commit e08b05fb4af43520d97dc761f328acaaf45bcb79
Author: Brandon Bergren <git@bdragon.rtk0.net>
Date:   Thu Feb 6 13:29:54 2020 -0600

    Low level mchk dumper

diff --git a/sys/powerpc/aim/aim_machdep.c b/sys/powerpc/aim/aim_machdep.c
index c18bf6ce0a7..c346251e21a 100644
--- a/sys/powerpc/aim/aim_machdep.c
+++ b/sys/powerpc/aim/aim_machdep.c
@@ -157,6 +157,7 @@ extern void	*dsitrap_bridgemode, *dsiend_bridgemode;
 #endif
 extern void	*decrint, *decrsize;
 extern void     *extint, *extsize;
+extern void	*mchk_dblow;
 extern void	*dblow, *dbend;
 extern void	*imisstrap, *imisssize;
 extern void	*dlmisstrap, *dlmisssize;
@@ -403,8 +404,8 @@ aim_cpu_init(vm_offset_t toc)
 	    (size_t)&rstcode);
 
 #ifdef KDB
-	bcopy(&dblow, (void *)(EXC_MCHK + trap_offset), (size_t)&dbend -
-	    (size_t)&dblow);
+	bcopy(&mchk_dblow, (void *)(EXC_MCHK + trap_offset), (size_t)&dbend -
+	    (size_t)&mchk_dblow);
 	bcopy(&dblow, (void *)(EXC_PGM + trap_offset), (size_t)&dbend -
 	    (size_t)&dblow);
 	bcopy(&dblow, (void *)(EXC_TRC + trap_offset), (size_t)&dbend -
diff --git a/sys/powerpc/aim/trap_subr64.S b/sys/powerpc/aim/trap_subr64.S
index 69a146ece70..71a50bd4ace 100644
--- a/sys/powerpc/aim/trap_subr64.S
+++ b/sys/powerpc/aim/trap_subr64.S
@@ -936,6 +936,48 @@ dbleave:
 	FRAME_LEAVE(PC_DBSAVE)
 	rfid
 
+
+	.globl	CNAME(mchk_dblow)
+	.p2align 3
+CNAME(mchk_dblow):
+/*
+ * When we get a MCE, we need to dump some additional info while we have
+ * a chance.
+ */
+	mtsprg1 %r1			/* save SP */
+	mtsprg2	%r28			/* save r28 */
+	mfcr	%r28			/* save CR in r28 */
+
+	/*
+	 * For MCE debug, we don't care what mode we're in yet.
+	 * We will dump out the SLB either way.
+	 */
+        GET_CPUINFO(%r1)
+        std     %r29,(PC_DBSAVE+CPUSAVE_R29)(%r1)       /* free r29 */
+        std     %r30,(PC_DBSAVE+CPUSAVE_R30)(%r1)       /* free r30 */
+        std     %r31,(PC_DBSAVE+CPUSAVE_R31)(%r1)       /* free r31 */
+
+	li	%r29, 0		/* set counter to zero */
+	mr	%r30, %r1
+	addi	%r30, %r30, SLB_DEBUG /* set r30 to slb_debug[0] */
+1:
+	/* Read the SLB into the slb_debug array. */
+	slbmfee	%r31, %r29
+	std	%r31, 0(%r30)
+	slbmfev %r31, %r29
+	std	%r31, 8(%r30)
+	addi	%r30, %r30, 16
+	cmpdi	%r29, 32 /* 64 on PPC970? */
+	beq-	1b
+
+	/* Put things back like they were and fall through to dblow. */
+	ld	%r31, (PC_DBSAVE+CPUSAVE_R31)(%r1)
+	ld	%r30, (PC_DBSAVE+CPUSAVE_R30)(%r1)
+	ld	%r29, (PC_DBSAVE+CPUSAVE_R29)(%r1)
+	mtcr	%r28
+	mfsprg2	%r28
+	mfsprg1	%r1
+
 /*
  * In case of KDB we want a separate trap catcher for it
  */
diff --git a/sys/powerpc/include/pcpu.h b/sys/powerpc/include/pcpu.h
index 76829ea50df..e3ea9a1ad40 100644
--- a/sys/powerpc/include/pcpu.h
+++ b/sys/powerpc/include/pcpu.h
@@ -65,11 +65,12 @@ struct pvo_entry;
 	struct slb	slb[64];					\
 	struct slb	**userslb;					\
 	register_t	slbsave[18];					\
-	uint8_t		slbstack[1024];				\
+	uint8_t		slbstack[1024];					\
 	struct pvo_entry *qmap_pvo;					\
 	struct mtx	qmap_lock;					\
 	uint64_t	opal_hmi_flags;					\
-	char		__pad[1337];
+	struct slb	slbdebug[64];					\
+	char		__pad[313];
 
 #ifdef __powerpc64__
 #define PCPU_MD_AIM_FIELDS	PCPU_MD_AIM64_FIELDS
diff --git a/sys/powerpc/powerpc/genassym.c b/sys/powerpc/powerpc/genassym.c
index 8c632a4027b..a4c1f991efb 100644
--- a/sys/powerpc/powerpc/genassym.c
+++ b/sys/powerpc/powerpc/genassym.c
@@ -116,6 +116,7 @@ ASSYM(PC_SLBSTACK, offsetof(struct pcpu, pc_aim.slbstack));
 ASSYM(USER_SLB_SLOT, USER_SLB_SLOT);
 ASSYM(USER_SLB_SLBE, USER_SLB_SLBE);
 ASSYM(SEGMENT_MASK, SEGMENT_MASK);
+ASSYM(SLB_DEBUG, offsetof(struct pcpu, pc_aim.slbdebug));
 #else
 ASSYM(PM_SR, offsetof(struct pmap, pm_sr));
 ASSYM(USER_SR, USER_SR);