thumb

Does arm-none-eabi-ld rewrite the bl instruction?

由 淺唱寂寞╮ 提交于 2019-12-12 05:30:45
问题 I'm trying to understand why some Cortex-M0 code behaves differently when it is linked versus unlinked. In both cases it is loaded to 0x20000000 . It looks like despite my best efforts to generate position independent code by passing -fPIC to the compiler, the bl instruction appears to differ after the code has passed through the linker. Am I reading this correctly, is that just a part of the linker's job in ARM Thumb, and is there a better way to generate a position independent function call

How do I optimise a filter loop for Cortex-M3?

由 匆匆过客 提交于 2019-12-11 12:43:12
问题 I just need to alter the code so that it does the same basic function but more optimised, basically I think the filter loop is the main piece of code that can be changed as I feel there are too many instructions in there, but don't know where to start with it. I am working with the Cortex M3 and Thumb 2. I have tried tampering with the filter loop, so that I could add the previous number stored in the register and divide that by 8, but I do not know how to really execute that. ; Perform in

No qsort_r for Android (or how to disable force Thumb to use CLZ in Android ARM code)

由 送分小仙女□ 提交于 2019-12-11 01:31:32
问题 What I want to do (high-level): use qsort_r on Android. There is no default implementation. So I've grabbed one from BSD. Unfortunately it needs fls functions which is also unavailable on Android. So I've grabbed Apple Open Source Libc library and copied ARM implementation into an inline assembly. Now I'm getting this: Assembler messages: Error: selected processor does not support Thumb mode `clz r3,r0' Error: cannot honor width suffix -- `rsb r0,r3,#32' AFAIR ARM-6 doesn't support it in

ARM-C Inter-working

由 孤街醉人 提交于 2019-12-10 21:36:10
问题 I am trying out a simple program for ARM-C inter-working. Here is the code: #include<stdio.h> #include<stdlib.h> int Double(int a); extern int Start(void); int main(){ int result=0; printf("in C main\n"); result=Start(); printf("result=%d\n",result); return 0; } int Double(int a) { printf("inside double func_argument_value=%d\n",a); return (a*2); } The assembly file goes as- .syntax unified .cpu cortex-m3 .thumb .align .global Start .global Double .thumb_func Start: mov r10,lr mov r0,#42 bl

Calling ARM assembly from C, GCC (bare metal)

由 若如初见. 提交于 2019-12-09 06:29:02
问题 I am trying to do some bare-metal programming in ARM with GCC and testing on QEMU. Whenever I call into an ARM label from C, my program hangs. I have a simple example of code that shows the problem at https://gist.github.com/1654392 -- when I call activate() in that code, it hangs. I have observed with objdump that when I do a bl from assembly to C code (as from _start) it is generating a small wrapper that switches to thumb instructions. It seems that the C code is all being generated in

About arm pc value in thumb 16/32bits mixed instructions stream

由 偶尔善良 提交于 2019-12-08 23:15:30
I read a couple of articles including question here in SO Why does the ARM PC register point to the instruction after the next one to be executed? , that pc register value is actually current executing instruction address plus 2 instructions ahead, so in ARM state it's +8 byte (2*32bits). My question is that, for thumb state, there could be 16bits or 32bits instructions, does it mean that the fetching pc address could be an offset of +4 bytes OR +8 bytes for 16/32bits instructions respectively? For example: 279ae6: f8df 9338 ldr.w r9, [pc, #824] --> pc value= 279aea or 279aee 279aea: f44f 7380

LPC4088 checksum value for Thumb?

由 余生颓废 提交于 2019-12-08 05:23:19
问题 In the LPC4088 user manual (p. 876) we can read that LPC4088 microcontroler has a really extraordinary startup procedure: This looks like a total nonsense and I need someone to help me clear things out... In the world of ARM I've heard countless times to put vector table looking like this: reset: b _start undefined: b undefined software_interrupt: b software_interrupt prefetch_abort: b prefetch_abort data_abort: b data_abort nop interrupt_request: b interrupt_request fast_interrupt_request: b

About arm pc value in thumb 16/32bits mixed instructions stream

由 假如想象 提交于 2019-12-08 05:00:31
问题 I read a couple of articles including question here in SO Why does the ARM PC register point to the instruction after the next one to be executed?, that pc register value is actually current executing instruction address plus 2 instructions ahead, so in ARM state it's +8 byte (2*32bits). My question is that, for thumb state, there could be 16bits or 32bits instructions, does it mean that the fetching pc address could be an offset of +4 bytes OR +8 bytes for 16/32bits instructions respectively

How to generate the machine code of Thumb instructions?

由 断了今生、忘了曾经 提交于 2019-12-06 13:21:40
I searched Google for generating machine code of ARM instructions, such as this one Converting very simple ARM instructions to binary/hex The answer referenced ARM7TDMI-S Data Sheet (ARM DDI 0084D). The diagram of data processing instructions is good enough. Unfortunately, it's for ARM instructions, not for Thumb/Thumb-2 instructions. Take the B instruction as an example. ARM Architecture Reference Manual - ARMv7-A and ARMv7-R edition section A8.8.18, Encoding T4: For the assembly code: B 0x50 How can I encode the immediate value 0x50 into the 4-byte machine code? Or if I want to write a C

difference between ldr and ldr.w

由 寵の児 提交于 2019-12-06 02:47:31
问题 I recently had to debug a MachO binary and I came across the following instruction :- ldr.w r4, [r1, r0, lsl #2] I understand that ldr r4, [r1, r0, lsl #2] shifts r0 to the left two times, adds it to r1 and dereferences the result. How is ldr.w different? 回答1: .W is an optional instruction width specifier. It doesn't affect the behaviour of the instruction as such, it just ensures that a 32 bit instruction is generated. See infocenter.arm.com for details: LDR (pc-relative) in Thumb-2 You can
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