Fix arm stack frame walking support:

- Adjust stack offset for Clang
- Correctly fill registers for fake stack frame (soft PMC)

MFC after:	1 week
Sponsored by:	Stormshield
Differential Revision:	https://reviews.freebsd.org/D7396

1 files changed, 15 insertions, 4 deletions

diff --git a/sys/dev/hwpmc/hwpmc_arm.c b/sys/dev/hwpmc/hwpmc_arm.c
index a2a25a98d2f3..94f29922290b 100644
--- a/sys/dev/hwpmc/hwpmc_arm.c
+++ b/sys/dev/hwpmc/hwpmc_arm.c
@@ -42,6 +42,17 @@ __FBSDID("$FreeBSD$");
 #include <vm/vm_param.h>
 #include <vm/pmap.h>
 
+/* XXX: Userland code compiled with gcc will need an heuristic
+ * to be correctly detected. 
+ */
+#ifdef __clang__
+#define PC_OFF 1
+#define FP_OFF 0
+#else
+#define PC_OFF -1
+#define FP_OFF -3
+#endif
+
 struct pmc_mdep *
 pmc_md_initialize()
 {
@@ -100,7 +111,7 @@ pmc_save_kernel_callchain(uintptr_t *cc, int maxsamples,
 
 	for (count = 1; count < maxsamples; count++) {
 		/* Use saved lr as pc. */
-		r = fp - sizeof(uintptr_t);
+		r = fp + PC_OFF * sizeof(uintptr_t);
 		if (!PMC_IN_KERNEL_STACK(r, stackstart, stackend))
 			break;
 		pc = *(uintptr_t *)r;
@@ -110,7 +121,7 @@ pmc_save_kernel_callchain(uintptr_t *cc, int maxsamples,
 		*cc++ = pc;
 
 		/* Switch to next frame up */
-		r = fp - 3 * sizeof(uintptr_t);
+		r = fp + FP_OFF * sizeof(uintptr_t);
 		if (!PMC_IN_KERNEL_STACK(r, stackstart, stackend))
 			break;
 		fp = *(uintptr_t *)r;
@@ -147,7 +158,7 @@ pmc_save_user_callchain(uintptr_t *cc, int maxsamples,
 
 	for (count = 1; count < maxsamples; count++) {
 		/* Use saved lr as pc. */
-		r = fp - sizeof(uintptr_t);
+		r = fp + PC_OFF * sizeof(uintptr_t);
 		if (copyin((void *)r, &pc, sizeof(pc)) != 0)
 			break;
 		if (!PMC_IN_USERSPACE(pc))
@@ -157,7 +168,7 @@ pmc_save_user_callchain(uintptr_t *cc, int maxsamples,
 
 		/* Switch to next frame up */
 		oldfp = fp;
-		r = fp - 3 * sizeof(uintptr_t);
+		r = fp + FP_OFF * sizeof(uintptr_t);
 		if (copyin((void *)r, &fp, sizeof(fp)) != 0)
 			break;
 		if (fp < oldfp || !PMC_IN_USERSPACE(fp))