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linux/arch/alpha/kernel/entry.S

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/* SPDX-License-Identifier: GPL-2.0 */
/*
* arch/alpha/kernel/entry.S
*
* Kernel entry-points.
*/
#include <asm/asm-offsets.h>
#include <asm/thread_info.h>
#include <asm/pal.h>
#include <asm/errno.h>
#include <asm/unistd.h>
.text
.set noat
.cfi_sections .debug_frame
/* Stack offsets. */
#define SP_OFF 184
#define SWITCH_STACK_SIZE 320
.macro CFI_START_OSF_FRAME func
.align 4
.globl \func
.type \func,@function
\func:
.cfi_startproc simple
.cfi_return_column 64
.cfi_def_cfa $sp, 48
.cfi_rel_offset 64, 8
.cfi_rel_offset $gp, 16
.cfi_rel_offset $16, 24
.cfi_rel_offset $17, 32
.cfi_rel_offset $18, 40
.endm
.macro CFI_END_OSF_FRAME func
.cfi_endproc
.size \func, . - \func
.endm
/*
* This defines the normal kernel pt-regs layout.
*
* regs 9-15 preserved by C code
* regs 16-18 saved by PAL-code
* regs 29-30 saved and set up by PAL-code
* JRP - Save regs 16-18 in a special area of the stack, so that
* the palcode-provided values are available to the signal handler.
*/
.macro SAVE_ALL
subq $sp, SP_OFF, $sp
.cfi_adjust_cfa_offset SP_OFF
stq $0, 0($sp)
stq $1, 8($sp)
stq $2, 16($sp)
stq $3, 24($sp)
stq $4, 32($sp)
stq $28, 144($sp)
.cfi_rel_offset $0, 0
.cfi_rel_offset $1, 8
.cfi_rel_offset $2, 16
.cfi_rel_offset $3, 24
.cfi_rel_offset $4, 32
.cfi_rel_offset $28, 144
lda $2, alpha_mv
stq $5, 40($sp)
stq $6, 48($sp)
stq $7, 56($sp)
stq $8, 64($sp)
stq $19, 72($sp)
stq $20, 80($sp)
stq $21, 88($sp)
ldq $2, HAE_CACHE($2)
stq $22, 96($sp)
stq $23, 104($sp)
stq $24, 112($sp)
stq $25, 120($sp)
stq $26, 128($sp)
stq $27, 136($sp)
stq $2, 152($sp)
stq $16, 160($sp)
stq $17, 168($sp)
stq $18, 176($sp)
.cfi_rel_offset $5, 40
.cfi_rel_offset $6, 48
.cfi_rel_offset $7, 56
.cfi_rel_offset $8, 64
.cfi_rel_offset $19, 72
.cfi_rel_offset $20, 80
.cfi_rel_offset $21, 88
.cfi_rel_offset $22, 96
.cfi_rel_offset $23, 104
.cfi_rel_offset $24, 112
.cfi_rel_offset $25, 120
.cfi_rel_offset $26, 128
.cfi_rel_offset $27, 136
.endm
.macro RESTORE_ALL
lda $19, alpha_mv
ldq $0, 0($sp)
ldq $1, 8($sp)
ldq $2, 16($sp)
ldq $3, 24($sp)
ldq $21, 152($sp)
ldq $20, HAE_CACHE($19)
ldq $4, 32($sp)
ldq $5, 40($sp)
ldq $6, 48($sp)
ldq $7, 56($sp)
subq $20, $21, $20
ldq $8, 64($sp)
beq $20, 99f
ldq $20, HAE_REG($19)
stq $21, HAE_CACHE($19)
stq $21, 0($20)
99: ldq $19, 72($sp)
ldq $20, 80($sp)
ldq $21, 88($sp)
ldq $22, 96($sp)
ldq $23, 104($sp)
ldq $24, 112($sp)
ldq $25, 120($sp)
ldq $26, 128($sp)
ldq $27, 136($sp)
ldq $28, 144($sp)
addq $sp, SP_OFF, $sp
.cfi_restore $0
.cfi_restore $1
.cfi_restore $2
.cfi_restore $3
.cfi_restore $4
.cfi_restore $5
.cfi_restore $6
.cfi_restore $7
.cfi_restore $8
.cfi_restore $19
.cfi_restore $20
.cfi_restore $21
.cfi_restore $22
.cfi_restore $23
.cfi_restore $24
.cfi_restore $25
.cfi_restore $26
.cfi_restore $27
.cfi_restore $28
.cfi_adjust_cfa_offset -SP_OFF
.endm
.macro DO_SWITCH_STACK
bsr $1, do_switch_stack
.cfi_adjust_cfa_offset SWITCH_STACK_SIZE
.cfi_rel_offset $9, 0
.cfi_rel_offset $10, 8
.cfi_rel_offset $11, 16
.cfi_rel_offset $12, 24
.cfi_rel_offset $13, 32
.cfi_rel_offset $14, 40
.cfi_rel_offset $15, 48
/* We don't really care about the FP registers for debugging. */
.endm
.macro UNDO_SWITCH_STACK
bsr $1, undo_switch_stack
.cfi_restore $9
.cfi_restore $10
.cfi_restore $11
.cfi_restore $12
.cfi_restore $13
.cfi_restore $14
.cfi_restore $15
.cfi_adjust_cfa_offset -SWITCH_STACK_SIZE
.endm
/*
* Non-syscall kernel entry points.
