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runtime: switch runtime to libc for openbsd/386

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Use libc rather than performing direct system calls for the runtime on
openbsd/386.

Updates #36435

Change-Id: I0cd65368bc824c81f5f98ea24e4f82db5468b170
Reviewed-on: https://go-review.googlesource.com/c/go/+/287653
Trust: Joel Sing <joel@sing.id.au>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
This commit is contained in:
Joel Sing
2021-01-28 23:43:33 +11:00
parent 0bbfc5c31e
commit faff49aae6
5 changed files with 364 additions and 278 deletions
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5
src/runtime/defs_openbsd_386.go
View File

@@ -32,6 +32,11 @@ const (
_PTHREAD_CREATE_DETACHED = 0x1
_F_SETFD = 0x2
_F_GETFL = 0x3
_F_SETFL = 0x4
_FD_CLOEXEC = 0x1
_SIGHUP = 0x1
_SIGINT = 0x2
_SIGQUIT = 0x3

4
src/runtime/os_openbsd_syscall2.go
View File

@@ -2,8 +2,8 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build openbsd && !amd64 && !arm64
// +build openbsd,!amd64,!arm64
//go:build openbsd && !386 && !amd64 && !arm64
// +build openbsd,!386,!amd64,!arm64
package runtime

2
src/runtime/proc.go
View File

@@ -1303,7 +1303,7 @@ func usesLibcall() bool {
case "aix", "darwin", "illumos", "ios", "solaris", "windows":
return true
case "openbsd":
return GOARCH == "amd64" || GOARCH == "arm64"
return GOARCH == "386" || GOARCH == "amd64" || GOARCH == "arm64"
}
return false
}

4
src/runtime/sys_openbsd2.go
View File

@@ -2,8 +2,8 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//go:build (openbsd && amd64) || (openbsd && arm64)
// +build openbsd,amd64 openbsd,arm64
//go:build (openbsd && 386) || (openbsd && amd64) || (openbsd && arm64)
// +build openbsd,386 openbsd,amd64 openbsd,arm64
package runtime

