Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 140 insertions, 0 deletions

diff --git a/Documentation/powerpc/syscall64-abi.rst b/Documentation/powerpc/syscall64-abi.rst
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+===============================================
+Power Architecture 64-bit Linux system call ABI
+===============================================
+
+syscall
+=======
+
+Invocation
+----------
+The syscall is made with the sc instruction, and returns with execution
+continuing at the instruction following the sc instruction.
+
+If PPC_FEATURE2_SCV appears in the AT_HWCAP2 ELF auxiliary vector, the
+scv 0 instruction is an alternative that may provide better performance,
+with some differences to calling sequence.
+
+syscall calling sequence\ [1]_ matches the Power Architecture 64-bit ELF ABI
+specification C function calling sequence, including register preservation
+rules, with the following differences.
+
+.. [1] Some syscalls (typically low-level management functions) may have
+       different calling sequences (e.g., rt_sigreturn).
+
+Parameters
+----------
+The system call number is specified in r0.
+
+There is a maximum of 6 integer parameters to a syscall, passed in r3-r8.
+
+Return value
+------------
+- For the sc instruction, both a value and an error condition are returned.
+  cr0.SO is the error condition, and r3 is the return value. When cr0.SO is
+  clear, the syscall succeeded and r3 is the return value. When cr0.SO is set,
+  the syscall failed and r3 is the error value (that normally corresponds to
+  errno).
+
+- For the scv 0 instruction, the return value indicates failure if it is
+  -4095..-1 (i.e., it is >= -MAX_ERRNO (-4095) as an unsigned comparison),
+  in which case the error value is the negated return value.
+
+Stack
+-----
+System calls do not modify the caller's stack frame. For example, the caller's
+stack frame LR and CR save fields are not used.
+
+Register preservation rules
+---------------------------
+Register preservation rules match the ELF ABI calling sequence with the
+following differences:
+
++------------------------------------------------------------------------+
+|        For the sc instruction, differences with the ELF ABI		 |
++--------------+--------------+------------------------------------------+
+| r0           | Volatile     | (System call number.)			 |
+| rr3          | Volatile     | (Parameter 1, and return value.)	 |
+| rr4-r8       | Volatile     | (Parameters 2-6.)			 |
+| rcr0         | Volatile     | (cr0.SO is the return error condition.)	 |
+| rcr1, cr5-7  | Nonvolatile  |						 |
+| rlr          | Nonvolatile  |						 |
++--------------+--------------+------------------------------------------+
+|      For the scv 0 instruction, differences with the ELF ABI		 |
++--------------+--------------+------------------------------------------+
+| r0           | Volatile     | (System call number.)			 |
+| r3           | Volatile     | (Parameter 1, and return value.)	 |
+| r4-r8        | Volatile     | (Parameters 2-6.)			 |
++--------------+--------------+------------------------------------------+
+
+All floating point and vector data registers as well as control and status
+registers are nonvolatile.
+
+Transactional Memory
+--------------------
+Syscall behavior can change if the processor is in transactional or suspended
+transaction state, and the syscall can affect the behavior of the transaction.
+
+If the processor is in suspended state when a syscall is made, the syscall
+will be performed as normal, and will return as normal. The syscall will be
+performed in suspended state, so its side effects will be persistent according
+to the usual transactional memory semantics. A syscall may or may not result
+in the transaction being doomed by hardware.
+
+If the processor is in transactional state when a syscall is made, then the
+behavior depends on the presence of PPC_FEATURE2_HTM_NOSC in the AT_HWCAP2 ELF
+auxiliary vector.
+
+- If present, which is the case for newer kernels, then the syscall will not
+  be performed and the transaction will be doomed by the kernel with the
+  failure code TM_CAUSE_SYSCALL | TM_CAUSE_PERSISTENT in the TEXASR SPR.
+
+- If not present (older kernels), then the kernel will suspend the
+  transactional state and the syscall will proceed as in the case of a
+  suspended state syscall, and will resume the transactional state before
+  returning to the caller. This case is not well defined or supported, so this
+  behavior should not be relied upon.
+
+scv 0 syscalls will always behave as PPC_FEATURE2_HTM_NOSC.
+
+ptrace
+------
+When ptracing system calls (PTRACE_SYSCALL), the pt_regs.trap value contains
+the system call type that can be used to distinguish between sc and scv 0
+system calls, and the different register conventions can be accounted for.
+
+If the value of (pt_regs.trap & 0xfff0) is 0xc00 then the system call was
+performed with the sc instruction, if it is 0x3000 then the system call was
+performed with the scv 0 instruction.
+
+vsyscall
+========
+
+vsyscall calling sequence matches the syscall calling sequence, with the
+following differences. Some vsyscalls may have different calling sequences.
+
+Parameters and return value
+---------------------------
+r0 is not used as an input. The vsyscall is selected by its address.
+
+Stack
+-----
+The vsyscall may or may not use the caller's stack frame save areas.
+
+Register preservation rules
+---------------------------
+
+=========== ========
+r0          Volatile
+cr1, cr5-7  Volatile
+lr          Volatile
+=========== ========
+
+Invocation
+----------
+The vsyscall is performed with a branch-with-link instruction to the vsyscall
+function address.
+
+Transactional Memory
+--------------------
+vsyscalls will run in the same transactional state as the caller. A vsyscall
+may or may not result in the transaction being doomed by hardware.