MySQL Bugs: #58057: 5.1 libmysql/libmysql.c unused variable/compile failure

Bug #58057	5.1 libmysql/libmysql.c unused variable/compile failure
Submitted:	8 Nov 2010 16:18	Modified:	11 Dec 2010 17:36
Reporter:	Paul DuBois	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server: Compiling	Severity:	S3 (Non-critical)
Version:	5.1-security (5.1.54)	OS:	Any
Assigned to:	Davi Arnaut	CPU Architecture:	Any

Description:
libmysql/libmysql.c has an unused variable. This causes compilation failure. Example:

make[2]: Entering directory `/src/extern/MySQL/bzr-mysql/mysql-5.1-security/libmysql'
/bin/sh ../libtool --preserve-dup-deps  --tag=CC   --mode=compile gcc -DDEFAULT_CHARSET_HOME="\"/var/mysql/50154\"" -DMYSQL_DATADIR="\"/var/mysql/50154/data\"" -DDEFAULT_HOME_ENV=MYSQL_HOME -DDEFAULT_GROUP_SUFFIX_ENV=MYSQL_GROUP_SUFFIX -DDEFAULT_SYSCONFDIR="\"/var/mysql/50154/etc\"" -DSHAREDIR="\"/var/mysql/50154/share/mysql\"" -DMYSQL_CLIENT_NO_THREADS -DDONT_USE_RAID  -I. -I../include -I../include -I../include     -Wall -Wextra -Wunused -Wwrite-strings -Wno-strict-aliasing -Werror -g -DSAFE_MUTEX -DSAFEMALLOC -O1   -DUNIV_LINUX -DUNIV_LINUX -MT libmysql.lo -MD -MP -MF .deps/libmysql.Tpo -c -o libmysql.lo libmysql.c
libtool: compile:  gcc -DDEFAULT_CHARSET_HOME=\"/var/mysql/50154\" -DMYSQL_DATADIR=\"/var/mysql/50154/data\" -DDEFAULT_HOME_ENV=MYSQL_HOME -DDEFAULT_GROUP_SUFFIX_ENV=MYSQL_GROUP_SUFFIX -DDEFAULT_SYSCONFDIR=\"/var/mysql/50154/etc\" -DSHAREDIR=\"/var/mysql/50154/share/mysql\" -DMYSQL_CLIENT_NO_THREADS -DDONT_USE_RAID -I. -I../include -I../include -I../include -Wall -Wextra -Wunused -Wwrite-strings -Wno-strict-aliasing -Werror -g -DSAFE_MUTEX -DSAFEMALLOC -O1 -DUNIV_LINUX -DUNIV_LINUX -MT libmysql.lo -MD -MP -MF .deps/libmysql.Tpo -c libmysql.c  -fPIC -DPIC -o .libs/libmysql.o
cc1: warnings being treated as errors
libmysql.c: In function ‘mysql_server_init’:
libmysql.c:134: error: unused variable ‘serv_ptr’
make[2]: *** [libmysql.lo] Error 1
make[2]: Leaving directory `/src/extern/MySQL/bzr-mysql/mysql-5.1-security/libmysql'
make[1]: *** [all] Error 2
make[1]: Leaving directory `/src/extern/MySQL/bzr-mysql/mysql-5.1-security/libmysql'
make: *** [all-recursive] Error 1

Removing line 134 enables compilation to succeed. I don't think that's quite the correct fix, because it actually is used later on in the source, if the right combination of symbols is defined.

Note: I sometimes have successful compilation with "make clean; make". But if I immediately type "make" again, compilation fails as shown above.

How to repeat:
Here is my configuration:

VERSION=50154

PREFIX="/var/mysql/$VERSION"
PORT=$VERSION
HANDLERS="
  --with-plugins=archive,blackhole,csv,example,federated,innobase,partition
"
DOCS="--without-docs --without-man"
OTHER="
  --enable-local-infile
  --enable-thread-safe-client
  --with-comment=
  --with-debug=full
  --with-embedded-server
  --with-extra-charsets=all
  --without-readline
  --with-ssl
"
rm -f config.cache
CFLAGS=-O1 \
./configure \
  --prefix=$PREFIX \
  --localstatedir=$PREFIX/data \
  --with-unix-socket-path=$PREFIX/mysql.sock \
  --with-tcp-port=$PORT \
  $HANDLERS $DOCS $OTHER

Suggested fix:
Probably the variable declaration needs protection with the same ifdefs as the variable's use later on.