627
src/runtime/sys_openbsd_386.s
View File

@@ -169,6 +169,21 @@ TEXT runtime·pthread_create_trampoline(SB),NOSPLIT,$0
POPL BP
RET
TEXT runtime·thrkill_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
SUBL $12, SP
MOVL 20(SP), DX // pointer to args
MOVL 0(DX), AX
MOVL 4(DX), BX
MOVL AX, 0(SP) // arg 1 - tid
MOVL BX, 4(SP) // arg 2 - signal
MOVL $0, 8(SP) // arg 3 - tcb
CALL libc_thrkill(SB)
MOVL BP, SP
POPL BP
RET
TEXT runtime·thrsleep_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
@@ -203,6 +218,42 @@ TEXT runtime·thrwakeup_trampoline(SB),NOSPLIT,$0
POPL BP
RET
TEXT runtime·exit_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
SUBL $4, SP
MOVL 12(SP), DX // pointer to args
MOVL 0(DX), AX
MOVL AX, 0(SP) // arg 1 - status
CALL libc_exit(SB)
MOVL $0xf1, 0xf1 // crash on failure
MOVL BP, SP
POPL BP
RET
TEXT runtime·getthrid_trampoline(SB),NOSPLIT,$0
PUSHL BP
CALL libc_getthrid(SB)
NOP SP // tell vet SP changed - stop checking offsets
MOVL 8(SP), DX // pointer to return value
MOVL AX, 0(DX)
POPL BP
RET
TEXT runtime·raiseproc_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
SUBL $8, SP
MOVL 16(SP), DX
MOVL 0(DX), BX
CALL libc_getpid(SB)
MOVL AX, 0(SP) // arg 1 - pid
MOVL BX, 4(SP) // arg 2 - signal
CALL libc_kill(SB)
MOVL BP, SP
POPL BP
RET
TEXT runtime·sched_yield_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
@@ -211,308 +262,338 @@ TEXT runtime·sched_yield_trampoline(SB),NOSPLIT,$0
POPL BP
RET
// Exit the entire program (like C exit)
TEXT runtime·exit(SB),NOSPLIT,$-4
MOVL $1, AX
INT $0x80
MOVL $0xf1, 0xf1 // crash
RET
// func exitThread(wait *uint32)
TEXT runtime·exitThread(SB),NOSPLIT,$0-4
MOVL $302, AX // sys___threxit
INT $0x80
MOVL $0xf1, 0xf1 // crash
JMP 0(PC)
TEXT runtime·open(SB),NOSPLIT,$-4
MOVL $5, AX
INT $0x80
JAE 2(PC)
MOVL $-1, AX
MOVL AX, ret+12(FP)
RET
TEXT runtime·closefd(SB),NOSPLIT,$-4
MOVL $6, AX
INT $0x80
JAE 2(PC)
MOVL $-1, AX
MOVL AX, ret+4(FP)
RET
TEXT runtime·read(SB),NOSPLIT,$-4
MOVL $3, AX
INT $0x80
JAE 2(PC)
NEGL AX // caller expects negative errno
MOVL AX, ret+12(FP)
RET
// func pipe() (r, w int32, errno int32)
TEXT runtime·pipe(SB),NOSPLIT,$8-12
MOVL $263, AX
LEAL r+0(FP), BX
MOVL BX, 4(SP)
INT $0x80
MOVL AX, errno+8(FP)
RET
// func pipe2(flags int32) (r, w int32, errno int32)
TEXT runtime·pipe2(SB),NOSPLIT,$12-16
MOVL $101, AX
LEAL r+4(FP), BX
MOVL BX, 4(SP)
MOVL flags+0(FP), BX
MOVL BX, 8(SP)
INT $0x80
MOVL AX, errno+12(FP)
RET
TEXT runtime·write1(SB),NOSPLIT,$-4
MOVL $4, AX // sys_write
INT $0x80
JAE 2(PC)
NEGL AX // caller expects negative errno
MOVL AX, ret+12(FP)
RET
TEXT runtime·usleep(SB),NOSPLIT,$24
MOVL $0, DX
MOVL usec+0(FP), AX
MOVL $1000000, CX
DIVL CX
