thumb

I'm working on an iPhone/iPad project, and I want to update the status register during some (not all) arithmetic operations. By default, Xcode uses 'Compile for Thumb' and I don't want to change it. The following GCC inline assembly code works fine under ARM, but results in a compile error under Thumb: 'instruction not supported in Thumb16 mode - adds r6,r4,r5'. The problem lies in the status register update. (I'm also aware that movcs and strcs will need to be changed). Does Thumb have an ADD instruction which sets Overflow (V) or Carry (C) in the CPSR? If not, are there Thumb-specific

I've read through much of the ARM documentation but still having trouble decoding a BLX instruction. Here are two examples: __text:0000347C 02 F0 B2 ED BLX _objc_msgSend __text:0000469C 01 F0 A2 EC BLX _objc_msgSend Both of these are supposed to go to the same place, virtual address 0x5FE4 as seen here: __symbolstub1:00005FE4 38 F0 9F E5 LDR PC, =__imp__objc_msgSend However, I can't figure out what calculation is used to get from the above two addresses (0x347C and 0x469C) using their instruction bytes. According to the ARM documentation its supposed to be a relative jump, using a right shift

I'm trying to disassemble an object built for ARM with gcc. Unfortunately, objdump is trying to guess whether the code is ARM and Thumb, and is getting it wrong: it thinks my code is Thumb when it's actually ARM. I see that objdump has an option to force it to interpret all instructions as Thumb ( -Mforce-thumb ), but it doesn't have one to force ARM mode! This seems like a really weird omission to me, and it's seriously hampering my ability to get work done (I'm on an embedded device and my only means of debugging is to look at the disassembly). I've tried various approaches, including trying

I've heard it might be a good idea to turn off "compile for thumb" in an iPhone target's settings to increase performance. I'm having some trouble finding this setting though. Since I couldn't find it in my current project, I decided to make a new one (where I could find and set it), and copy my files over to it (and also update all libs I'm using at the same time). But now it seems like this setting has disapperad from this new project also. No matter what SDK I choose, simulator or device, the setting will not show up in the target settings! I do seem however to still have a variable called

I was wondering if anyone had any hard numbers on ARM vs Thumb code performance on iPhone 3GS. Specifically for non-floating point (VFP or NEON) code - I'm aware of the issues with floating point performance in Thumb mode. Is there a point where the extra code size of bigger ARM instructions becomes a performance hazard? In other words, if my executable code is relatively small compared to available memory, is there any measured performance difference to turning Thumb mode on? The reason I ask is that while I can enable ARM for the NEON specific source files in Xcode using the "-marm" option,