Thank you for the report.

Do you use BZR repository? I can not repeat described behavior with today update and get error

cc1plus: warnings being treated as errors
debug_sync.cc: In function ‘void debug_sync_execute(THD*, st_debug_sync_action*)’:
debug_sync.cc:1721: error: ‘old_proc_info’ may be used uninitialized in this function
make[3]: *** [debug_sync.o] Error 1

instead.

A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/123501

3503 Davi Arnaut	2010-11-10
      Bug#58057: 5.1 libmysql/libmysql.c unused variable/compile failure
      Bug#57995: Compiler flag change build error on OSX 10.4: my_getncpus.c
      Bug#57996: Compiler flag change build error on OSX 10.5 : bind.c
      Bug#57994: Compiler flag change build error : my_redel.c
      Bug#57993: Compiler flag change build error on FreeBsd 7.0 : regexec.c
      Bug#57992: Compiler flag change build error on FreeBsd : mf_keycache.c
      Bug#57997: Compiler flag change build error on OSX 10.6: debug_sync.cc
      
      Fix assorted compiler generated warnings.
     @ cmd-line-utils/readline/bind.c
        Bug#57996: Compiler flag change build error on OSX 10.5 : bind.c
        
        Initialize variable to work around a false positive warning.
     @ include/m_string.h
        Bug#57994: Compiler flag change build error : my_redel.c
        
        The expansion of stpcpy (in glibc) causes warnings if the
        return value of strmov is not being used. Since stpcpy is
        a GNU extension and the expansion ends up using a built-in
        provided by GCC, use the compiler provided built-in directly
        when possible.
     @ include/my_compiler.h
        Define a dummy MY_GNUC_PREREQ when not compiling with GCC.
     @ libmysql/libmysql.c
        Bug#58057: 5.1 libmysql/libmysql.c unused variable/compile failure
        
        Variable might not be used in some cases. So, tag it as unused.
     @ mysys/mf_keycache.c
        Bug#57992: Compiler flag change build error on FreeBsd : mf_keycache.c
        
        Use UNINIT_VAR to work around a false positive warning.
     @ mysys/my_getncpus.c
        Bug#57995: Compiler flag change build error on OSX 10.4: my_getncpus.c
        
        Declare variable in the same block where it is used.
     @ regex/regexec.c
        Bug#57993: Compiler flag change build error on FreeBsd 7.0 : regexec.c
        
        Work around a compiler bug which causes the cast to not be enforced.
     @ sql/debug_sync.cc
        Bug#57997: Compiler flag change build error on OSX 10.6: debug_sync.cc
        
        Use UNINIT_VAR to work around a false positive warning.
     @ sql/handler.cc
        Use UNINIT_VAR to work around a false positive warning.
     @ sql/slave.cc
        Use UNINIT_VAR to work around a false positive warning.
     @ sql/sql_partition.cc
        Use UNINIT_VAR to work around a false positive warning.
     @ storage/myisam/ft_nlq_search.c
        Use UNINIT_VAR to work around a false positive warning.
     @ storage/myisam/mi_create.c
        Use UNINIT_VAR to work around a false positive warning.
     @ storage/myisammrg/myrg_open.c
        Use UNINIT_VAR to work around a false positive warning.
     @ tests/mysql_client_test.c
        Change function to take a pointer to const, no need for a cast.

Ok to push.

Pushed into mysql-5.1-bugteam and up.

Noted in 5.1.54, 5.5.8 changelogs.

Several compilation problems were fixed.

Pushed into mysql-trunk 5.6.1 (revid:alexander.nozdrin@oracle.com-20101205122447-6x94l4fmslpbttxj) (version source revid:alexander.nozdrin@oracle.com-20101205122447-6x94l4fmslpbttxj) (merge vers: 5.6.1) (pib:23)

Pushed into mysql-5.1 5.1.55 (revid:sunanda.menon@oracle.com-20101215054055-vgwki317xg1wphhh) (version source revid:sunanda.menon@oracle.com-20101215054055-vgwki317xg1wphhh) (merge vers: 5.1.55) (pib:23)

Pushed into mysql-5.5 5.5.9 (revid:jonathan.perkin@oracle.com-20101216101358-fyzr1epq95a3yett) (version source revid:jonathan.perkin@oracle.com-20101216101358-fyzr1epq95a3yett) (merge vers: 5.5.9) (pib:24)