MOVL AX, 12(SP) // tv_sec - l32
MOVL $0, 16(SP) // tv_sec - h32
MOVL $1000, AX
MULL DX
MOVL AX, 20(SP) // tv_nsec
MOVL $0, 0(SP)
LEAL 12(SP), AX
MOVL AX, 4(SP) // arg 1 - rqtp
MOVL $0, 8(SP) // arg 2 - rmtp
MOVL $91, AX // sys_nanosleep
INT $0x80
RET
TEXT runtime·getthrid(SB),NOSPLIT,$0-4
MOVL $299, AX // sys_getthrid
INT $0x80
MOVL AX, ret+0(FP)
RET
TEXT runtime·thrkill(SB),NOSPLIT,$16-8
MOVL $0, 0(SP)
MOVL tid+0(FP), AX
MOVL AX, 4(SP) // arg 1 - tid
MOVL sig+4(FP), AX
MOVL AX, 8(SP) // arg 2 - signum
MOVL $0, 12(SP) // arg 3 - tcb
MOVL $119, AX // sys_thrkill
INT $0x80
RET
TEXT runtime·raiseproc(SB),NOSPLIT,$12
MOVL $20, AX // sys_getpid
INT $0x80
MOVL $0, 0(SP)
MOVL AX, 4(SP) // arg 1 - pid
MOVL sig+0(FP), AX
MOVL AX, 8(SP) // arg 2 - signum
MOVL $122, AX // sys_kill
INT $0x80
RET
TEXT runtime·mmap(SB),NOSPLIT,$36
LEAL addr+0(FP), SI
LEAL 4(SP), DI
CLD
MOVSL // arg 1 - addr
MOVSL // arg 2 - len
MOVSL // arg 3 - prot
MOVSL // arg 4 - flags
MOVSL // arg 5 - fd
TEXT runtime·mmap_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
SUBL $32, SP
MOVL 40(SP), DX // pointer to args
MOVL 0(DX), AX
MOVL 4(DX), BX
MOVL 8(DX), CX
MOVL AX, 0(SP) // arg 1 - addr
MOVL BX, 4(SP) // arg 2 - len
MOVL CX, 8(SP) // arg 3 - prot
MOVL 12(DX), AX
MOVL 16(DX), BX
MOVL 20(DX), CX
MOVL AX, 12(SP) // arg 4 - flags
MOVL BX, 16(SP) // arg 5 - fid
MOVL $0, 20(SP) // pad
MOVL CX, 24(SP) // arg 6 - offset (low 32 bits)
MOVL $0, 28(SP) // offset (high 32 bits)
CALL libc_mmap(SB)
MOVL $0, BX
CMPL AX, $-1
JNE ok
CALL libc_errno(SB)
MOVL (AX), BX
MOVL $0, AX
STOSL // arg 6 - pad
MOVSL // arg 7 - offset
MOVL $0, AX // top 32 bits of file offset
STOSL
MOVL $197, AX // sys_mmap
INT $0x80
JAE ok
MOVL $0, p+24(FP)
MOVL AX, err+28(FP)
RET
ok:
MOVL AX, p+24(FP)
MOVL $0, err+28(FP)
MOVL 40(SP), DX
MOVL AX, 24(DX)
MOVL BX, 28(DX)
MOVL BP, SP
POPL BP
RET
TEXT runtime·munmap(SB),NOSPLIT,$-4
MOVL $73, AX // sys_munmap
INT $0x80
JAE 2(PC)
MOVL $0xf1, 0xf1 // crash
TEXT runtime·munmap_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
SUBL $8, SP
MOVL 16(SP), DX // pointer to args
MOVL 0(DX), AX
MOVL 4(DX), BX
MOVL AX, 0(SP) // arg 1 - addr
MOVL BX, 4(SP) // arg 2 - len
CALL libc_munmap(SB)
CMPL AX, $-1
JNE 2(PC)
MOVL $0xf1, 0xf1 // crash on failure
MOVL BP, SP
POPL BP
RET
TEXT runtime·madvise(SB),NOSPLIT,$-4
MOVL $75, AX // sys_madvise
INT $0x80
JAE 2(PC)
MOVL $-1, AX
MOVL AX, ret+12(FP)
TEXT runtime·madvise_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
SUBL $12, SP
MOVL 20(SP), DX // pointer to args
MOVL 0(DX), AX
MOVL 4(DX), BX
MOVL 8(DX), CX
MOVL AX, 0(SP) // arg 1 - addr
MOVL BX, 4(SP) // arg 2 - len
MOVL CX, 8(SP) // arg 3 - advice
CALL libc_madvise(SB)
