sd:code_gremlins
Differences
This shows you the differences between two versions of the page.
| Next revision | Previous revision | ||
| sd:code_gremlins [2026/01/29 01:43] – created - external edit 127.0.0.1 | sd:code_gremlins [2026/04/01 04:17] (current) – appledog | ||
|---|---|---|---|
| Line 49: | Line 49: | ||
| //" | //" | ||
| - | There are two forms of this goblin. They look exactly the same except one of them has a beard and a red hat, while all the other goblins have white hats. These goblins are relentless, they are constantly trying to fuck with the stack. | + | There are two forms of this goblin. They look exactly the same except one of them has a beard and a red hat, while all the other goblins have white hats. These goblins are relentless, |
| The first one looks for functions with unbalanced PUSH/POP. Returns to address $292929. Endless calls to LDA #0000. Corrupts everything in its wake. | The first one looks for functions with unbalanced PUSH/POP. Returns to address $292929. Endless calls to LDA #0000. Corrupts everything in its wake. | ||
| Line 70: | Line 70: | ||
| Weakness: His true name. You must call him by his true name: The carry gremlin. Call him by his name and, his true form revealed, he will disappear in a puff of smoke. | Weakness: His true name. You must call him by his true name: The carry gremlin. Call him by his name and, his true form revealed, he will disappear in a puff of smoke. | ||
| + | |||
| + | === Zero gremlins | ||
| + | This is really a goblin, but it is wearing a mask. Remove the mask and you see.. a goblin! Hes gobblin your CPU time. But wait.. he's wearing another mask! Remove the mask and what do you find? | ||
| + | |||
| + | NOP | ||
| + | |||
| + | Great scott! We're being invaded by NOPs! | ||
| + | |||
| + | To get rid of this Goblin, remember which ops set cpu flags. Before you flagrantly issue a CMP against zero, ask yourself; is it already set? | ||
| + | |||
| + | Here is the magic scroll to find and eradicate these gremlins; but beware, they are wearing masks, you must thoroughly investigate each case. | ||
| + | |||
| + | [^;]CMP [A-Za-z]+, | ||
| + | |||
| + | or maybe | ||
| + | |||
| + | ^\s+(LD|ADD|SUB|AND|OR|XOR|SHR|SHL|INC|DEC|MOV)\w*.*\n\s+CMP\s+[A-Za-z]+, | ||
| + | |||
| + | Surefire cases look like this: | ||
| + | |||
| + | LDA [$C000] | ||
| + | CMP A, #0 | ||
| + | JZ @label | ||
| + | |||
| + | Here, the CMP is always redundant as LD sets Z. Other common ops that set Z; ST, AND, DIV, MOV, INC, DEC... | ||
| + | |||
| + | === Zero gremlins II: The Revenge | ||
| + | The Zero gremlin never really went away, he just changed masks. | ||
| + | |||
| + | ^\s+(LD|ST)\w+.*\n\s+(INC|DEC)\s+ | ||
| + | ^\s+(INC|DEC)\s+.*\n\s+(LD|ST)\w+ | ||
| + | |||
| + | The above will unmask these goblins right away! | ||
| == History | == History | ||
sd/code_gremlins.1769650981.txt.gz · Last modified: by 127.0.0.1