Register Usage for Linux/PA-RISC | Linux 6.18.37

요약·해설과 원문, 전문 번역을 서로 분리했습니다. API 이름, symbol, source path는 원문 표기를 사용합니다.

1. 요약·해설

원문의 핵심 논리와 kernel programming 관점의 보충 설명입니다. 아래의 전문 번역과는 별도로 작성했습니다.

요약과 해설

registers.rst:1-154

이 문서는 exception path의 control/space register와 procedure call의 caller/callee-save contract를 연결합니다. Real-mode bit 전환과 shadow register는 interruption latency와 debugging 정확도에 직접 영향을 줍니다.

PA-RISC register layers

Control registersInterruption/MMU/timer

Space registersKernel/user address spaces

PSWTranslation/interrupt state

General registersCall arguments/return/save

Execution state와 procedure ABI의 register 집합입니다.

Call preservation

GroupRegistersPolicy

Caller-clobbered`r1,r2,r19-r26,r28,r29,r31`필요하면 caller 저장

Callee-saved`r3-r18,r27,r30`Callee가 저장·복원

Return`r28,r29`Primary/secondary return

General register의 대표 ABI 역할입니다.

2. 영어 원문 전체

번역 기준이 된 Linux v6.18.37 원문입니다. 줄 번호는 이 버전의 파일 좌표입니다.

원문 전체 펼치기

1 ================================

2 Register Usage for Linux/PA-RISC

3 ================================

5 [ an asterisk is used for planned usage which is currently unimplemented ]

7 General Registers as specified by ABI

8 =====================================

10 Control Registers

11 -----------------

13 =============================== ===============================================

14 CR 0 (Recovery Counter) used for ptrace

15 CR 1-CR 7(undefined) unused

16 CR 8 (Protection ID) per-process value*

17 CR 9, 12, 13 (PIDS) unused

18 CR10 (CCR) lazy FPU saving*

19 CR11 as specified by ABI (SAR)

20 CR14 (interruption vector) initialized to fault_vector

21 CR15 (EIEM) initialized to all ones*

22 CR16 (Interval Timer) read for cycle count/write starts Interval Tmr

23 CR17-CR22 interruption parameters

24 CR19 Interrupt Instruction Register

25 CR20 Interrupt Space Register

26 CR21 Interrupt Offset Register

27 CR22 Interrupt PSW

28 CR23 (EIRR) read for pending interrupts/write clears bits

29 CR24 (TR 0) Kernel Space Page Directory Pointer

30 CR25 (TR 1) User Space Page Directory Pointer

31 CR26 (TR 2) not used

32 CR27 (TR 3) Thread descriptor pointer

33 CR28 (TR 4) not used

34 CR29 (TR 5) not used

35 CR30 (TR 6) current / 0

36 CR31 (TR 7) Temporary register, used in various places

37 =============================== ===============================================

39 Space Registers (kernel mode)

40 -----------------------------

42 =============================== ===============================================

43 SR0 temporary space register

44 SR4-SR7 set to 0

45 SR1 temporary space register

46 SR2 kernel should not clobber this

47 SR3 used for userspace accesses (current process)

48 =============================== ===============================================

50 Space Registers (user mode)

51 ---------------------------

53 =============================== ===============================================

54 SR0 temporary space register

55 SR1 temporary space register

56 SR2 holds space of linux gateway page

57 SR3 holds user address space value while in kernel

58 SR4-SR7 Defines short address space for user/kernel

59 =============================== ===============================================

62 Processor Status Word

63 ---------------------

65 =============================== ===============================================

66 W (64-bit addresses) 0

67 E (Little-endian) 0

68 S (Secure Interval Timer) 0

69 T (Taken Branch Trap) 0

70 H (Higher-privilege trap) 0

71 L (Lower-privilege trap) 0

72 N (Nullify next instruction) used by C code

73 X (Data memory break disable) 0

74 B (Taken Branch) used by C code

75 C (code address translation) 1, 0 while executing real-mode code

76 V (divide step correction) used by C code

77 M (HPMC mask) 0, 1 while executing HPMC handler*

78 C/B (carry/borrow bits) used by C code

79 O (ordered references) 1*

80 F (performance monitor) 0

81 R (Recovery Counter trap) 0

82 Q (collect interruption state) 1 (0 in code directly preceding an rfi)

83 P (Protection Identifiers) 1*

84 D (Data address translation) 1, 0 while executing real-mode code

85 I (external interrupt mask) used by cli()/sti() macros

86 =============================== ===============================================

