Fix handling of .note.ABI-tag section for GNU systems [1].

Handle GNU/Linux according to LSB Core Specification 4.0,
Chapter 11. Object Format, 11.8. ABI note tag.

Also check the first word of desc, not only name, according to
glibc abi-tags specification to distinguish between Linux and
kFreeBSD.

Add explicit handling for Debian GNU/kFreeBSD, which runs
on our kernels as well [2].

In {amd64,i386}/trap.c, when checking osrel of the current process,
also check the ABI to not change the signal behaviour for Linux
binary processes, now that we save an osrel version for all three
from the lists above in struct proc [2].

These changes make it possible to run FreeBSD, Debian GNU/kFreeBSD
and Linux binaries on the same machine again for at least i386 and
amd64, and no longer break kFreeBSD which was detected as GNU(/Linux).

PR:		kern/135468
Submitted by:	dchagin [1] (initial patch)
Suggested by:	kib [2]
Tested by:	Petr Salinger (Petr.Salinger seznam.cz) for kFreeBSD
Reviewed by:	kib
MFC after:	3 days

1 files changed, 54 insertions, 6 deletions

diff --git a/sys/kern/imgact_elf.c b/sys/kern/imgact_elf.c
index e2c0a12..6803523 100644
--- a/sys/kern/imgact_elf.c
+++ b/sys/kern/imgact_elf.c
@@ -86,6 +86,9 @@ static int __elfN(load_section)(struct vmspace *vmspace, vm_object_t object,
     vm_offset_t offset, caddr_t vmaddr, size_t memsz, size_t filsz,
     vm_prot_t prot, size_t pagesize);
 static int __CONCAT(exec_, __elfN(imgact))(struct image_params *imgp);
+static boolean_t __elfN(freebsd_trans_osrel)(const Elf_Note *note,
+    int32_t *osrel);
+static boolean_t kfreebsd_trans_osrel(const Elf_Note *note, int32_t *osrel);
 static boolean_t __elfN(check_note)(struct image_params *imgp,
     Elf_Brandnote *checknote, int32_t *osrel);
 
@@ -116,9 +119,56 @@ Elf_Brandnote __elfN(freebsd_brandnote) = {
 	.hdr.n_descsz	= sizeof(int32_t),
 	.hdr.n_type	= 1,
 	.vendor		= FREEBSD_ABI_VENDOR,
-	.flags		= BN_CAN_FETCH_OSREL
+	.flags		= BN_TRANSLATE_OSREL,
+	.trans_osrel	= __elfN(freebsd_trans_osrel)
 };
 
+static boolean_t
+__elfN(freebsd_trans_osrel)(const Elf_Note *note, int32_t *osrel)
+{
+	uintptr_t p;
+
+	p = (uintptr_t)(note + 1);
+	p += roundup2(note->n_namesz, sizeof(Elf32_Addr));
+	*osrel = *(const int32_t *)(p);
+
+	return (TRUE);
+}
+
+static const char GNU_ABI_VENDOR[] = "GNU";
+static int GNU_KFREEBSD_ABI_DESC = 3;
+
+Elf_Brandnote __elfN(kfreebsd_brandnote) = {
+	.hdr.n_namesz	= sizeof(GNU_ABI_VENDOR),
+	.hdr.n_descsz	= 16,	/* XXX at least 16 */
+	.hdr.n_type	= 1,
+	.vendor		= GNU_ABI_VENDOR,
+	.flags		= BN_TRANSLATE_OSREL,
+	.trans_osrel	= kfreebsd_trans_osrel
+};
+
+static boolean_t
+kfreebsd_trans_osrel(const Elf_Note *note, int32_t *osrel)
+{
+	const Elf32_Word *desc;
+	uintptr_t p;
+
+	p = (uintptr_t)(note + 1);
+	p += roundup2(note->n_namesz, sizeof(Elf32_Addr));
+
+	desc = (const Elf32_Word *)p;
+	if (desc[0] != GNU_KFREEBSD_ABI_DESC)
+		return (FALSE);
+
+	/*
+	 * Debian GNU/kFreeBSD embed the earliest compatible kernel version
+	 * (__FreeBSD_version: <major><two digit minor>Rxx) in the LSB way.
+	 */
+	*osrel = desc[1] * 100000 + desc[2] * 1000 + desc[3];
+
+	return (TRUE);
+}
+
 int
 __elfN(insert_brand_entry)(Elf_Brandinfo *entry)
 {
@@ -1371,11 +1421,9 @@ __elfN(check_note)(struct image_params *imgp, Elf_Brandnote *checknote,
 		 * Fetch the osreldate for binary
 		 * from the ELF OSABI-note if necessary.
 		 */
-		if ((checknote->flags & BN_CAN_FETCH_OSREL) != 0 &&
-		    osrel != NULL)
-			*osrel = *(const int32_t *) (note_name +
-			    roundup2(checknote->hdr.n_namesz,
-			    sizeof(Elf32_Addr)));
+		if ((checknote->flags & BN_TRANSLATE_OSREL) != 0 &&
+		    checknote->trans_osrel != NULL)
+			return (checknote->trans_osrel(note, osrel));
 		return (TRUE);
 
 nextnote: