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I am currently implementing a C runtime library for the Arm64 platform, and I am unsure which assumptions I can make about the environment at the precise point that the application is executed (what the ELF file has defined as the entry point). With environment, I am primarily referring to the stack setup and the cpu registers.

I was able to piece together information by looking at the kernel source code, but not everything.

My question is: Is the calling convention into applications documented and/or standardized? I am looking for something equivalent to Arm64 Base Procedure Call Standard for example.

I am posting this in the Unix & Linux Stack Exchange, because I am interested in Linix specifically, and I assume an operating system may perform this call in anyway it defines as long as all executables conform.

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  • This being a vast topic with a fair number of exceptions. I suggest that you first read the manual for the execve function of the standard C libray, then eventually come back here re-editing your question with the points for which you need more detailed infos.
    – MC68020
    CommentedJan 4, 2023 at 15:42
  • After looking into it some more, I agree. The scope is too great. Though the execve documentation is not quite the level of detail I am looking for, I found such information e.g. in the create_flat_tables() kernel function. I will edit my question
    – lte678
    CommentedJan 4, 2023 at 16:55

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Unfortunately, it seems that process initialization is not present in the System V ABI Standard for the Armv8 platform (Source: ARM's published ABIs), despite being present in other versions of the standard.

It does appear to be a part of the standard though, and I was able to find the answers to the question in the AMD64 SystemV ABI, v0.99.

Summarizing the contents very briefly, process initialization consists of

  • Putting argc, argv and envp (and their data) on the stack
  • Floating point operations should be enabled
  • Register state is not relevant, except for the stack pointer (and in some cases the frame pointer and a pointer for atexit())
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