*/
CFI_START_OSF_FRAME entInt
SAVE_ALL
lda $8, 0x3fff
lda $26, ret_from_sys_call
bic $sp, $8, $8
mov $sp, $19
jsr $31, do_entInt
CFI_END_OSF_FRAME entInt
CFI_START_OSF_FRAME entArith
SAVE_ALL
lda $8, 0x3fff
lda $26, ret_from_sys_call
bic $sp, $8, $8
mov $sp, $18
jsr $31, do_entArith
CFI_END_OSF_FRAME entArith
CFI_START_OSF_FRAME entMM
SAVE_ALL
/* save $9 - $15 so the inline exception code can manipulate them. */
subq $sp, 56, $sp
.cfi_adjust_cfa_offset 56
stq $9, 0($sp)
stq $10, 8($sp)
stq $11, 16($sp)
stq $12, 24($sp)
stq $13, 32($sp)
stq $14, 40($sp)
stq $15, 48($sp)
.cfi_rel_offset $9, 0
.cfi_rel_offset $10, 8
.cfi_rel_offset $11, 16
.cfi_rel_offset $12, 24
.cfi_rel_offset $13, 32
.cfi_rel_offset $14, 40
.cfi_rel_offset $15, 48
addq $sp, 56, $19
/* handle the fault */
lda $8, 0x3fff
bic $sp, $8, $8
jsr $26, do_page_fault
/* reload the registers after the exception code played. */
ldq $9, 0($sp)
ldq $10, 8($sp)
ldq $11, 16($sp)
ldq $12, 24($sp)
ldq $13, 32($sp)
ldq $14, 40($sp)
ldq $15, 48($sp)
addq $sp, 56, $sp
.cfi_restore $9
.cfi_restore $10
.cfi_restore $11
.cfi_restore $12
.cfi_restore $13
.cfi_restore $14
.cfi_restore $15
.cfi_adjust_cfa_offset -56
/* finish up the syscall as normal. */
br ret_from_sys_call
CFI_END_OSF_FRAME entMM
CFI_START_OSF_FRAME entIF
SAVE_ALL
lda $8, 0x3fff
lda $26, ret_from_sys_call
bic $sp, $8, $8
mov $sp, $17
jsr $31, do_entIF
CFI_END_OSF_FRAME entIF
CFI_START_OSF_FRAME entUna
lda $sp, -256($sp)
.cfi_adjust_cfa_offset 256
stq $0, 0($sp)
.cfi_rel_offset $0, 0
.cfi_remember_state
ldq $0, 256($sp) /* get PS */
stq $1, 8($sp)
stq $2, 16($sp)
stq $3, 24($sp)
and $0, 8, $0 /* user mode? */
stq $4, 32($sp)
bne $0, entUnaUser /* yup -> do user-level unaligned fault */
stq $5, 40($sp)
stq $6, 48($sp)
stq $7, 56($sp)
stq $8, 64($sp)
stq $9, 72($sp)
stq $10, 80($sp)
stq $11, 88($sp)
stq $12, 96($sp)
stq $13, 104($sp)
stq $14, 112($sp)
stq $15, 120($sp)
/* 16-18 PAL-saved */
stq $19, 152($sp)
stq $20, 160($sp)
stq $21, 168($sp)
stq $22, 176($sp)
stq $23, 184($sp)
stq $24, 192($sp)
stq $25, 200($sp)
stq $26, 208($sp)
stq $27, 216($sp)
stq $28, 224($sp)
mov $sp, $19
stq $gp, 232($sp)
.cfi_rel_offset $1, 1*8
.cfi_rel_offset $2, 2*8
.cfi_rel_offset $3, 3*8
.cfi_rel_offset $4, 4*8
.cfi_rel_offset $5, 5*8
.cfi_rel_offset $6, 6*8
.cfi_rel_offset $7, 7*8
.cfi_rel_offset $8, 8*8
.cfi_rel_offset $9, 9*8
.cfi_rel_offset $10, 10*8
.cfi_rel_offset $11, 11*8
.cfi_rel_offset $12, 12*8
.cfi_rel_offset $13, 13*8
.cfi_rel_offset $14, 14*8
.cfi_rel_offset $15, 15*8
.cfi_rel_offset $19, 19*8
.cfi_rel_offset $20, 20*8
.cfi_rel_offset $21, 21*8
