Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p><code>esp</code> is as you say it is, the top of the stack.</p> <p><code>ebp</code> is usually set to <code>esp</code> at the start of the function. Function parameters and local variables are accessed by adding and subtracting, respectively, a constant offset from <code>ebp</code>. All x86 calling conventions define <code>ebp</code> as being preserved across function calls. <code>ebp</code> itself actually points to the previous frame's base pointer, which enables stack walking in a debugger and viewing other frames local variables to work. </p> <p>Most function prologs look something like:</p> <pre class="lang-none prettyprint-override"><code>push ebp ; Preserve current frame pointer mov ebp, esp ; Create new frame pointer pointing to current stack top sub esp, 20 ; allocate 20 bytes worth of locals on stack. </code></pre> <p>Then later in the function you may have code like (presuming both local variables are 4 bytes)</p> <pre class="lang-none prettyprint-override"><code>mov [ebp-4], eax ; Store eax in first local mov ebx, [ebp - 8] ; Load ebx from second local </code></pre> <p>FPO or <em>frame pointer omission</em> optimization which you can enable will actually eliminate this and use <code>ebp</code> as another register and access locals directly off of <code>esp</code>, but this makes debugging a bit more difficult since the debugger can no longer directly access the stack frames of earlier function calls.</p> <p>EDIT:</p> <p>For your updated question, the missing two entries in the stack are:</p> <pre class="lang-none prettyprint-override"><code>var_C = dword ptr -0Ch var_8 = dword ptr -8 var_4 = dword ptr -4 *savedFramePointer = dword ptr 0* *return address = dword ptr 4* hInstance = dword ptr 8h PrevInstance = dword ptr 0C hlpCmdLine = dword ptr 10h nShowCmd = dword ptr 14h </code></pre> <p>This is because the flow of the function call is:</p> <ul> <li>Push parameters (<code>hInstance</code>, etc.)</li> <li>Call function, which pushes return address</li> <li>Push <code>ebp</code></li> <li>Allocate space for locals</li> </ul>
    singulars
    1. This table or related slice is empty.
    1. POWhat is exactly the base pointer and stack pointer? To what do they point?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. This table or related slice is empty.
    1. USMichael
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POWhat is exactly the base pointer and stack pointer? To what do they point?
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. CO+1 and would do another one if possible. Nice and comprehensive explanation!
      singulars
      1. PO
      1. USmmmmmmmm
    2. COThanks for the explanation! But I am now kinda confused. Let's assume I call a function and I am in the first line of its prolog, still without having executed a single line from it. At that point, what is ebp's value? Does the stack have anything at that point besides the pushed arguments? Thanks!
      singulars
      1. PO
      1. USdevoured elysium
    3. COEBP is not magically changed, so until you've established a new EBP for your function you'll still have the callers value. And besides arguments, the stack will also hold the old EIP (return address)
      singulars
      1. PO
      1. USMSalters
 

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