88 "Invisible" Registers

89 ---------------------

91 =============================== ===============================================

92 PSW default W value 0

93 PSW default E value 0

94 Shadow Registers used by interruption handler code

95 TOC enable bit 1

96 =============================== ===============================================

98 -------------------------------------------------------------------------

100 The PA-RISC architecture defines 7 registers as "shadow registers".

101 Those are used in RETURN FROM INTERRUPTION AND RESTORE instruction to reduce

102 the state save and restore time by eliminating the need for general register

103 (GR) saves and restores in interruption handlers.

104 Shadow registers are the GRs 1, 8, 9, 16, 17, 24, and 25.

105

106 -------------------------------------------------------------------------

107

108 Register usage notes, originally from John Marvin, with some additional

109 notes from Randolph Chung.

110

111 For the general registers:

112

113 r1,r2,r19-r26,r28,r29 & r31 can be used without saving them first. And of

114 course, you need to save them if you care about them, before calling

115 another procedure. Some of the above registers do have special meanings

116 that you should be aware of:

117

118 r1:

119 The addil instruction is hardwired to place its result in r1,

120 so if you use that instruction be aware of that.

121

122 r2:

123 This is the return pointer. In general you don't want to

124 use this, since you need the pointer to get back to your

125 caller. However, it is grouped with this set of registers

126 since the caller can't rely on the value being the same

127 when you return, i.e. you can copy r2 to another register

128 and return through that register after trashing r2, and

129 that should not cause a problem for the calling routine.

130

131 r19-r22:

132 these are generally regarded as temporary registers.

133 Note that in 64 bit they are arg7-arg4.

134

135 r23-r26:

136 these are arg3-arg0, i.e. you can use them if you

137 don't care about the values that were passed in anymore.

138

139 r28,r29:

140 are ret0 and ret1. They are what you pass return values

141 in. r28 is the primary return. When returning small structures

142 r29 may also be used to pass data back to the caller.

143

144 r30:

145 stack pointer

146

147 r31:

148 the ble instruction puts the return pointer in here.

149

150

151 r3-r18,r27,r30 need to be saved and restored. r3-r18 are just

152 general purpose registers. r27 is the data pointer, and is

153 used to make references to global variables easier. r30 is

154 the stack pointer.

155

3. 한국어 전문 번역

영어 원문의 문단 순서와 의미를 유지한 전체 번역입니다. 코드, 함수명, symbol과 URL은 원문 표기를 유지합니다.

ABI control register usage

1-38

이 문서는 Linux/PA-RISC register usage를 정리하며 asterisk는 계획됐지만 아직 구현되지 않은 사용을 뜻합니다.

Control register	Linux usage
`CR 0 (Recovery Counter)`	`used for ptrace`
`CR 1-CR 7(undefined)`	`unused`
`CR 8 (Protection ID)`	`per-process value*`
`CR 9, 12, 13 (PIDS)`	`unused`
`CR10 (CCR)`	`lazy FPU saving*`
`CR11`	`as specified by ABI (SAR)`
`CR14 (interruption vector)`	`initialized to fault_vector`
`CR15 (EIEM)`	`initialized to all ones*`
`CR16 (Interval Timer)`	`read for cycle count/write starts Interval Tmr`
`CR17-CR22`	`interruption parameters`
`CR19`	`Interrupt Instruction Register`
`CR20`	`Interrupt Space Register`
`CR21`	`Interrupt Offset Register`
`CR22`	`Interrupt PSW`
`CR23 (EIRR)`	`read for pending interrupts/write clears bits`
`CR24 (TR 0)`	`Kernel Space Page Directory Pointer`
`CR25 (TR 1)`	`User Space Page Directory Pointer`
`CR26 (TR 2)`	`not used`
`CR27 (TR 3)`	`Thread descriptor pointer`
`CR28 (TR 4)`	`not used`
`CR29 (TR 5)`	`not used`
`CR30 (TR 6)`	`current / 0`
`CR31 (TR 7)`	`Temporary register, used in various places`

Kernel/user space register

39-59

Kernel mode에서는 `SR3`가 현재 process의 userspace access에 쓰이고 `SR2`는 kernel이 보존해야 합니다. User mode에서는 `SR2`가 Linux gateway page space를, `SR3`가 kernel 진입 중 user address-space 값을 유지합니다.

