[Letux-kernel] LX20 prototype is booting

[H. Nikolaus Schaller]

Hi Paul,

> Am 06.05.2025 um 01:02 schrieb Paul Boddie <paul at boddie.org.uk>:
> 
> On 2025-05-05 22:27, H. Nikolaus Schaller wrote:
>> For the exec() problem I could now trace it down to arch_check_elf() in arch/mips/kernel/elf.c
>> And specifically:
>> https://elixir.bootlin.com/linux/v6.1.28/source/arch/mips/kernel/elf.c#L166
> 
> That is some verbose code, but highly readable, I suppose.
> 
>> But I have no idea why. And why only for x2000 and not x1600.
>> Values are:
>> [    0.017085] arch_check_elf elf32=1
>> [    0.017085] arch_check_elf flags=10001007
>> which means that EF_MIPS_NAN2008 (=0x00000400) is not set in the flags.
>> And mips_use_nan_legacy is not set at all.
>> So either the header is not read properly (alignment issue?) or the mips_use_nan_legacy
>> should be set... Which may be correct that it is not set. Then we have a problem.

I checked the header on some ARM Linux.

root at letux:~# readelf -a /media/sdb/rootfs/sbin/init
ELF Header:
  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00
  Class:                             ELF32
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           MIPS R3000
  Version:                           0x1
  Entry point address:               0x401d10
  Start of program headers:          52 (bytes into file)
  Start of section headers:          39480 (bytes into file)
  Flags:                             0x10001007, noreorder, pic, cpic, o32, mips2
  Size of this header:               52 (bytes)
  Size of program headers:           32 (bytes)
  Number of program headers:         11
  Size of section headers:           40 (bytes)
  Number of section headers:         31
  Section header string table index: 30

...

The "Flags" appear to be correct as the x2000 arch_check_elf() is finding them.

So we are missing the mips_use_nan_legacy flag.

> Now, I did read something recently, maybe related to GCC or perhaps Debian, about older XBurst implementations not supporting the appropriate MIPS floating-point semantics. This may have complicated the situation for MIPS32 in Debian, leading to its relegation to only getting support from a third party in future releases.

Well, that should indeed influence future development.
But here I am using good old Jessie which is working fine on all other Ingenic
MIPS devices.

Therefore I think we have some bug in architecture setup. Maybe the x2000 is not
set up as compatible for R3000, o32, mips2?

BR,
Nikolaus