// ignore failure - maybe pages are locked
MOVL BP, SP
POPL BP
RET
TEXT runtime·setitimer(SB),NOSPLIT,$-4
MOVL $69, AX
INT $0x80
TEXT runtime·open_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
SUBL $16, SP
MOVL 24(SP), DX // pointer to args
MOVL 0(DX), AX
MOVL 4(DX), BX
MOVL 8(DX), CX
MOVL AX, 0(SP) // arg 1 - path
MOVL BX, 4(SP) // arg 2 - flags
MOVL CX, 8(SP) // arg 3 - mode
MOVL $0, 12(SP) // vararg
CALL libc_open(SB)
MOVL BP, SP
POPL BP
RET
// func walltime() (sec int64, nsec int32)
TEXT runtime·walltime(SB), NOSPLIT, $32
LEAL 12(SP), BX
MOVL $0, 4(SP) // arg 1 - clock_id
MOVL BX, 8(SP) // arg 2 - tp
MOVL $87, AX // sys_clock_gettime
INT $0x80
MOVL 12(SP), AX // sec - l32
MOVL AX, sec_lo+0(FP)
MOVL 16(SP), AX // sec - h32
MOVL AX, sec_hi+4(FP)
MOVL 20(SP), BX // nsec
MOVL BX, nsec+8(FP)
TEXT runtime·close_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
SUBL $4, SP
MOVL 12(SP), DX
MOVL 0(DX), AX
MOVL AX, 0(SP) // arg 1 - fd
CALL libc_close(SB)
MOVL BP, SP
POPL BP
RET
// int64 nanotime1(void) so really
// void nanotime1(int64 *nsec)
TEXT runtime·nanotime1(SB),NOSPLIT,$32
LEAL 12(SP), BX
MOVL CLOCK_MONOTONIC, 4(SP) // arg 1 - clock_id
MOVL BX, 8(SP) // arg 2 - tp
MOVL $87, AX // sys_clock_gettime
INT $0x80
MOVL 16(SP), CX // sec - h32
IMULL $1000000000, CX
MOVL 12(SP), AX // sec - l32
MOVL $1000000000, BX
MULL BX // result in dx:ax
MOVL 20(SP), BX // nsec
ADDL BX, AX
ADCL CX, DX // add high bits with carry
MOVL AX, ret_lo+0(FP)
MOVL DX, ret_hi+4(FP)
TEXT runtime·read_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
SUBL $12, SP
MOVL 20(SP), DX // pointer to args
MOVL 0(DX), AX
MOVL 4(DX), BX
MOVL 8(DX), CX
MOVL AX, 0(SP) // arg 1 - fd
MOVL BX, 4(SP) // arg 2 - buf
MOVL CX, 8(SP) // arg 3 - count
CALL libc_read(SB)
CMPL AX, $-1
JNE noerr
CALL libc_errno(SB)
MOVL (AX), AX
NEGL AX // caller expects negative errno
noerr:
MOVL BP, SP
POPL BP
RET
TEXT runtime·sigaction(SB),NOSPLIT,$-4
MOVL $46, AX // sys_sigaction
INT $0x80
JAE 2(PC)
MOVL $0xf1, 0xf1 // crash
TEXT runtime·write_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
SUBL $12, SP
MOVL 20(SP), DX // pointer to args
MOVL 0(DX), AX
MOVL 4(DX), BX
MOVL 8(DX), CX
MOVL AX, 0(SP) // arg 1 - fd
MOVL BX, 4(SP) // arg 2 - buf
MOVL CX, 8(SP) // arg 3 - count
CALL libc_write(SB)
CMPL AX, $-1
JNE noerr
CALL libc_errno(SB)
MOVL (AX), AX
NEGL AX // caller expects negative errno
noerr:
MOVL BP, SP
POPL BP
RET
TEXT runtime·obsdsigprocmask(SB),NOSPLIT,$-4
MOVL $48, AX // sys_sigprocmask
INT $0x80
JAE 2(PC)
MOVL $0xf1, 0xf1 // crash
MOVL AX, ret+8(FP)
TEXT runtime·pipe2_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
SUBL $8, SP
MOVL 16(SP), DX // pointer to args
