Databases
StackOverflow2013
Postsdbo
POglibc detected invalid pointer
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POglibc detected invalid pointer
    primarykey
    data
    text
    <p>So for one of my school assignments I have to implement my own memory allocation package. I use a struct block that represents a free block of memory and create a list of those blocks showing where the free spaces on my memory heap are, also known as my 'free list'. Below is the block struct I create.</p> <pre><code> typedef struct block { struct block *next; struct block *prev; int size; unsigned char *buffer; } block; </code></pre> <p>my_malloc() implementation (see below) seems to be working fine under my tests. </p> <pre><code>void *my_malloc(int size){ //if my_malloc has never been called before create the first // free block who's data buffer spans the entire heap if(!initialized){ initialized = 1; //Next time, we've already inited // Create the first block *(block *)head = (block){NULL, NULL, 0, NULL}; block *p = (block *)head; //try setting size to 128KB and point buffer properly p-&gt;size = 1024*128; p-&gt;buffer = p+ 1; printf("Address of buffer is %p\n", p-&gt;buffer); // set the program break brk(head + (sizeof(block)+p-&gt;size)); } block *p = (block *)head; //point to the head, we don't want to move the head... // find the appropriate free block and check for nullity block *selected = find_block(size); if(selected==NULL){ printf("Had no space first time around!\n"); //go to the end of the free list while(p-&gt;next!=NULL){ p=p-&gt;next; } // increase it's size by 128KB p-&gt;size=p-&gt;size+(128*1024); // move the program break by additional 128KB sbrk(128*1024); //now the last free block has enough space, so make it the selected block selected=p; } block *new_block; // new block we will create // if the block we have to allocate is pointed by head, we need a new // head if ((block *)selected==(block *)head){ //shift head head = selected-&gt;buffer+ size; //Create a new block there, it wil be our new head and we don't return it *(block *)head = (block){NULL, NULL, 0, NULL}; block *new_block = (block *)head; new_block-&gt;prev = selected-&gt;prev; new_block-&gt;next = selected-&gt;next; new_block-&gt;size = selected-&gt;size-size; new_block-&gt;buffer = new_block +1; printf("The split new_block-&gt;buffer points to %p\n", new_block-&gt;buffer); //return the pointer to original head, not the new one. total_malloced=+size; return selected-&gt;buffer; } // The selected node is not the head so we don't move the head else{ new_block = selected-&gt;buffer+size; new_block-&gt;prev = selected-&gt;prev; new_block-&gt;next = selected-&gt;next; new_block-&gt;size = selected-&gt;size-size; new_block-&gt;buffer = new_block +1; //remove that selected block from the free list (selected-&gt;prev)-&gt;next=new_block; total_malloced=+size; return selected-&gt;buffer; } } </code></pre> <p>The issue occurs when sending the returned pointer of my_malloc to a method like my_free().</p> <pre><code>void my_free(void *ptr) { printf("Dummy instruct.\n"); } </code></pre> <p>I get the following error:</p> <pre><code>*** glibc detected *** ./myMalloc: munmap_chunk(): invalid pointer: 0x0804a17e *** ======= Backtrace: ========= /lib/i386-linux-gnu/libc.so.6(+0x75ee2)[0xb7e7cee2] /lib/i386-linux-gnu/libc.so.6(+0x765c5)[0xb7e7d5c5] ./myMalloc[0x80485b1] /lib/i386-linux-gnu/libc.so.6(__libc_start_main+0xf3)[0xb7e204d3] ./myMalloc[0x8048401] ======= Memory map: ======== 08048000-08049000 r-xp 00000000 00:3d 8557227 /home/2009/gkrink/os/myMalloc 08049000-0804a000 r--p 00000000 00:3d 8557227 /home/2009/gkrink/os/myMalloc 0804a000-0804b000 rw-p 00001000 00:3d 8557227 /home/2009/gkrink/os/myMalloc 0804b000-0808c000 rw-p 00000000 00:00 0 [heap] b7e06000-b7e07000 rw-p 00000000 00:00 0 b7e07000-b7faa000 r-xp 00000000 00:11 4370765 /lib/i386-linux-gnu/libc-2.15.so b7faa000-b7fab000 ---p 001a3000 00:11 4370765 /lib/i386-linux-gnu/libc-2.15.so b7fab000-b7fad000 r--p 001a3000 00:11 4370765 /lib/i386-linux-gnu/libc-2.15.so b7fad000-b7fae000 rw-p 001a5000 00:11 4370765 /lib/i386-linux-gnu/libc-2.15.so b7fae000-b7fb1000 rw-p 00000000 00:00 0 b7fbb000-b7fd7000 r-xp 00000000 00:11 6829467 /lib/i386-linux-gnu/libgcc_s.so.1 b7fd7000-b7fd8000 r--p 0001b000 00:11 6829467 /lib/i386-linux-gnu/libgcc_s.so.1 b7fd8000-b7fd9000 rw-p 0001c000 00:11 6829467 /lib/i386-linux-gnu/libgcc_s.so.1 b7fd9000-b7fdd000 rw-p 00000000 00:00 0 b7fdd000-b7fde000 r-xp 00000000 00:00 0 [vdso] b7fde000-b7ffe000 r-xp 00000000 00:11 4370778 /lib/i386-linux-gnu/ld-2.15.so b7ffe000-b7fff000 r--p 0001f000 00:11 4370778 /lib/i386-linux-gnu/ld-2.15.so b7fff000-b8000000 rw-p 00020000 00:11 4370778 /lib/i386-linux-gnu/ld-2.15.so bffdf000-c0000000 rw-p 00000000 00:00 0 [stack] Aborted </code></pre> <p>And here is my test function:</p> <pre><code>void main(void){ printf("Testing initiated...\n"); printf("head is located at %p\n\n", head); void * tester; printf("mallocing 100...\n"); tester = my_malloc(100); printf("The allocated memory starts at %p\n", tester); printf("mallocing 150...\n"); tester=my_malloc(150); printf("The allocated memory starts at %p\n", tester); printf("head is located at %p\n\n", head); printf("brk is firstly located at %p\n", sbrk(0)); printf("mallocing 10..."); tester=my_malloc(10); printf("The allocated memory starts at %p\n", tester); printf("brk is still at %p\n", sbrk(0)); free(tester); } </code></pre> <p>And without sending the returned pointer of my_malloc() to my_free() I get correct output such as:</p> <blockquote> <p>Testing initiated... head is located at 0x804a054</p> <p>mallocing 100... Address of buffer is 0x804a064 The split new_block->buffer points to 0x804a0d8 The allocated memory starts at 0x804a064 mallocing 150... The split new_block->buffer points to 0x804a17e The allocated memory starts at 0x804a0d8 head is located at 0x804a16e</p> <p>brk is firstly located at 0x806a064 mallocing 10...The split new_block->buffer points to 0x804a198 The allocated memory starts at 0x804a17e brk is still at 0x806a064</p> </blockquote> <p>Why can't I send pointers to another function like that?</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. This table or related slice is empty.
    1. USGeorges Krinker
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POglibc detected invalid pointer
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POglibc detected invalid pointer
      1. This table or related slice is empty.
      1. VTClose
    3. VO
      singulars
      1. POglibc detected invalid pointer
      1. USAdri C.S.
      1. VTFavorite
    1. This table or related slice is empty.
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload