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/*
* Linux DTrace
* Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
* Licensed under the Universal Permissive License v 1.0 as shown at
* http://oss.oracle.com/licenses/upl.
*/
#!/usr/sbin/dtrace -s
#pragma D option quiet
#pragma D option strsize=64
/*
* SYNOPSIS
* sudo ./010intro-external-variables.d
*
* DESCRIPTION
* We can examine external variables -- that is, variables from outside
* the D program, such as kernel variables. They are distinguished by
* a back quote ` and constitute a different name space from that of
* the D variables. When such a variables is named, the kernel and all
* loaded modules are searched for the name. Or, you can specify a
* module before the back quote. The kernel itself is module "vmlinux".
* D scripts cannot modify values of kernel variables.
*
* Such external variables are not part of D and are subject to change.
*/
dtrace:::BEGIN
{
printf("\n==== print some kernel variables ====\n\n");
printf("cad_pid->level: %d\n", ((struct pid *)`cad_pid)->level);
printf("crashing_cpu: %d\n", `crashing_cpu);
printf("linux_banner: %s\n", (string)`linux_banner);
printf("linux_proc_banner: %s\n", (string)`linux_proc_banner);
printf("load averages: %d.%02d, %d.%02d, %d.%02d\n",
`avenrun[0] / 2048, ((`avenrun[0] % 2048) * 100) / 2048,
`avenrun[1] / 2048, ((`avenrun[1] % 2048) * 100) / 2048,
`avenrun[2] / 2048, ((`avenrun[2] % 2048) * 100) / 2048);
printf("max_pvn: %d\n", `max_pfn);
printf("nr_cpu_ids: %d\n", `nr_cpu_ids);
printf("saved_command_line: %s\n", (string)`saved_command_line);
printf("\n==== reprint some of them, explicitly naming vmlinux ====\n\n");
printf("crashing_cpu: %d\n", vmlinux`crashing_cpu);
printf("linux_banner: %s\n", (string)vmlinux`linux_banner);
printf("linux_proc_banner: %s\n", (string)vmlinux`linux_proc_banner);
printf("max_pvn: %d\n", vmlinux`max_pfn);
printf("nr_cpu_ids: %d\n", vmlinux`nr_cpu_ids);
printf("\n==== refer to a data type in a module ====\n\n");
printf("offset of atomic in struct rds_message: %d\n",
offsetof(struct rds`rds_message, atomic));
exit(0);
}
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