The ls (lookup symbol) and zr (reboot) commands use xmon's getstring()
helper to read a string argument from the xmon prompt. This function skips
over leading whitespace, but doesn't check if the first "non-whitespace"
character is a newline which causes some odd behaviour (<enter> indicates
a the enter key was pressed):

        0:mon> ls printk<enter>
        printk: c0000000001680c4

        0:mon> ls<enter>
        printk<enter>
        Symbol '
        printk' not found.
        0:mon>

With commit 2d9b332d99b ("powerpc/xmon: Allow passing an argument
to ppc_md.restart()") we have a similar problem with the zr command.
Previously zr took no arguments so "zr<enter> would trigger a reboot.
With that patch applied a second newline needs to be sent in order for
the reboot to occur. Fix this by checking if the leading whitespace
ended on a newline:

        0:mon> ls<enter>
        Symbol '' not found.

Fixes: 2d9b332d99b ("powerpc/xmon: Allow passing an argument to 
ppc_md.restart()")
Reported-by: Michael Ellerman <m...@ellerman.id.au>
Signed-off-by: Oliver O'Halloran <ooh...@gmail.com>
---
 arch/powerpc/xmon/xmon.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index e8c84d26..0ec9640 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -3435,6 +3435,11 @@ getstring(char *s, int size)
        int c;
 
        c = skipbl();
+       if (c == '\n') {
+               *s = 0;
+               return;
+       }
+
        do {
                if( size > 1 ){
                        *s++ = c;
-- 
2.9.5

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