Implement fetching of the __FreeBSD_version from the ELF ABI-tag note.

The value is read into the p_osrel member of the struct proc. p_osrel
is set to 0 for the binaries without the note.

MFC after:	3 days

sys/kern/imgact_elf.c

@@ -597,11 +597,13 @@ __elfN(load_file)(struct proc *p, const char *file, u_long *addr,
 	return (error);
 }
 
+static const char FREEBSD_ABI_VENDOR[] = "FreeBSD";
+
 static int
 __CONCAT(exec_, __elfN(imgact))(struct image_params *imgp)
 {
 	const Elf_Ehdr *hdr = (const Elf_Ehdr *)imgp->image_header;
-	const Elf_Phdr *phdr;
+	const Elf_Phdr *phdr, *pnote = NULL;
 	Elf_Auxargs *elf_auxargs;
 	struct vmspace *vmspace;
 	vm_prot_t prot;
@@ -612,7 +614,9 @@ __CONCAT(exec_, __elfN(imgact))(struct image_params *imgp)
 	int error = 0, i;
 	const char *interp = NULL;
 	Elf_Brandinfo *brand_info;
+	const Elf_Note *note, *note_end;
 	char *path;
+	const char *note_name;
 	struct thread *td = curthread;
 	struct sysentvec *sv;
 
@@ -754,6 +758,9 @@ __CONCAT(exec_, __elfN(imgact))(struct image_params *imgp)
 		case PT_PHDR: 	/* Program header table info */
 			proghdr = phdr[i].p_vaddr;
 			break;
+		case PT_NOTE:
+			pnote = &phdr[i];
+			break;
 		default:
 			break;
 		}
@@ -835,6 +842,41 @@ __CONCAT(exec_, __elfN(imgact))(struct image_params *imgp)
 	imgp->auxargs = elf_auxargs;
 	imgp->interpreted = 0;
 
+	/*
+	 * Try to fetch the osreldate for FreeBSD binary from the ELF
+	 * OSABI-note. Only the first page of the image is searched,
+	 * the same as for headers.
+	 */
+	if (pnote != NULL && pnote->p_offset < PAGE_SIZE &&
+	    pnote->p_offset + pnote->p_filesz < PAGE_SIZE ) {
+		note = (const Elf_Note *)(imgp->image_header + pnote->p_offset);
+		if (!aligned(note, Elf32_Addr)) {
+			free(imgp->auxargs, M_TEMP);
+			imgp->auxargs = NULL;
+			return (ENOEXEC);
+		}
+		note_end = (const Elf_Note *)(imgp->image_header + pnote->p_offset +
+		    pnote->p_filesz);
+		while (note < note_end) {
+			if (note->n_namesz == sizeof(FREEBSD_ABI_VENDOR) &&
+			    note->n_descsz == sizeof(int32_t) &&
+			    note->n_type == 1 /* ABI_NOTETYPE */) {
+				note_name = (const char *)(note + 1);
+				if (strncmp(FREEBSD_ABI_VENDOR, note_name,
+				    sizeof(FREEBSD_ABI_VENDOR)) == 0) {
+					imgp->proc->p_osrel = *(const int32_t *)
+					    (note_name +
+					    round_page_ps(sizeof(FREEBSD_ABI_VENDOR),
+						sizeof(Elf32_Addr)));
+					break;
+				}
+			}
+			note = (const Elf_Note *)((const char *)(note + 1) +
+			    round_page_ps(note->n_namesz, sizeof(Elf32_Addr)) +
+			    round_page_ps(note->n_descsz, sizeof(Elf32_Addr)));
+		}
+	}
+
 	return (error);
 }
 
@@ -901,8 +943,6 @@ static void __elfN(puthdr)(struct thread *, void *, size_t *, int);
 static void __elfN(putnote)(void *, size_t *, const char *, int,
     const void *, size_t);
 
-extern int osreldate;
-
 int
 __elfN(coredump)(td, vp, limit)
 	struct thread *td;

sys/kern/init_main.c

@@ -373,9 +373,10 @@ proc0_init(void *dummy __unused)
 	td = &thread0;
 	
 	/*
-	 * Initialize magic number.
+	 * Initialize magic number and osrel.
 	 */
 	p->p_magic = P_MAGIC;
+	p->p_osrel = osreldate;
 
 	/*
 	 * Initialize thread and process structures.

sys/kern/kern_exec.c

@@ -391,6 +391,7 @@ do_execve(td, args, mac_p)
 	if (error)
 		goto exec_fail_dealloc;
 
+	imgp->proc->p_osrel = 0;
 	/*
 	 *	If the current process has a special image activator it
 	 *	wants to try first, call it.   For example, emulating shell

sys/kern/kern_mib.c

@@ -104,7 +104,6 @@ SYSCTL_STRING(_kern, KERN_OSTYPE, ostype, CTLFLAG_RD,
  * NOTICE: The *userland* release date is available in
  * /usr/include/osreldate.h
  */
-extern int osreldate;
 SYSCTL_INT(_kern, KERN_OSRELDATE, osreldate, CTLFLAG_RD,
     &osreldate, 0, "Kernel release date");
 

sys/sys/proc.h

@@ -561,6 +561,8 @@ struct proc {
 /* The following fields are all copied upon creation in fork. */
 #define	p_startcopy	p_endzero
 	u_int		p_magic;	/* (b) Magic number. */
+	int		p_osrel;	/* (x) osreldate for the
+					       binary (from ELF note, if any) */
 	char		p_comm[MAXCOMLEN + 1];	/* (b) Process name. */
 	struct pgrp	*p_pgrp;	/* (c + e) Pointer to process group. */
 	struct sysentvec *p_sysent;	/* (b) Syscall dispatch info. */

sys/sys/systm.h

@@ -101,6 +101,7 @@ extern int maxusers;		/* system tune hint */
  * in two files.
  * XXX most of these variables should be const.
  */
+extern int osreldate;
 extern int envmode;
 extern int hintmode;		/* 0 = off. 1 = config, 2 = fallback */
 extern int dynamic_kenv;