URL:
<http://savannah.gnu.org/bugs/?26864>
Summary: make -j2 fails to rebuild intermediate file
Project: make
Submitted by: srivasta
Submitted on: Sun 21 Jun 2009 12:04:03 PM CDT
Severity: 3 - Normal
Item Group: Bug
Status: None
Privacy: Public
Assigned to: None
Open/Closed: Open
Discussion Lock: Any
Component Version: 3.81
Operating System: POSIX-Based
Fixed Release: None
_______________________________________________________
Details:
This was reported by a Debian user. Here is how to reproduce the
problem:
cat >Makefile <<"EOF"
# .bar files depend on .c files as well as foo.h
%.bar: %.c foo.h
cat $^ >$@ || rm $@
# foo.h is created from foo.in
foo.h: foo.h.in
cat $^ >$@ || rm $@
# main.c should be created from main.y below
EOF
cat >main.y <"EOF"
%%
command:
"q" { return 1; }
;
%%
EOF
echo bar >foo.h.in
# 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: No such file or directory
# 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
I can't get around the fact that there is a reproducible
difference based on whether or not the -j2 argument was give,
manoj
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