thumb

under "The Thumb instruction set" in section 1-34 of "ARM11TechnicalRefManual" it said that: "The Thumb instruction set is a subset of the most commonly used 32-bit ARM instructions.Thumb instructions are 16 bits long,and have a corresponding 32-bit ARM instruction that has the same effect on processor model." can any one explain more about this especially second sentence and say how does processor perform it? The ARM processor has 2 instruction sets, the traditional ARM set, where the instructions are all 32-bit long, and the more condensed Thumb set, where most common instructions are 16-bit

There is a w suffix for thumb-2 instruction as below, how does it change the semantic of the instruction without it? The search result is very noisy and I didn't get the answer. addw r0, r1, #0 I see ADDW in Cortex-M3 TRM Table 2-5 Data operations with large immediate ADDW and SUBW have a 12-bit immediate. This means they can replace many from memory literal loads. It is also mentioned in Quick Reference add wide T2 ADD Rd, Rn, #<imm12> Looks like the assembler would recognize the immediate constant <= 12 bits, and do the needful. In the context where you see it, it is an ordinary "add".

I am trying to mix ARM and THUMB instructions in my assembly code. For example, in the following code I try to use both modes: .thumb @ .code 16 .section __TEXT,__text .globl mySymbol1 mySymbol1: .... .arm @ .code 32 .section __TEXT,__text .globl mySymbol2 mySymbol2: ... Now, as per my understanding when I compile this code into a library and run it through nm, mysymbol1 should show up as arm and mysymbol2 should show up as thumb, i.e, 0000xxxx (__TEXT,__text) external mySymbol1 0000yyyy (__TEXT,__text) external [Thumb] mySymbol2 But both are showing up as arm. What am I missing here? My

I'm facing a weird issue, somewhat similar to this . I have a Windows Phone 8 native DLL project, mostly C++ but with an ARM assembly source in it. The source is in ARM mode (i. e. not Thumb). C++ is compiled to Thumb. The app crashes when C++ tries to call into an assembly routine. The call command in the disassembly is BLX with an immediate offset - it's supposed to switch mode back to ARM, unconditionally, but somehow it doesn't. I have the details of the exception. The exception code is 0xc000001d (invalid operation), and the value of the PC in the crash context struct is 0x696d5985. That

I'm trying to reduce the size of my elf executable. I'm compiling with -ffunction-sections -fdata-sections and linking with -gc-sections , but it appears some of the symbols that I believe are unused are not being discarded. Is there some command in the GNU toolchain I can run to find out which symbols are being used and where? Toolchain: GNU arm-none-eabi Platform: Cortex-M4 Language: C++ Here are my typical build flags: Compilation: arm-none-eabi-g++.exe -Wall -O3 -mthumb -std=c++11 -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=softfp -fsingle-precision-constant -ffunction-sections -fdata

What does the following line do in arm assembly: 000031e6 2916 cmp r1, #22 000031e8 bf1a itte ne I get the first line (comparing r1 to 22) but what about the second line (I've never seen the itte command before and googling returned nothing) It is the ARM's IF-THEN-ELSE instruction, which was introduced in the Thumb-2 instruction set. (Based on your specific example above, it would have been helpful if you had shown the next 3 instructions that followed the ITTE instruction, you'll understand why when you're done reading this answer.) This instruction is used for handling small sequences of

I'm trying to learn skills useful in firmware modding (for which i don't have source code) These questions concern use of BX from thumb code to jump or call other existing thumb code. How do i use BX to JUMP to existing firmware THUMB code, from my THUMB code. How do i use BX to CALL an existing THUMB function (must set LR first), from my THUMB code. My understanding is that cpu looks at lsb bit (bit 0) and i have to make sure this is set to 1 in order to keep cpu state to "thumb state". So I guess i have to ADD 1, to set lsb bit to 1. So ...say i want to just JUMP to 0x24000 ( in the middle

I am a bit confused about instruction sets. There are Thumb, ARM and Thumb 2. From what I have read Thumb instructions are all 16-bit but inside the ARMv7M user manual (page vi) there are Thumb 16-bit and Thumb 32-bit instructions mentioned. Now I have to overcome this confusion. It is said that Thumb 2 supports 16-bit and 32-bit instructions. So is ARMv7M in fact supporting Thumb 2 instructions and not just Thumb? One more thing. Can I say that Thumb (32-bit) is the same as ARM instructions which are allso 32-bit? Oh, ARM and their silly naming... It's a common misconception, but officially