.cfi_rel_offset $22, 22*8
.cfi_rel_offset $23, 23*8
.cfi_rel_offset $24, 24*8
.cfi_rel_offset $25, 25*8
.cfi_rel_offset $26, 26*8
.cfi_rel_offset $27, 27*8
.cfi_rel_offset $28, 28*8
.cfi_rel_offset $29, 29*8
lda $8, 0x3fff
stq $31, 248($sp)
bic $sp, $8, $8
jsr $26, do_entUna
ldq $0, 0($sp)
ldq $1, 8($sp)
ldq $2, 16($sp)
ldq $3, 24($sp)
ldq $4, 32($sp)
ldq $5, 40($sp)
ldq $6, 48($sp)
ldq $7, 56($sp)
ldq $8, 64($sp)
ldq $9, 72($sp)
ldq $10, 80($sp)
ldq $11, 88($sp)
ldq $12, 96($sp)
ldq $13, 104($sp)
ldq $14, 112($sp)
ldq $15, 120($sp)
/* 16-18 PAL-saved */
ldq $19, 152($sp)
ldq $20, 160($sp)
ldq $21, 168($sp)
ldq $22, 176($sp)
ldq $23, 184($sp)
ldq $24, 192($sp)
ldq $25, 200($sp)
ldq $26, 208($sp)
ldq $27, 216($sp)
ldq $28, 224($sp)
ldq $gp, 232($sp)
lda $sp, 256($sp)
.cfi_restore $1
.cfi_restore $2
.cfi_restore $3
.cfi_restore $4
.cfi_restore $5
.cfi_restore $6
.cfi_restore $7
.cfi_restore $8
.cfi_restore $9
.cfi_restore $10
.cfi_restore $11
.cfi_restore $12
.cfi_restore $13
.cfi_restore $14
.cfi_restore $15
.cfi_restore $19
.cfi_restore $20
.cfi_restore $21
.cfi_restore $22
.cfi_restore $23
.cfi_restore $24
.cfi_restore $25
.cfi_restore $26
.cfi_restore $27
.cfi_restore $28
.cfi_restore $29
.cfi_adjust_cfa_offset -256
call_pal PAL_rti
.align 4
entUnaUser:
.cfi_restore_state
ldq $0, 0($sp) /* restore original $0 */
lda $sp, 256($sp) /* pop entUna's stack frame */
.cfi_restore $0
.cfi_adjust_cfa_offset -256
SAVE_ALL /* setup normal kernel stack */
lda $sp, -56($sp)
.cfi_adjust_cfa_offset 56
stq $9, 0($sp)
stq $10, 8($sp)
stq $11, 16($sp)
stq $12, 24($sp)
stq $13, 32($sp)
stq $14, 40($sp)
stq $15, 48($sp)
.cfi_rel_offset $9, 0
.cfi_rel_offset $10, 8
.cfi_rel_offset $11, 16
.cfi_rel_offset $12, 24
.cfi_rel_offset $13, 32
.cfi_rel_offset $14, 40
.cfi_rel_offset $15, 48
lda $8, 0x3fff
addq $sp, 56, $19
bic $sp, $8, $8
jsr $26, do_entUnaUser
ldq $9, 0($sp)
ldq $10, 8($sp)
ldq $11, 16($sp)
ldq $12, 24($sp)
ldq $13, 32($sp)
ldq $14, 40($sp)
ldq $15, 48($sp)
lda $sp, 56($sp)
.cfi_restore $9
.cfi_restore $10
.cfi_restore $11
.cfi_restore $12
.cfi_restore $13
.cfi_restore $14
.cfi_restore $15
.cfi_adjust_cfa_offset -56
br ret_from_sys_call
CFI_END_OSF_FRAME entUna
CFI_START_OSF_FRAME entDbg
SAVE_ALL
lda $8, 0x3fff
lda $26, ret_from_sys_call
bic $sp, $8, $8
mov $sp, $16
jsr $31, do_entDbg
CFI_END_OSF_FRAME entDbg
/*
* The system call entry point is special. Most importantly, it looks
* like a function call to userspace as far as clobbered registers. We
* do preserve the argument registers (for syscall restarts) and $26
* (for leaf syscall functions).
