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system call number

The number a program puts in a register to say which kernel service it wants, for example 1 for write on x86-64 Linux.

A system call number selects a kernel service; Linux keeps them stable per ISA (x86-64 in rax: write = 1, exit = 60; ARM64 in x8 and RISC-V in a7: write = 64, exit = 93), while macOS and Windows do not promise stable numbers.

Examples

  • On x86-64 Linux, write is system call 1 and exit is 60.

See also

system call system call wrapper ntdll
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