linux-kernel - [RFC] powerpc: xmon: Add address lookup for percpu symbols

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Date:   Thu, 17 Nov 2016 17:40:35 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Cc:     Boqun Feng <boqun.feng@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Andrew Donnellan <andrew.donnellan@....ibm.com>,
        Christophe Leroy <christophe.leroy@....fr>,
        "Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
        Rashmica Gupta <rashmicy@...il.com>,
        Douglas Miller <dougmill@...ux.vnet.ibm.com>
Subject: [RFC] powerpc: xmon: Add address lookup for percpu symbols

Currently, in xmon, there is no obvious way to get an address for a
percpu symbol for a particular cpu. Having such an ability would be good
for debugging the system when percpu variables got involved.

Therefore, this patch introduces a new xmon command "lp" to lookup the
address for percpu symbols. Usage of "lp" is similar to "ls", except
that we could add a cpu number to choose the variable of which cpu we
want to lookup. If no cpu number is given, lookup for current cpu.

Signed-off-by: Boqun Feng <boqun.feng@...il.com>
---
 arch/powerpc/xmon/xmon.c | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index 760545519a0b..3556966a29a5 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -229,6 +229,7 @@ Commands:\n\
   f	flush cache\n\
   la	lookup symbol+offset of specified address\n\
   ls	lookup address of specified symbol\n\
+  lp s [#]	lookup address of percpu symbol s for current cpu, or cpu #\n\
   m	examine/change memory\n\
   mm	move a block of memory\n\
   ms	set a block of memory\n\
@@ -2943,7 +2944,7 @@ static void
 symbol_lookup(void)
 {
 	int type = inchar();
-	unsigned long addr;
+	unsigned long addr, cpu, offset;
 	static char tmp[64];
 
 	switch (type) {
@@ -2967,6 +2968,31 @@ symbol_lookup(void)
 		catch_memory_errors = 0;
 		termch = 0;
 		break;
+	case 'p':
+		getstring(tmp, 64);
+		if (setjmp(bus_error_jmp) == 0) {
+			catch_memory_errors = 1;
+			sync();
+			addr = kallsyms_lookup_name(tmp);
+			sync();
+		}
+
+		if (scanhex(&cpu) && cpu < num_possible_cpus())
+			offset = per_cpu_offset(cpu);
+		else {
+			offset = my_cpu_offset;
+			cpu = raw_smp_processor_id();
+		}
+
+		if (addr)
+			printf("%s for cpu 0x%lx: %lx\n", tmp, cpu,
+							  addr + offset);
+		else
+			printf("Percpu symbol '%s' not found.\n", tmp);
+
+		catch_memory_errors = 0;
+		termch = 0;
+		break;
 	}
 }
 
-- 
2.10.1