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I am new to assembly level coding so I am bit confused what .align does. I have looked up what it does in many places.https://www.cl.cam.ac.uk/projects/raspberrypi/tutorials/os/ok05.html in this link a description on .align is given in red box on the right hand side of the page. Another place i refereed was http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dui0489c/Babecdje.html. What does it mean for a address to be 4 bytes aligned or 8 bytes aligned ?
If I use the following instructions in my code
.align 4
pattern:
Then does mean the address assigned to pattern will be of the form 4*n or 16*n ( 2^4 = 16).
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The ALIGN directive aligns the current location to a specified boundary by padding with zeros or NOP instructions.
ALIGN [[number]] Aligns the next variable or instruction on a byte that is a multiple of number. This is often used to optimize struct placement in memory, since all new x86 architectures have a word length over 8 bits (usually 32 or 64 bits).
The . ALIGN directive is a way to override the default alignment rules. The next field after the directive will be aligned to a multiple of 2 to the power of n where n is the . ALIGN value.
The ARM compiler normally aligns variables and pads structures so that these items are accessed efficiently using LDR and STR instructions. Known but non-natural alignment, for example, a word at address 0x1001. This type of alignment commonly occurs when structures are packed to remove unnecessary padding.
Data alignment basically depends upon the factors like address lines, data lines and number of physical divisions of memory device. Talking about ARMs, data alignment plays a pivotal role in the execution process. This has been explained in following points. ARMs have 32 address lines (A0 to A31). It has 32 data lines (D0 to D31).
ARM is an acronym for Advanced RISC Machine, but its original name was Acorn RISC machine developed by Arm Holdings, and this architecture was licensed to the third-party developer to package this in their products. 6502 based BBC Micro series was the first ARM product to be released. It did not support a graphic interface. 1.
Therefore, if data is properly aligned in the memory device then the time taken for the execution of the task is reduced to a great extent. Data alignment basically depends upon the factors like address lines, data lines and number of physical divisions of memory device.
ARM (stylised in lowercase as arm, formerly an acronym for Advanced RISC Machines and originally Acorn RISC Machine) is a family of reduced instruction set computer (RISC) instruction set architectures for computer processors, configured for various environments.
An address is said to be "n-bytes aligned" if it's evenly divisible by n.
This can also be expressed as "an address is 2m-bytes aligned if its rightmost m bits are all zero".
Alignment is very common a requirement, i.e. the hardware requires as part of its programming model that certain alignment requirements are always respected. Failure to do so might lead to a hard fault, i.e. the processor stops.
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