[PATCH v3] powerpc/xmon: Fix tmpstr length check in scanhex

[Madhavan Srinivasan]

If a function name is greater than 63 char long, xmon command
may not find them. For example, here is a test that
executed an illegal instruction in a kernel function and one of
call stack function has name >63 char long,

cpu 0x0: Vector: 700 (Program Check) at [c00000000a6577e0]
    pc: c0000000001aacb8: check__allowed__function__name__for__symbol__r4+0x8/0x10
    lr: c00000000019c1e0: check__allowed__function__name__for__symbol__r1+0x20/0x40
    sp: c00000000a657a80
   msr: 800000000288b033
  current = 0xc00000000a439900
  paca    = 0xc000000003e90000	 irqmask: 0x03	 irq_happened: 0x01
.....
[link register   ] c00000000019c1e0 check__allowed__function__name__for__symbol__r1+0x20/0x40
[c00000000a657a80] c00000000a439900 (unreliable)
[c00000000a657aa0] c0000000001021d8 check__allowed__function__name__for__symbol__r2_resolution_symbol+0x38/0x4c
[c00000000a657ac0] c00000000019b424 power_pmu_event_init+0xa4/0xa50

and when executing a dump instruction (di) command for long function name,
xmon fails to find the function symbol

0:mon> di $check__allowed__function__name__for__symbol__r2_resolution_symbol
unknown symbol 'check__allowed__function__name__for__symbol__r2_resolution_symb'
0000000000000000  ********

This is because, in the scanhex(), tmpstr loop index is checked only for a upper bound
of 63. Proposed fix is to replace the upper bound value with "(KSYM_NAME_LEN-1)"

With fix:

0:mon> di $check__allowed__function__name__for__symbol__r2_resolution_symbol
c0000000001021a0  3c4c0249	addis   r2,r12,585
c0000000001021a4  3842ae60	addi    r2,r2,-20896
c0000000001021a8  7c0802a6	mflr    r0
c0000000001021ac  60000000	nop
.....

Reported-by: Miguel Ojeda <miguel.ojeda.sandonis at gmail.com>
Closes: https://lore.kernel.org/linuxppc-dev/CANiq72=QeTgtZL4k9=4CJP6C_Hv=rh3fsn3B9S3KFoPXkyWk3w@mail.gmail.com/
Signed-off-by: Madhavan Srinivasan <maddy at linux.ibm.com>
---
Changelog v2:
- Fixed the loop upper limit from KSYM_NAME_LEN to
  (KSYM_NAME_LEN - 1) since last index is initialized
  with zero at the end of the loop. Thanks mpe for
  pointing it out. 
- Checkpatch script was complaining about the format style 

	ERROR: spaces required around that '=' (ctx:VxV)
	#67: FILE: arch/powerpc/xmon/xmon.c:3546:
	+		for (i=0; i < (KSYM_NAME_LEN - 1); i++) {
			      ^
   so have fixed the same. 

Changelog v1:
- Updated commit message based on Miguel's review comments

 arch/powerpc/xmon/xmon.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index bd4813bad317..e6cddbb2305f 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -3543,7 +3543,7 @@ scanhex(unsigned long *vp)
 		}
 	} else if (c == '$') {
 		int i;
-		for (i=0; i<63; i++) {
+		for (i = 0; i < (KSYM_NAME_LEN - 1); i++) {
 			c = inchar();
 			if (isspace(c) || c == '\0') {
 				termch = c;
-- 
2.45.2