*
* So much for theory. We don't take advantage of this yet.
*
* Note that a0-a2 are not saved by PALcode as with the other entry points.
*/
.align 4
.globl entSys
.type entSys, @function
.cfi_startproc simple
.cfi_return_column 64
.cfi_def_cfa $sp, 48
.cfi_rel_offset 64, 8
.cfi_rel_offset $gp, 16
entSys:
SAVE_ALL
lda $8, 0x3fff
bic $sp, $8, $8
lda $4, NR_SYSCALLS($31)
stq $16, SP_OFF+24($sp)
lda $5, sys_call_table
lda $27, sys_ni_syscall
cmpult $0, $4, $4
ldl $3, TI_FLAGS($8)
stq $17, SP_OFF+32($sp)
s8addq $0, $5, $5
stq $18, SP_OFF+40($sp)
.cfi_rel_offset $16, SP_OFF+24
.cfi_rel_offset $17, SP_OFF+32
.cfi_rel_offset $18, SP_OFF+40
#ifdef CONFIG_AUDITSYSCALL
lda $6, _TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT
and $3, $6, $3
#endif
bne $3, strace
beq $4, 1f
ldq $27, 0($5)
1: jsr $26, ($27), sys_ni_syscall
ldgp $gp, 0($26)
blt $0, $syscall_error /* the call failed */
stq $0, 0($sp)
stq $31, 72($sp) /* a3=0 => no error */
.align 4
.globl ret_from_sys_call
ret_from_sys_call:
cmovne $26, 0, $18 /* $18 = 0 => non-restartable */
ldq $0, SP_OFF($sp)
and $0, 8, $0
beq $0, ret_to_kernel
ret_to_user:
/* Make sure need_resched and sigpending don't change between
sampling and the rti. */
lda $16, 7
call_pal PAL_swpipl
ldl $17, TI_FLAGS($8)
and $17, _TIF_WORK_MASK, $2
bne $2, work_pending
restore_all:
.cfi_remember_state
RESTORE_ALL
call_pal PAL_rti
ret_to_kernel:
.cfi_restore_state
lda $16, 7
call_pal PAL_swpipl
br restore_all
.align 3
$syscall_error:
/*
* Some system calls (e.g., ptrace) can return arbitrary
* values which might normally be mistaken as error numbers.
* Those functions must zero $0 (v0) directly in the stack
* frame to indicate that a negative return value wasn't an
* error number..
*/
ldq $18, 0($sp) /* old syscall nr (zero if success) */
beq $18, $ret_success
ldq $19, 72($sp) /* .. and this a3 */
subq $31, $0, $0 /* with error in v0 */
addq $31, 1, $1 /* set a3 for errno return */
stq $0, 0($sp)
mov $31, $26 /* tell "ret_from_sys_call" we can restart */
stq $1, 72($sp) /* a3 for return */
br ret_from_sys_call
$ret_success:
stq $0, 0($sp)
stq $31, 72($sp) /* a3=0 => no error */
br ret_from_sys_call
/*
* Do all cleanup when returning from all interrupts and system calls.
*
* Arguments:
* $8: current.
* $17: TI_FLAGS.
* $18: The old syscall number, or zero if this is not a return
* from a syscall that errored and is possibly restartable.
* $19: The old a3 value
*/
.align 4
.type work_pending, @function
work_pending:
and $17, _TIF_NOTIFY_RESUME | _TIF_SIGPENDING, $2
bne $2, $work_notifysig
$work_resched:
/*
* We can get here only if we returned from syscall without SIGPENDING
* or got through work_notifysig already. Either case means no syscall
* restarts for us, so let $18 and $19 burn.
