------------|:---------------------|:---------:|:-----------:|:----------:|:---------------:|:---------:|
| user name                    | char  *pw_name       | $\bullet$ | $\bullet$   | $\bullet$  | $\bullet$       | $\bullet$ |

_Figure 6.1 Fields in `/etc/passwd` file_
</div>

latex (math) support for markdown

· One min read

Math Equations​

  • import tha plugins in docusaurus.config.js
const math = require('remark-math');
const katex = require('rehype-katex');
remarkPlugins: [math],
rehypePlugins: [katex],

under stylesheets

stylesheets: [
  {
    href: 'https://cdn.jsdelivr.net/npm/katex@0.13.24/dist/katex.min.css',
    type: 'text/css',
    integrity:
      'sha384-odtC+0UGzzFL/6PNoE8rX/SPcQDXBJ+uRepguP4QkPCm2LBxH3FA3y+fKSiJ+AmM',
    crossorigin: 'anonymous',
  },
],
  • install modules
$ npm install --save remark-math@3 rehype-katex@5 hast-util-is-element@1.1.0