57 lines
1.2 KiB
Markdown
57 lines
1.2 KiB
Markdown
# amd64
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* `rax` return value, caller saved.
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* `rbx` base register (used for mem basepointer)
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* `rcx` counter register
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* `r10`, `r11` are caller saved.
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* `rbx`, `r12`, `r13`, `r14` are callee saved
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* `rdx` data register
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* `rbp` is also callee saved(and can be optionally used as a frame pointer)
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* `rsp` is callee saved
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* `rip` next instruction pointer
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## Function argument registers
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* `rdi`,`rsi`,`rdx`,`rcx`,`r8 `,`r9 `, called saved.
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* Further function args are stored inside its stack frame.
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## Overwriting Variables and Padding
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* Overwrite an atomic variable behind a buffer
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```C
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int main ( int argc, char ** argv ) {
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int var = 0
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char buffer[12];
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gets(buffer);
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[...]
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}
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```
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* Stack layout
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```
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Bottom
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+------------------+
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| Saved registers |
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+------------------+
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| int var |
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+------------------+
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| char buffer [11] |
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| ... |
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| ... |
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| ... |
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| char buffer [0] |
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+------------------+
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| char ** argv |
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+------------------+
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| char argc |
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+------------------+
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Top
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```
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* Watch out! I.e., a 12 byte array is padded to system memory allocation size.
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```
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+-------------+----+
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|12 byte array| 4b |
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+-------------+----+
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0 12 16 byte
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```
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