*/
jsr $26, schedule
mov 0, $18
br ret_to_user
$work_notifysig:
mov $sp, $16
DO_SWITCH_STACK
jsr $26, do_work_pending
UNDO_SWITCH_STACK
br restore_all
/*
* PTRACE syscall handler
*/
.align 4
.type strace, @function
strace:
/* set up signal stack, call syscall_trace */
DO_SWITCH_STACK
jsr $26, syscall_trace_enter /* returns the syscall number */
UNDO_SWITCH_STACK
/* get the arguments back.. */
ldq $16, SP_OFF+24($sp)
ldq $17, SP_OFF+32($sp)
ldq $18, SP_OFF+40($sp)
ldq $19, 72($sp)
ldq $20, 80($sp)
ldq $21, 88($sp)
/* get the system call pointer.. */
lda $1, NR_SYSCALLS($31)
lda $2, sys_call_table
lda $27, sys_ni_syscall
cmpult $0, $1, $1
s8addq $0, $2, $2
beq $1, 1f
ldq $27, 0($2)
1: jsr $26, ($27), sys_gettimeofday
ret_from_straced:
ldgp $gp, 0($26)
/* check return.. */
blt $0, $strace_error /* the call failed */
stq $31, 72($sp) /* a3=0 => no error */
$strace_success:
stq $0, 0($sp) /* save return value */
DO_SWITCH_STACK
jsr $26, syscall_trace_leave
UNDO_SWITCH_STACK
br $31, ret_from_sys_call
.align 3
$strace_error:
ldq $18, 0($sp) /* old syscall nr (zero if success) */
beq $18, $strace_success
ldq $19, 72($sp) /* .. and this a3 */
subq $31, $0, $0 /* with error in v0 */
addq $31, 1, $1 /* set a3 for errno return */
stq $0, 0($sp)
stq $1, 72($sp) /* a3 for return */
DO_SWITCH_STACK
mov $18, $9 /* save old syscall number */
mov $19, $10 /* save old a3 */
jsr $26, syscall_trace_leave
mov $9, $18
mov $10, $19
UNDO_SWITCH_STACK
mov $31, $26 /* tell "ret_from_sys_call" we can restart */
br ret_from_sys_call
CFI_END_OSF_FRAME entSys
/*
* Save and restore the switch stack -- aka the balance of the user context.
*/
.align 4
.type do_switch_stack, @function
.cfi_startproc simple
.cfi_return_column 64
.cfi_def_cfa $sp, 0
.cfi_register 64, $1
do_switch_stack:
lda $sp, -SWITCH_STACK_SIZE($sp)
.cfi_adjust_cfa_offset SWITCH_STACK_SIZE
stq $9, 0($sp)
stq $10, 8($sp)
stq $11, 16($sp)
stq $12, 24($sp)
stq $13, 32($sp)
stq $14, 40($sp)
stq $15, 48($sp)
stq $26, 56($sp)
stt $f0, 64($sp)
stt $f1, 72($sp)
stt $f2, 80($sp)
stt $f3, 88($sp)
stt $f4, 96($sp)
stt $f5, 104($sp)
stt $f6, 112($sp)
stt $f7, 120($sp)
stt $f8, 128($sp)
stt $f9, 136($sp)
stt $f10, 144($sp)
stt $f11, 152($sp)
stt $f12, 160($sp)
stt $f13, 168($sp)
stt $f14, 176($sp)
stt $f15, 184($sp)
stt $f16, 192($sp)
stt $f17, 200($sp)
stt $f18, 208($sp)
stt $f19, 216($sp)
stt $f20, 224($sp)
stt $f21, 232($sp)
stt $f22, 240($sp)
stt $f23, 248($sp)
stt $f24, 256($sp)
stt $f25, 264($sp)
stt $f26, 272($sp)
stt $f27, 280($sp)
mf_fpcr $f0 # get fpcr
stt $f28, 288($sp)
stt $f29, 296($sp)
stt $f30, 304($sp)
stt $f0, 312($sp) # save fpcr in slot of $f31
ldt $f0, 64($sp) # dont let "do_switch_stack" change fp state.
