Here is a simplified Makefile showing this bug:
cat >Makefile <<"EOF"
%.bar: %.c foo.h
cat $^ >$@ || rm $@
foo.h: foo.h.in
cat $^ >$@ || rm $@
EOF
cat >main.y <"EOF"
%%
command:
"q" { return 1; }
;
%%
EOF
echo bar >foo.h.in
# Again the initial build is fine
make -j2 main.bar
cat foo.h.in >foo.h || rm foo.h
yacc main.y
mv -f y.tab.c main.c
cat main.c foo.h >main.bar || rm main.bar
rm main.c
# But touch foo.h.in and things go wrong
touch foo.h.in
make -j2 main.bar
cat foo.h.in >foo.h || rm foo.h
cat main.c foo.h >main.bar || rm main.bar
cat: main.c: Aucun fichier ou dossier de ce type
# Here 'make -j2' decides to rebuild main.bar without first recreating
# main.c although we explicitly stated that main.bar depends on main.c.
# Here is what that command says with -d:
Considering target file `main.bar'.
Considering target file `main.y'. <--- Should be main.c
File `main.y' was considered already.
Considering target file `foo.h'.
File `foo.h' was considered already.
Pruning file `main.c'. <--- ???
Finished prerequisites of target file `main.bar'.
Prerequisite `main.c' of target `main.bar' does not exist. <--- !!!
Prerequisite `foo.h' is newer than target `main.bar'.
Must remake target `main.bar'.
cat main.c foo.h >main.bar || rm main.bar
cat: main.c: No such file or directory <--- Doh!
# The next attempt works though (but this time make does not have to
# rebuild foo.h)
make -j2 main.bar
yacc main.y
mv -f y.tab.c main.c
cat main.c foo.h >main.bar || rm main.bar
rm main.c
# Compare this with 'make -j1'
touch foo.h.in
make -j1 main.bar
cat foo.h.in >foo.h || rm foo.h
yacc main.y
mv -f y.tab.c main.c
cat main.c foo.h >main.bar || rm main.bar
rm main.c
# Here make correctly realizes it must rebuild main.c before attempting
# to run the command to generate main.bar. And the corresponding make
# -d output:
Prerequisite `foo.h.in' is newer than target `foo.h'.
Must remake target `foo.h'.
cat foo.h.in >foo.h || rm foo.h
Successfully remade target file `foo.h'.
Considering target file `main.c'. <--- Correct target
File `main.c' does not exist.
Pruning file `main.y'.
Finished prerequisites of target file `main.c'.
Must remake target `main.c'. <--- Yes!
yacc main.y
mv -f y.tab.c main.c
Must remake target `main.bar'.
cat main.c foo.h >main.bar || rm main.bar
Successfully remade target file `main.bar'.
Removing intermediate files...
rm main.c
It looks like make -j2 swapped main.c and main.y
--
Francois Gouget <[email protected]> http://fgouget.free.fr/
RFC 2549: ftp://ftp.isi.edu/in-notes/rfc2549.txt
IP over Avian Carriers with Quality of Service
--
To UNSUBSCRIBE, email to [email protected]
with a subject of "unsubscribe". Trouble? Contact [email protected]
