On Tue, 16 Aug 2022 at 19:17, Andre Przywara andre.przywara@arm.com wrote:
On Wed, 10 Aug 2022 12:04:46 +0300 Sergei Antonov saproj@gmail.com wrote:
Hi,
There is currently a problem that U-Boot can not work on ARMv4 because assembly imlementations of memcpy() and some other functions use "bx lr" instruction that is not available on ARMv4 ("mov pc, lr" should be used instead).
So there is a comment in the current code, right above what's shown here in the first hunk, which says: /*
- We only support cores that support at least Thumb-1 and thus we use
- 'bx lr'
*/
I did not notice it. Thanks.
This was added by Tom in commit 431afb4ef9fe, when he removed some code very close to what you are adding back now.
So what is the story here? This commit seems to suggest U-Boot doesn't support even ARMv5 without "T", has this changed? There are probably other code places which would need adjustment to run on ARMv4?
I can not explain why there was __ARM_ARCH_5E__ in the removed code. I am dealing with the issue that ARMv4 ("four" without letter "t") does not understand "bx lr" while ARMv4T does. The device on which I run modern U-Boot has FA526 - a CPU similar to ARM810 which is ARMv4 without Thumb. Its MIDR register is 0x66015261 which means that Architecture=1.
Tom, can you say why support for Thumb-less code / older architectures was dropped? No users, I guess?
Sergei, can you say what is this for? Are you adding support for a SoC with an ARM810 core from 1996?
Yes. And U-Boot for this device is already working: able to boot Linux and do TFTP stuff. My company is going to use it on hundreds of devices. It would be great for us to not have to patch U-Boot locally and have ARMv4-compatible assembly in the mainline.