I have compiled a simple binary file (hello.bin) and stored it on a memory card.
I am running a NXP Sabre dev kit with i.mx 6 quad processor. I have started up U-boot and am trying to access the binary file and make it run.
The hello.bin is availiable because the following command works:
=> fatload mmc 1:4 0x20005000 hello.bin
reading hello.bin
The way I understand it the file should be loaded into RAM at the address 0x20005000
So I want to test that the binary is there
=> md 0x20005000
20005000: 464c457f 00010101 00000000 00000000 .ELF............
20005010: 00280002 00000001 00010315 00000034 ..(.........4...
20005020: 000028f4 05000400 00200034 00280009 .(......4. ...(.
20005030: 00240025 70000001 00000454 00010454 %.$....pT...T...
Looks all right, as the starting bits are matching the file I copied to SD-card.
When I try to start the binary, the device reports undefined instruction:
=> go 0x20005000
## Starting application at 0x20005000 ...
undefined instruction
pc : [<20005158>] lr : [<4ff71403>]
reloc pc : [<e7897158>] lr : [<17803403>]
sp : 4f56dd50 ip : 00000000 fp : 00000002
r10: 4f56f938 r9 : 4f56deb0 r8 : 4ffc3c40
r7 : 4ff713d9 r6 : 00000002 r5 : 20005000 r4 : 4f56f93c
r3 : 20005000 r2 : 4f56f93c r1 : 4f56f93c r0 : 00000000
Flags: nzCv IRQs off FIQs off Mode SVC_32
Resetting CPU ...
Got some help from another friend, I found it very helpful so I will post it:
You can use the Yocto toolchain but you cannot link against the C library (which is done by default) so you have to put some extra options to GCC to let it know that, also, you cannot use the go instruction from U-Boot to jump to an ELF binary that you just loaded in memory, the ELF binary has to be converted to a 'raw' binary (list of ARM instructions in your case) with the tool objdump. An ELF binary it's a specific format that encapsulate your code/your data and some extra information, and the first part of the ELF is the description of the binary, so right now, when you do a go at the first address, you are trying to tell the CPU to execute something which is not an ARM instruction. You basically want to execute what we call the '.text' section of the ELF binary.