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agra-uni-bremen / riscv-vp

RISC-V Virtual Prototype
MIT License
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ELF loader does not expect zero length section #6

Closed U2654 closed 3 years ago

U2654 commented 3 years ago

Using the hifive1 toolchain, I can produce an ELF file (ld script ok and with --gc-sections) with the following header:

    LOAD off    0x00001000 vaddr 0x20400000 paddr 0x20400000 align 2**12 
         filesz 0x000000c0 memsz 0x000000c0 flags r-x 
    LOAD off    0x000010c0 vaddr 0x00000000 paddr 0x00000000 align 2**12
         filesz 0x00000000 memsz 0x00000000 flags --- <br> 
    NULL off    0x00000000 vaddr 0x80000000 paddr 0x80000000 align 2**0
         filesz 0x00000000 memsz 0x00000400 flags rw- <br>

I cannot check if this would be a problem with a real hifive1 board (I have only a rev b). However, the ELF loader of the vp throws an error in elf_loader.h:51 (assert fails) as the second LOAD section is a strange entry. I could easily fix this but do not know if the problem would appear on real hardware. Any suggestion?

Cirromulus commented 3 years ago

It is actually strange, because it continues the first section with zero length, and both sections write to the read-only MaskROM. Does this happen with other files as well?

Edit: Especially interesting would be the linker-script.

FIY: image

U2654 commented 3 years ago

It quite interesting that this effects relates to --gc-sections as I mentioned. This is without:

Program Header:
    LOAD off    0x00001000 vaddr 0x20400000 paddr 0x20400000 align 2**12
         filesz 0x00000104 memsz 0x00000104 flags r-x
    LOAD off    0x00002000 vaddr 0x80000000 paddr 0x20400104 align 2**12
         filesz 0x00000000 memsz 0x00000000 flags rw-
    NULL off    0x00000000 vaddr 0x80000000 paddr 0x80000000 align 2**0
         filesz 0x00000000 memsz 0x00000800 flags rw-

I'll provide the example.

U2654 commented 3 years ago

Here is an example.

https://github.com/U2654/embedded/tree/master/workspace/demo_led

Cirromulus commented 3 years ago

There has to be a problem with your linkerscripts. When building the examples from sifive-hifive1, only sections 0x20400000 and 0x80000000 are present.

U2654 commented 3 years ago

Actually, the linker script is from the freedom-bsp except the entry. However, I'll check yours out.

Cirromulus commented 3 years ago

I misinterpreted your output - offs is not equal to the paddr.

The Linker produces an empty section (N°2). This is unhandled in the loader, as a zero-length section does not make sense.

U2654 commented 3 years ago

OK. I checked the linker script. The only difference is the ENTRY-point. Thus, I wonder if you could reproduce the result?

Actually, the workaround is obvious. Shall I do a pull request?