From 926da0492a672c3175d81f24bfa1b4ad461b884b Mon Sep 17 00:00:00 2001
From: Leandro Lupori <luporl@FreeBSD.org>
Date: Thu, 5 Nov 2020 16:47:23 +0000
Subject: [PATCH] pmcstat: fix PPC kernel symbol resolution

PowerPC kernel is of DYN type and it has a base address where it is
initially loaded, before being relocated. As the start address passed to
pmcstat_image_link() is where the kernel was relocated to, but the symbols
always use the original base address, we need to subtract it to get the
correct offset.

Reviewed by:	jhibbits
Sponsored by:	Eldorado Research Institute (eldorado.org.br)
Differential Revision:	https://reviews.freebsd.org/D26114
---
 lib/libpmcstat/libpmcstat_image.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/lib/libpmcstat/libpmcstat_image.c b/lib/libpmcstat/libpmcstat_image.c
index 94d103228d28..9ee7097e95ec 100644
--- a/lib/libpmcstat/libpmcstat_image.c
+++ b/lib/libpmcstat/libpmcstat_image.c
@@ -32,6 +32,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/param.h>
 #include <sys/endian.h>
 #include <sys/pmc.h>
+#include <sys/sysctl.h>
 #include <sys/imgact_aout.h>
 #include <sys/imgact_elf.h>
 
@@ -176,6 +177,10 @@ pmcstat_image_link(struct pmcstat_process *pp, struct pmcstat_image *image,
 {
 	struct pmcstat_pcmap *pcm, *pcmnew;
 	uintfptr_t offset;
+#ifdef __powerpc__
+	unsigned long kernbase;
+	size_t kernbase_len;
+#endif
 
 	assert(image->pi_type != PMCSTAT_IMAGE_UNKNOWN &&
 	    image->pi_type != PMCSTAT_IMAGE_INDETERMINABLE);
@@ -183,6 +188,26 @@ pmcstat_image_link(struct pmcstat_process *pp, struct pmcstat_image *image,
 	if ((pcmnew = malloc(sizeof(*pcmnew))) == NULL)
 		err(EX_OSERR, "ERROR: Cannot create a map entry");
 
+	/*
+	 * PowerPC kernel is of DYN type and it has a base address
+	 * where it is initially loaded, before being relocated.
+	 * As the address in 'start' is where the kernel was relocated to,
+	 * but the symbols always use the original base address, we need to
+	 * subtract it to get the correct offset.
+	 */
+#ifdef __powerpc__
+	if (pp->pp_pid == -1) {
+		kernbase = 0;
+		kernbase_len = sizeof(kernbase);
+		if (sysctlbyname("kern.base_address", &kernbase, &kernbase_len,
+		    NULL, 0) == -1)
+			warnx(
+			    "WARNING: Could not retrieve kernel base address");
+		else
+			start -= kernbase;
+	}
+#endif
+
 	/*
 	 * Adjust the map entry to only cover the text portion
 	 * of the object.