Include process IDs in core dumps.

When threads were added to the kernel, the pr_pid member of the
NT_PRSTATUS note was repurposed to store LWP IDs instead of process
IDs.  However, the process ID was no longer recorded in core dumps.
This change adds a pr_pid field to prpsinfo (NT_PRSINFO).  Rather than
bumping the prpsinfo version number, note parsers can use the note's
payload size to determine if pr_pid is present.

Reviewed by:	kib, emaste (older version)
MFC after:	2 months
Differential Revision:	https://reviews.freebsd.org/D7117

sys/kern/imgact_elf.c

@@ -1874,6 +1874,7 @@ __elfN(note_prpsinfo)(void *arg, struct sbuf *sb, size_t *sizep)
 				*cp = ' ';
 			}
 		}
+		psinfo->pr_pid = p->p_pid;
 		sbuf_bcat(sb, psinfo, sizeof(*psinfo));
 		free(psinfo, M_TEMP);
 	}

sys/sys/procfs.h

@@ -49,7 +49,10 @@ typedef struct fpreg fpregset_t;
 
 /*
  * The parenthsized numbers like (1) indicate the minimum version number
- * for which each element exists in the structure.
+ * for which each element exists in the structure.  The version number is
+ * not bumped when adding new fields to the end, only if the meaning of
+ * an existing field changes.  Additional fields are annotated as (1a),
+ * (1b), etc. to indicate the groupings of additions.
  */
 
 #define PRSTATUS_VERSION	1	/* Current version of prstatus_t */
@@ -61,7 +64,7 @@ typedef struct prstatus {
     size_t	pr_fpregsetsz;	/* sizeof(fpregset_t) (1) */
     int		pr_osreldate;	/* Kernel version (1) */
     int		pr_cursig;	/* Current signal (1) */
-    pid_t	pr_pid;		/* Process ID (1) */
+    pid_t	pr_pid;		/* LWP (Thread) ID (1) */
     gregset_t	pr_reg;		/* General purpose registers (1) */
 } prstatus_t;
 
@@ -78,6 +81,7 @@ typedef struct prpsinfo {
     size_t	pr_psinfosz;	/* sizeof(prpsinfo_t) (1) */
     char	pr_fname[PRFNAMESZ+1];	/* Command name, null terminated (1) */
     char	pr_psargs[PRARGSZ+1];	/* Arguments, null terminated (1) */
+    pid_t	pr_pid;		/* Process ID (1a) */
 } prpsinfo_t;
 
 typedef struct thrmisc {
@@ -104,6 +108,7 @@ typedef struct prpsinfo32 {
 	uint32_t pr_psinfosz;
 	char	pr_fname[PRFNAMESZ+1];
 	char	pr_psargs[PRARGSZ+1];
+	int32_t	pr_pid;
 } prpsinfo32_t;
 
 struct thrmisc32 {

usr.bin/gcore/elfcore.c

@@ -586,6 +586,7 @@ elf_note_prpsinfo(void *arg, size_t *sizep)
 	} else
 		strlcpy(psinfo->pr_psargs, kip.ki_comm,
 		    sizeof(psinfo->pr_psargs));
+	psinfo->pr_pid = pid;
 
 	*sizep = sizeof(*psinfo);
 	return (psinfo);