^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 1) ===============================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 2) Power Architecture 64-bit Linux system call ABI
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 3) ===============================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 4)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 5) syscall
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 6) =======
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 7)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 8) Invocation
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 9) ----------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10) The syscall is made with the sc instruction, and returns with execution
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11) continuing at the instruction following the sc instruction.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13) If PPC_FEATURE2_SCV appears in the AT_HWCAP2 ELF auxiliary vector, the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14) scv 0 instruction is an alternative that may provide better performance,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15) with some differences to calling sequence.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17) syscall calling sequence\ [1]_ matches the Power Architecture 64-bit ELF ABI
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18) specification C function calling sequence, including register preservation
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19) rules, with the following differences.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21) .. [1] Some syscalls (typically low-level management functions) may have
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22) different calling sequences (e.g., rt_sigreturn).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24) Parameters
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25) ----------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26) The system call number is specified in r0.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) There is a maximum of 6 integer parameters to a syscall, passed in r3-r8.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30) Return value
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31) ------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32) - For the sc instruction, both a value and an error condition are returned.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33) cr0.SO is the error condition, and r3 is the return value. When cr0.SO is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 34) clear, the syscall succeeded and r3 is the return value. When cr0.SO is set,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 35) the syscall failed and r3 is the error value (that normally corresponds to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 36) errno).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 37)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 38) - For the scv 0 instruction, the return value indicates failure if it is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 39) -4095..-1 (i.e., it is >= -MAX_ERRNO (-4095) as an unsigned comparison),
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 40) in which case the error value is the negated return value.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 41)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 42) Stack
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 43) -----
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 44) System calls do not modify the caller's stack frame. For example, the caller's
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 45) stack frame LR and CR save fields are not used.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 46)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 47) Register preservation rules
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 48) ---------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 49) Register preservation rules match the ELF ABI calling sequence with the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 50) following differences:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 51)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 52) +------------------------------------------------------------------------+
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 53) | For the sc instruction, differences with the ELF ABI |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 54) +--------------+--------------+------------------------------------------+
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 55) | r0 | Volatile | (System call number.) |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 56) | rr3 | Volatile | (Parameter 1, and return value.) |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 57) | rr4-r8 | Volatile | (Parameters 2-6.) |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 58) | rcr0 | Volatile | (cr0.SO is the return error condition.) |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 59) | rcr1, cr5-7 | Nonvolatile | |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 60) | rlr | Nonvolatile | |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 61) +--------------+--------------+------------------------------------------+
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 62) | For the scv 0 instruction, differences with the ELF ABI |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 63) +--------------+--------------+------------------------------------------+
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 64) | r0 | Volatile | (System call number.) |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 65) | r3 | Volatile | (Parameter 1, and return value.) |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 66) | r4-r8 | Volatile | (Parameters 2-6.) |
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 67) +--------------+--------------+------------------------------------------+
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 68)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 69) All floating point and vector data registers as well as control and status
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 70) registers are nonvolatile.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 71)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 72) Transactional Memory
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 73) --------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 74) Syscall behavior can change if the processor is in transactional or suspended
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 75) transaction state, and the syscall can affect the behavior of the transaction.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 76)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 77) If the processor is in suspended state when a syscall is made, the syscall
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 78) will be performed as normal, and will return as normal. The syscall will be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 79) performed in suspended state, so its side effects will be persistent according
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 80) to the usual transactional memory semantics. A syscall may or may not result
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 81) in the transaction being doomed by hardware.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 82)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 83) If the processor is in transactional state when a syscall is made, then the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 84) behavior depends on the presence of PPC_FEATURE2_HTM_NOSC in the AT_HWCAP2 ELF
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 85) auxiliary vector.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 86)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 87) - If present, which is the case for newer kernels, then the syscall will not
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 88) be performed and the transaction will be doomed by the kernel with the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 89) failure code TM_CAUSE_SYSCALL | TM_CAUSE_PERSISTENT in the TEXASR SPR.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 90)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 91) - If not present (older kernels), then the kernel will suspend the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 92) transactional state and the syscall will proceed as in the case of a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 93) suspended state syscall, and will resume the transactional state before
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 94) returning to the caller. This case is not well defined or supported, so this
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 95) behavior should not be relied upon.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 96)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 97) scv 0 syscalls will always behave as PPC_FEATURE2_HTM_NOSC.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 98)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 99) ptrace
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 100) ------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 101) When ptracing system calls (PTRACE_SYSCALL), the pt_regs.trap value contains
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 102) the system call type that can be used to distinguish between sc and scv 0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 103) system calls, and the different register conventions can be accounted for.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 104)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 105) If the value of (pt_regs.trap & 0xfff0) is 0xc00 then the system call was
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 106) performed with the sc instruction, if it is 0x3000 then the system call was
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 107) performed with the scv 0 instruction.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 108)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 109) vsyscall
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 110) ========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 111)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 112) vsyscall calling sequence matches the syscall calling sequence, with the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 113) following differences. Some vsyscalls may have different calling sequences.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 114)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 115) Parameters and return value
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 116) ---------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 117) r0 is not used as an input. The vsyscall is selected by its address.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 118)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 119) Stack
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 120) -----
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 121) The vsyscall may or may not use the caller's stack frame save areas.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 122)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 123) Register preservation rules
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 124) ---------------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 125)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 126) =========== ========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 127) r0 Volatile
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 128) cr1, cr5-7 Volatile
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 129) lr Volatile
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 130) =========== ========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 131)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 132) Invocation
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 133) ----------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 134) The vsyscall is performed with a branch-with-link instruction to the vsyscall
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 135) function address.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 136)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 137) Transactional Memory
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 138) --------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 139) vsyscalls will run in the same transactional state as the caller. A vsyscall
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 140) may or may not result in the transaction being doomed by hardware.
Orange Pi5 kernel
Deprecated Linux kernel 5.10.110 for OrangePi 5/5B/5+ boards
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