MOVL 0(DX), AX
MOVL 4(DX), BX
MOVL AX, 0(SP) // arg 1 - fds
MOVL BX, 4(SP) // arg 2 - flags
CALL libc_pipe2(SB)
CMPL AX, $-1
JNE noerr
CALL libc_errno(SB)
MOVL (AX), AX
NEGL AX // caller expects negative errno
noerr:
MOVL BP, SP
POPL BP
RET
TEXT runtime·sigaltstack(SB),NOSPLIT,$-8
MOVL $288, AX // sys_sigaltstack
MOVL new+0(FP), BX
MOVL old+4(FP), CX
INT $0x80
CMPL AX, $0xfffff001
JLS 2(PC)
INT $3
TEXT runtime·setitimer_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
SUBL $12, SP
MOVL 20(SP), DX // pointer to args
MOVL 0(DX), AX
MOVL 4(DX), BX
MOVL 8(DX), CX
MOVL AX, 0(SP) // arg 1 - which
MOVL BX, 4(SP) // arg 2 - new
MOVL CX, 8(SP) // arg 3 - old
CALL libc_setitimer(SB)
MOVL BP, SP
POPL BP
RET
TEXT set_tcb<>(SB),NOSPLIT,$8
// adjust for ELF: wants to use -4(GS) for g
MOVL tlsbase+0(FP), CX
ADDL $4, CX
MOVL $0, 0(SP) // syscall gap
MOVL CX, 4(SP) // arg 1 - tcb
MOVL $329, AX // sys___set_tcb
INT $0x80
JCC 2(PC)
MOVL $0xf1, 0xf1 // crash
TEXT runtime·usleep_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
SUBL $4, SP
MOVL 12(SP), DX // pointer to args
MOVL 0(DX), AX
MOVL AX, 0(SP)
CALL libc_usleep(SB)
MOVL BP, SP
POPL BP
RET
TEXT runtime·sysctl(SB),NOSPLIT,$28
LEAL mib+0(FP), SI
LEAL 4(SP), DI
CLD
MOVSL // arg 1 - name
MOVSL // arg 2 - namelen
MOVSL // arg 3 - oldp
MOVSL // arg 4 - oldlenp
MOVSL // arg 5 - newp
MOVSL // arg 6 - newlen
MOVL $202, AX // sys___sysctl
INT $0x80
JCC 4(PC)
NEGL AX
MOVL AX, ret+24(FP)
RET
MOVL $0, AX
MOVL AX, ret+24(FP)
TEXT runtime·sysctl_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
SUBL $24, SP
MOVL 32(SP), DX // pointer to args
MOVL 0(DX), AX
MOVL 4(DX), BX
MOVL 8(DX), CX
MOVL AX, 0(SP) // arg 1 - name
MOVL BX, 4(SP) // arg 2 - namelen
MOVL CX, 8(SP) // arg 3 - old
MOVL 12(DX), AX
MOVL 16(DX), BX
MOVL 20(DX), CX
MOVL AX, 12(SP) // arg 4 - oldlenp
MOVL BX, 16(SP) // arg 5 - newp
MOVL CX, 20(SP) // arg 6 - newlen
CALL libc_sysctl(SB)
MOVL BP, SP
POPL BP
RET
// int32 runtime·kqueue(void);
TEXT runtime·kqueue(SB),NOSPLIT,$0
MOVL $269, AX
INT $0x80
JAE 2(PC)
NEGL AX
MOVL AX, ret+0(FP)
TEXT runtime·kqueue_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
CALL libc_kqueue(SB)
MOVL BP, SP
POPL BP
RET
// int32 runtime·kevent(int kq, Kevent *changelist, int nchanges, Kevent *eventlist, int nevents, Timespec *timeout);
TEXT runtime·kevent(SB),NOSPLIT,$0
MOVL $72, AX // sys_kevent
INT $0x80
JAE 2(PC)
NEGL AX
MOVL AX, ret+24(FP)
TEXT runtime·kevent_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
SUBL $24, SP
MOVL 32(SP), DX // pointer to args
MOVL 0(DX), AX
MOVL 4(DX), BX
MOVL 8(DX), CX
MOVL AX, 0(SP) // arg 1 - kq
MOVL BX, 4(SP) // arg 2 - keventt
MOVL CX, 8(SP) // arg 3 - nch