ret $31, ($1), 1
.cfi_endproc
.size do_switch_stack, .-do_switch_stack
.align 4
.type undo_switch_stack, @function
.cfi_startproc simple
.cfi_def_cfa $sp, 0
.cfi_register 64, $1
undo_switch_stack:
ldq $9, 0($sp)
ldq $10, 8($sp)
ldq $11, 16($sp)
ldq $12, 24($sp)
ldq $13, 32($sp)
ldq $14, 40($sp)
ldq $15, 48($sp)
ldq $26, 56($sp)
ldt $f30, 312($sp) # get saved fpcr
ldt $f0, 64($sp)
ldt $f1, 72($sp)
ldt $f2, 80($sp)
ldt $f3, 88($sp)
mt_fpcr $f30 # install saved fpcr
ldt $f4, 96($sp)
ldt $f5, 104($sp)
ldt $f6, 112($sp)
ldt $f7, 120($sp)
ldt $f8, 128($sp)
ldt $f9, 136($sp)
ldt $f10, 144($sp)
ldt $f11, 152($sp)
ldt $f12, 160($sp)
ldt $f13, 168($sp)
ldt $f14, 176($sp)
ldt $f15, 184($sp)
ldt $f16, 192($sp)
ldt $f17, 200($sp)
ldt $f18, 208($sp)
ldt $f19, 216($sp)
ldt $f20, 224($sp)
ldt $f21, 232($sp)
ldt $f22, 240($sp)
ldt $f23, 248($sp)
ldt $f24, 256($sp)
ldt $f25, 264($sp)
ldt $f26, 272($sp)
ldt $f27, 280($sp)
ldt $f28, 288($sp)
ldt $f29, 296($sp)
ldt $f30, 304($sp)
lda $sp, SWITCH_STACK_SIZE($sp)
ret $31, ($1), 1
.cfi_endproc
.size undo_switch_stack, .-undo_switch_stack
/*
* The meat of the context switch code.
*/
.align 4
.globl alpha_switch_to
.type alpha_switch_to, @function
.cfi_startproc
alpha_switch_to:
DO_SWITCH_STACK
call_pal PAL_swpctx
lda $8, 0x3fff
UNDO_SWITCH_STACK
bic $sp, $8, $8
mov $17, $0
ret
.cfi_endproc
.size alpha_switch_to, .-alpha_switch_to
/*
* New processes begin life here.
*/
.globl ret_from_fork
.align 4
.ent ret_from_fork
ret_from_fork:
lda $26, ret_from_sys_call
mov $17, $16
jmp $31, schedule_tail
.end ret_from_fork
/*
* ... and new kernel threads - here
*/
.align 4
.globl ret_from_kernel_thread
.ent ret_from_kernel_thread
ret_from_kernel_thread:
mov $17, $16
jsr $26, schedule_tail
mov $9, $27
mov $10, $16
jsr $26, ($9)
br $31, ret_to_user
.end ret_from_kernel_thread
/*
* Special system calls. Most of these are special in that they either
* have to play switch_stack games.
*/
.macro fork_like name
.align 4
.globl alpha_\name
.ent alpha_\name
alpha_\name:
.prologue 0
bsr $1, do_switch_stack
jsr $26, sys_\name
ldq $26, 56($sp)
lda $sp, SWITCH_STACK_SIZE($sp)
ret
.end alpha_\name
.endm
fork_like fork
fork_like vfork
fork_like clone
.macro sigreturn_like name
.align 4
.globl sys_\name
.ent sys_\name
sys_\name:
.prologue 0
lda $9, ret_from_straced
cmpult $26, $9, $9
lda $sp, -SWITCH_STACK_SIZE($sp)
jsr $26, do_\name
bne $9, 1f
jsr $26, syscall_trace_leave
1: br $1, undo_switch_stack
br ret_from_sys_call
.end sys_\name
.endm
sigreturn_like sigreturn
sigreturn_like rt_sigreturn
.align 4
.globl alpha_syscall_zero
.ent alpha_syscall_zero
alpha_syscall_zero:
.prologue 0
/* Special because it needs to do something opposite to
force_successful_syscall_return(). We use the saved
syscall number for that, zero meaning "not an error".
That works nicely, but for real syscall 0 we need to
make sure that this logics doesn't get confused.
Store a non-zero there - -ENOSYS we need in register
for our return value will do just fine.
*/
lda $0, -ENOSYS
unop
stq $0, 0($sp)
ret
.end alpha_syscall_zero
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