1 ==============================================
2 Power Architecture 64-bit Linux system call AB
3 ==============================================
4
5 syscall
6 =======
7
8 Invocation
9 ----------
10 The syscall is made with the sc instruction, a
11 continuing at the instruction following the sc
12
13 If PPC_FEATURE2_SCV appears in the AT_HWCAP2 E
14 scv 0 instruction is an alternative that may p
15 with some differences to calling sequence.
16
17 syscall calling sequence\ [1]_ matches the Pow
18 specification C function calling sequence, inc
19 rules, with the following differences.
20
21 .. [1] Some syscalls (typically low-level mana
22 different calling sequences (e.g., rt_s
23
24 Parameters
25 ----------
26 The system call number is specified in r0.
27
28 There is a maximum of 6 integer parameters to
29
30 Return value
31 ------------
32 - For the sc instruction, both a value and an
33 cr0.SO is the error condition, and r3 is the
34 clear, the syscall succeeded and r3 is the r
35 the syscall failed and r3 is the error value
36 errno).
37
38 - For the scv 0 instruction, the return value
39 -4095..-1 (i.e., it is >= -MAX_ERRNO (-4095)
40 in which case the error value is the negated
41
42 Stack
43 -----
44 System calls do not modify the caller's stack
45 stack frame LR and CR save fields are not used
46
47 Register preservation rules
48 ---------------------------
49 Register preservation rules match the ELF ABI
50 differences.
51
52 For the sc instruction, the differences from t
53
54 +--------------+--------------------+---------
55 | Register | Preservation Rules | Purpose
56 +==============+====================+=========
57 | r0 | Volatile | (System
58 +--------------+--------------------+---------
59 | r3 | Volatile | (Paramet
60 +--------------+--------------------+---------
61 | r4-r8 | Volatile | (Paramet
62 +--------------+--------------------+---------
63 | cr0 | Volatile | (cr0.SO
64 +--------------+--------------------+---------
65 | cr1, cr5-7 | Nonvolatile |
66 +--------------+--------------------+---------
67 | lr | Nonvolatile |
68 +--------------+--------------------+---------
69
70 For the scv 0 instruction, the differences fro
71
72 +--------------+--------------------+---------
73 | Register | Preservation Rules | Purpose
74 +==============+====================+=========
75 | r0 | Volatile | (System
76 +--------------+--------------------+---------
77 | r3 | Volatile | (Paramet
78 +--------------+--------------------+---------
79 | r4-r8 | Volatile | (Paramet
80 +--------------+--------------------+---------
81
82 All floating point and vector data registers a
83 registers are nonvolatile.
84
85 Transactional Memory
86 --------------------
87 Syscall behavior can change if the processor i
88 transaction state, and the syscall can affect
89
90 If the processor is in suspended state when a
91 will be performed as normal, and will return a
92 performed in suspended state, so its side effe
93 to the usual transactional memory semantics. A
94 in the transaction being doomed by hardware.
95
96 If the processor is in transactional state whe
97 behavior depends on the presence of PPC_FEATUR
98 auxiliary vector.
99
100 - If present, which is the case for newer kern
101 be performed and the transaction will be doo
102 failure code TM_CAUSE_SYSCALL | TM_CAUSE_PER
103
104 - If not present (older kernels), then the ker
105 transactional state and the syscall will pro
106 suspended state syscall, and will resume the
107 returning to the caller. This case is not we
108 behavior should not be relied upon.
109
110 scv 0 syscalls will always behave as PPC_FEATU
111
112 ptrace
113 ------
114 When ptracing system calls (PTRACE_SYSCALL), t
115 the system call type that can be used to disti
116 system calls, and the different register conve
117
118 If the value of (pt_regs.trap & 0xfff0) is 0xc
119 performed with the sc instruction, if it is 0x
120 performed with the scv 0 instruction.
121
122 vsyscall
123 ========
124
125 vsyscall calling sequence matches the syscall
126 following differences. Some vsyscalls may have
127
128 Parameters and return value
129 ---------------------------
130 r0 is not used as an input. The vsyscall is se
131
132 Stack
133 -----
134 The vsyscall may or may not use the caller's s
135
136 Register preservation rules
137 ---------------------------
138
139 =========== ========
140 r0 Volatile
141 cr1, cr5-7 Volatile
142 lr Volatile
143 =========== ========
144
145 Invocation
146 ----------
147 The vsyscall is performed with a branch-with-l
148 function address.
149
150 Transactional Memory
151 --------------------
152 vsyscalls will run in the same transactional s
153 may or may not result in the transaction being
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