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So I am working on a debugger for linux s390x system and have the whole disassembler etc set up for reading the ELF file. For debugger I just run it on the process with base address from the process maps.

Now when running for debugger, the process map doesn't have a read only map which would only have ELF headers and this map also does not have the ELF magic bytes in the starting unlike other systems like linux x86_64 and linux arm64. Now this affects my debugger as the addresses are set according to this.

Also to set up the breakpoint ptrace provides the #define S390_BREAKPOINT_U16 ((__u16)0x0001)

Now when set the this at the opcode, it hits the breakpoint correctly, but when I replace the original opcode, the opcode 4 bytes ahead gets placed at this position for some reason.

I think most probably the ELF header magic bytes missing messes up stuff, even if i set the breakpoint to start of a function like main SIGILL is hit some

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