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| Commit | Line | Data |
|---|---|---|
| e6817382 BJ |
1 | .TH INDIR 2 |
| 2 | .SH NAME | |
| 3 | indir, syscall \- indirect system call | |
| 4 | .SH SYNOPSIS | |
| 5 | .BR "syscall(number, r0, r1, arg ...)" \ \ (PDP-11) | |
| 6 | .br | |
| 7 | .BR "syscall(number, arg, ...)" \ \ (VAX-11) | |
| 8 | .SH DESCRIPTION | |
| 9 | .I Syscall | |
| 10 | performs the system call whose assembly language | |
| 11 | interface has the specified | |
| 12 | .I number, | |
| 13 | register arguments | |
| 14 | .I r0 | |
| 15 | and | |
| 16 | .I r1 | |
| 17 | (on the PDP-11, regardless of whether the entry point really | |
| 18 | uses them) and further arguments | |
| 19 | .IR arg . | |
| 20 | .PP | |
| 21 | The r0 value of the system call is returned. | |
| 22 | .SH DIAGNOSTICS | |
| 23 | When the C-bit is set, | |
| 24 | .I syscall | |
| 25 | returns \-1 and sets the | |
| 26 | external variable | |
| 27 | .I errno | |
| 28 | (see | |
| 29 | .IR intro (2)). | |
| 30 | .SH BUGS | |
| 31 | There is no way to simulate system calls | |
| 32 | such as | |
| 33 | .IR pipe (2), | |
| 34 | which return values in register r1. | |
| 35 | .SH "ASSEMBLER (PDP-11)" | |
| 36 | (indir = 0.) | |
| 37 | .br | |
| 38 | .B sys indir; call | |
| 39 | .PP | |
| 40 | The system call at the location | |
| 41 | .I call | |
| 42 | is executed. | |
| 43 | Execution resumes after the | |
| 44 | .I indir | |
| 45 | call. | |
| 46 | .PP | |
| 47 | On the PDP-11, the main purpose of | |
| 48 | .I indir | |
| 49 | is to allow a program to | |
| 50 | store arguments in system calls and execute them | |
| 51 | out of line in the data segment. | |
| 52 | This preserves the purity of the text segment. | |
| 53 | .PP | |
| 54 | If | |
| 55 | .I indir | |
| 56 | is executed indirectly, | |
| 57 | it is a no-op. | |
| 58 | If the instruction at the indirect | |
| 59 | location is not a system call, | |
| 60 | .I indir | |
| 61 | returns error code EINVAL; | |
| 62 | see | |
| 63 | .IR intro (2). |