Description:
Bulletin Board and Q&A for x86 assembly language topics. (Moderated)
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Question about stack...
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So I'm reserving room on the stack for a local variable, I'm in 16-bit assembly and I decide to reserve room for a 16-bit word, so I subtract 2 from sp. SUB SP, 2 MOV BP, SP MOV word [BP], myvalue In this case it wasn't overwritten. When I didn't adjust the value of SP and did: MOV BP, SP MOV WORD [BP-2], myvalue... more »
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OK to use MMX registers as temporary storage?
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Hi all, I'm coding a routine and I'm using all of the registers. I need to do a division which means I am going to have to free up EAX and EDX. Is it possible for me to simply MOVD them into the MMX registers without causing any problems? I am not doing any floating point math nor MMX operations in my routine.... more »
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Monitoring segment registers?
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Hi, I want to monitor all the activities of segment registers like CS, DS... inside a virtual machine. For ex, I want to get notified whenever CS or DS changes their values. I want to use some features of Intel VT to do this. I imagine that I can set some conditions so whenever these registers change values, it... more »
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implementing call stack
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Hi, Im working on a asm debugger. The source is a higher level programming language (VHDL), which is similar in some aspect to Pascal/C (the source may contain procedures). Now I can put breakpoints to the source VHDL code and the debugger stay correctly at a point in the x86 code. Im using runtime... more »
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Using labels as immediate operands in GAS with intel syntax
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I have the following code for a hello world program for GAS: .intel_syntax noprefix .data # section declaration msg: .ascii "Hello, world!\n" # our dear string len = . - msg # length of our dear string msg_p: .int msg len_p: .int len .text # section declaration # we must export the entry point to the ELF linker or... more »
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A valid number of prefixes
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Hey guys! I have this question related to instruction prefixes in ia-32/64. I did some work with software protections and code obfuscations. And I have seen instruction prefixes in many cases where their use is reserved, for example jmp instruction and rep prefix. So my question is, how many prefixes does the instruction can... more »
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problem while using inline assembly
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Hi, I am trying to use the inline assembly. int y; asm ("mov %fs:thread_local@TPOFF, %rax"); asm ("mov %%rax, %%rbx;" :"=Ab" (y) ); This code works perfectly fine. when i try to compile the following piece of code int y; 20 asm ("mov %fs:thread_local@TPOFF, %rax;"... more »
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Changing FPU rounding mode
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Hi, Problem: After I change the FPU rounding mode with the assembly instruction fldcw, the rounding mode is reset back to the default after the program finishes running. How can I make the change permanent (i.e.until the next time fldcw is called or machine reboot)? I wrote the following program to change the FPU rounding mode from the... more »
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Access PCI memory space from DOS real mode
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For some reason, my original post did not show up in this newsgroup. I am posting again. Hi All, I am working on an DOS network driver for a PCI Express NIC device. The device does not have I/O space but only memory bar. The issue is my driver is running under 16 bit real mode and how can the driver... more »
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