Kernel-mode space register	Usage
`SR0`	`temporary space register`
`SR4-SR7`	`set to 0`
`SR1`	`temporary space register`
`SR2`	`kernel should not clobber this`
`SR3`	`used for userspace accesses (current process)`

User-mode space register	Usage
`SR0`	`temporary space register`
`SR1`	`temporary space register`
`SR2`	`holds space of linux gateway page`
`SR3`	`holds user address space value while in kernel`
`SR4-SR7`	`Defines short address space for user/kernel`

Processor Status Word

60-86

PSW field	Linux value/usage
`W (64-bit addresses)`	`0`
`E (Little-endian)`	`0`
`S (Secure Interval Timer)`	`0`
`T (Taken Branch Trap)`	`0`
`H (Higher-privilege trap)`	`0`
`L (Lower-privilege trap)`	`0`
`N (Nullify next instruction)`	`used by C code`
`X (Data memory break disable)`	`0`
`B (Taken Branch)`	`used by C code`
`C (code address translation)`	`1, 0 while executing real-mode code`
`V (divide step correction)`	`used by C code`
`M (HPMC mask)`	`0, 1 while executing HPMC handler*`
`C/B (carry/borrow bits)`	`used by C code`
`O (ordered references)`	`1*`
`F (performance monitor)`	`0`
`R (Recovery Counter trap)`	`0`
`Q (collect interruption state)`	`1 (0 in code directly preceding an rfi)`
`P (Protection Identifiers)`	`1*`
`D (Data address translation)`	`1, 0 while executing real-mode code`
`I (external interrupt mask)`	`used by cli()/sti() macros`

`C`와 `D` translation bit는 보통 1이지만 real-mode code에서는 0입니다. `Q`는 interruption state 수집을 위해 1이며 `rfi` 직전 code에서만 0입니다. External interrupt mask `I`는 `cli()/sti()` macro가 사용합니다.

Invisible/shadow register

87-106

Invisible register	Value/usage
`PSW default W value`	`0`
`PSW default E value`	`0`
`Shadow Registers`	`used by interruption handler code`
`TOC enable bit`	`1`

PA-RISC는 7개 shadow register를 정의합니다. `RETURN FROM INTERRUPTION AND RESTORE` instruction이 interruption handler의 general-register save/restore를 생략해 시간을 줄이는 데 사용합니다.

Shadow register는 원문 표기로 `GRs 1, 8, 9, 16, 17, 24, and 25`, 즉 general register `GR1`, `GR8`, `GR9`, `GR16`, `GR17`, `GR24`, `GR25`입니다.

Caller-clobbered general register

107-150

John Marvin의 원래 note와 Randolph Chung의 추가 note에 따르면 `r1`, `r2`, `r19-r26`, `r28`, `r29`, `r31`은 먼저 저장하지 않고 쓸 수 있습니다. 다만 다른 procedure를 call한 뒤 값이 필요하면 caller가 저장해야 합니다.

Register	특수 의미
`r1`	`addil` instruction 결과가 고정적으로 기록됨
`r2`	Return pointer. 다른 register로 복사해 그 register로 return할 수 있으며 callee 뒤 원래 값 보장은 없음
`r19-r22`	Temporary register, 64-bit에서는 `arg7-arg4`
`r23-r26`	`arg3-arg0`; 전달값이 더 필요 없을 때 사용 가능
`r28`, `r29`	`ret0`, `ret1`; `r28`이 primary return이고 small structure는 `r29`도 사용
`r30`	Stack pointer
`r31`	`ble` instruction이 return pointer를 기록

Callee-saved general register

151-154

`r3-r18`, `r27`, `r30`은 저장하고 복원해야 합니다. `r3-r18`은 general-purpose register이고 `r27`은 global-variable reference를 쉽게 하는 data pointer, `r30`은 stack pointer입니다.