Fix an issue with gdb triggering assertions in kgdb on i386.

The kgdb targets use runtime assertions on native targets to verify
that the helper arrays documenting the layout of things like the PCB
and trapframe structures match.  Ideally these asserts would be
compile time assertions, but they cannot be checked at compile time.
Instead, they are checked at runtime during gdb startup.

However, the layout of the i386 PCB changed when the AVX changes were
merged to i386.  The constants in the i386 target assume the post-AVX
layout, but gdb packages on stable branches might be built against
pre-AVX worlds.  In that case, those gdb binaries will trigger these
assertions on every invocation.

As a workaround, disable the PCB-related assertions on pre-AVX worlds.
If kgdb is run against a pre-AVX kernel it will not be able to parse
the PCB correctly, but userland debugging should work fine.  kgdb
built against a pre-AVX world but run against an AVX kernel should
work fine.

PR:		209061
Reported by:	trasz
Approved by:	luca.pizzamiglio@gmail.com (maintainer), swills

2 files changed, 16 insertions, 1 deletions

diff --git a/devel/gdb/Makefile b/devel/gdb/Makefile
index 36b90c542250..2243970a6c45 100644
--- a/devel/gdb/Makefile
+++ b/devel/gdb/Makefile
@@ -3,7 +3,7 @@
 
 PORTNAME=	gdb
 PORTVERSION=	7.11
-#PORTREVISION=
+PORTREVISION=	1
 CATEGORIES=	devel
 MASTER_SITES=	GNU
 
diff --git a/devel/gdb/files/kgdb/i386fbsd-kern.c b/devel/gdb/files/kgdb/i386fbsd-kern.c
index 37e658fcf7f8..6937efea237c 100644
--- a/devel/gdb/files/kgdb/i386fbsd-kern.c
+++ b/devel/gdb/files/kgdb/i386fbsd-kern.c
@@ -478,6 +478,20 @@ _initialize_i386_kgdb_tdep(void)
 	    i386fbsd_pspace_data_cleanup);
 
 #ifdef __i386__
+	/*
+	 * FreeBSD/i386 kernels prior to the introduction of AVX
+	 * support used a different layout for the PCB.  If gdb is
+	 * compiled on these systems, these asserts will fail.  The
+	 * package builders build packages on older systems which are
+	 * then run on newer systems.  These binaries trip over these
+	 * assertions even when debugging user programs and even
+	 * though the running kernel is new enough.  To cope, disable
+	 * the assertion checks unless gdb is built against a new
+	 * enough world.  Note that this means kgdb is not going to
+	 * parse PCBs correctly on FreeBSD/i386 kernels before AVX was
+	 * merged.
+	 */
+#if __FreeBSD_version >= 1001505
 	gdb_assert(offsetof(struct pcb, pcb_ebx)
 		   == i386fbsd_pcb_offset[I386_EBX_REGNUM]);
 	gdb_assert(offsetof(struct pcb, pcb_esp)
@@ -490,6 +504,7 @@ _initialize_i386_kgdb_tdep(void)
 		   == i386fbsd_pcb_offset[I386_EDI_REGNUM]);
 	gdb_assert(offsetof(struct pcb, pcb_eip)
 		   == i386fbsd_pcb_offset[I386_EIP_REGNUM]);
+#endif
 	gdb_assert(CODE_SEL == GSEL(GCODE_SEL, SEL_KPL));
 	gdb_assert(DATA_SEL == GSEL(GDATA_SEL, SEL_KPL));
 	gdb_assert(PRIV_SEL == GSEL(GPRIV_SEL, SEL_KPL));