MOVL 12(DX), AX
MOVL 16(DX), BX
MOVL 20(DX), CX
MOVL AX, 12(SP) // arg 4 - ev
MOVL BX, 16(SP) // arg 5 - nev
MOVL CX, 20(SP) // arg 6 - ts
CALL libc_kevent(SB)
CMPL AX, $-1
JNE noerr
CALL libc_errno(SB)
MOVL (AX), AX
NEGL AX // caller expects negative errno
noerr:
MOVL BP, SP
POPL BP
RET
// int32 runtime·closeonexec(int32 fd);
TEXT runtime·closeonexec(SB),NOSPLIT,$32
MOVL $92, AX // sys_fcntl
// 0(SP) is where the caller PC would be; kernel skips it
MOVL fd+0(FP), BX
MOVL BX, 4(SP) // fd
MOVL $2, 8(SP) // F_SETFD
MOVL $1, 12(SP) // FD_CLOEXEC
INT $0x80
JAE 2(PC)
NEGL AX
TEXT runtime·clock_gettime_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
SUBL $8, SP
MOVL 16(SP), DX // pointer to args
MOVL 0(DX), AX
MOVL 4(DX), BX
MOVL AX, 0(SP) // arg 1 - tp
MOVL BX, 4(SP) // arg 2 - clock_id
CALL libc_clock_gettime(SB)
CMPL AX, $-1
JNE 2(PC)
MOVL $0xf1, 0xf1 // crash on failure
MOVL BP, SP
POPL BP
RET
// func runtime·setNonblock(fd int32)
TEXT runtime·setNonblock(SB),NOSPLIT,$16-4
MOVL $92, AX // fcntl
MOVL fd+0(FP), BX // fd
MOVL BX, 4(SP)
MOVL $3, 8(SP) // F_GETFL
MOVL $0, 12(SP)
INT $0x80
MOVL fd+0(FP), BX // fd
MOVL BX, 4(SP)
MOVL $4, 8(SP) // F_SETFL
ORL $4, AX // O_NONBLOCK
MOVL AX, 12(SP)
MOVL $92, AX // fcntl
INT $0x80
TEXT runtime·fcntl_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
SUBL $16, SP
MOVL 24(SP), DX // pointer to args
MOVL 0(DX), AX
MOVL 4(DX), BX
MOVL 8(DX), CX
MOVL AX, 0(SP) // arg 1 - fd
MOVL BX, 4(SP) // arg 2 - cmd
MOVL CX, 8(SP) // arg 3 - arg
MOVL $0, 12(SP) // vararg
CALL libc_fcntl(SB)
MOVL BP, SP
POPL BP
RET
GLOBL runtime·tlsoffset(SB),NOPTR,$4
TEXT runtime·sigaction_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
SUBL $12, SP
MOVL 20(SP), DX // pointer to args
MOVL 0(DX), AX
MOVL 4(DX), BX
MOVL 8(DX), CX
MOVL AX, 0(SP) // arg 1 - sig
MOVL BX, 4(SP) // arg 2 - new
MOVL CX, 8(SP) // arg 3 - old
CALL libc_sigaction(SB)
CMPL AX, $-1
JNE 2(PC)
MOVL $0xf1, 0xf1 // crash on failure
MOVL BP, SP
POPL BP
RET
TEXT runtime·sigprocmask_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
SUBL $12, SP
MOVL 20(SP), DX // pointer to args
MOVL 0(DX), AX
MOVL 4(DX), BX
MOVL 8(DX), CX
MOVL AX, 0(SP) // arg 1 - how
MOVL BX, 4(SP) // arg 2 - new
MOVL CX, 8(SP) // arg 3 - old
CALL libc_pthread_sigmask(SB)
CMPL AX, $-1
JNE 2(PC)
MOVL $0xf1, 0xf1 // crash on failure
MOVL BP, SP
POPL BP
RET
TEXT runtime·sigaltstack_trampoline(SB),NOSPLIT,$0
PUSHL BP
MOVL SP, BP
SUBL $8, SP
MOVL 16(SP), DX // pointer to args
MOVL 0(DX), AX
MOVL 4(DX), BX
MOVL AX, 0(SP) // arg 1 - new
MOVL BX, 4(SP) // arg 2 - old
CALL libc_sigaltstack(SB)
CMPL AX, $-1
JNE 2(PC)
MOVL $0xf1, 0xf1 // crash on failure
MOVL BP, SP
POPL BP
RET