BUG #8397: pg_basebackup -x from new standby server sometimes causes Segmentation fault

The following bug has been logged on the website:

Bug reference: 8397
Logged by: TAKATSUKA Haruka
Email address: harukat(at)sraoss(dot)co(dot)jp
PostgreSQL version: 9.2.4
Operating system: Linux (CentOS6)
Description:

Hi.

I report a small bug.
pg_basebackup -x from new standby server sometimes causes Segmentation
fault.

(1) create new standby server dir by pg_basebackup without -x
(2) start new standby server
(3) pg_basebackup from new standby server with -x
(!) when new standby has no WAL files in pg_xlog,
new standby's wal sender crash

new standby server's core file:

Core was generated by `postgres: wal sender process postgres ::1(55210)
sending backup "pg_basebackup'.
Program terminated with signal 11, Segmentation fault.
#0 0x0000003b7368ac66 in __rawmemchr_sse2 () from /lib64/libc.so.6
Missing separate debuginfos, use: debuginfo-install
glibc-2.12-1.107.el6.x86_64 libxml2-2.7.6-4.el6.x86_64
zlib-1.2.3-27.el6.x86_64
(gdb) bt
#0 0x0000003b7368ac66 in __rawmemchr_sse2 () from /lib64/libc.so.6
#1 0x0000003b73675990 in _IO_str_init_static_internal () from
/lib64/libc.so.6
#2 0x0000003b73669935 in vsscanf () from /lib64/libc.so.6
#3 0x0000003b736639a8 in sscanf () from /lib64/libc.so.6
#4 0x0000000000622351 in perform_base_backup (opt=0x7fffc2e22300,
tblspcdir=0xd424c0) at basebackup.c:304
#5 0x0000000000622c50 in SendBaseBackup (cmd=<value optimized out>)
at basebackup.c:558
#6 0x000000000061f5b0 in HandleReplicationCommand () at walsender.c:482
#7 WalSndHandshake () at walsender.c:257
#8 WalSenderMain () at walsender.c:181
#9 0x0000000000650b12 in PostgresMain (argc=1, argv=<value optimized out>,
dbname=0xc82a90 "", username=0xc82a70 "postgres") at postgres.c:3715
#10 0x000000000060c4f1 in BackendRun () at postmaster.c:3614
#11 BackendStartup () at postmaster.c:3304
#12 ServerLoop () at postmaster.c:1367
#13 0x000000000060f031 in PostmasterMain (argc=<value optimized out>,
argv=<value optimized out>) at postmaster.c:1127
#14 0x00000000005ae140 in main (argc=5, argv=0xc80bb0) at main.c:199

./backend/replication/basebackup.c:304
XLogFromFileName(walFiles[0], &tli, &logid, &logseg);

In this case, nWalFiles = 0 and walFiles[] palloced zero size.

Though pg_basebackup does not have to work in this rare case,
we should insert something like "if (nWalFiles <= 0) ereport(...);".

regards,