| Message ID | 20180718091336.4540-1-dirk@gouders.net (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
2018-07-18 18:13 GMT+09:00 Dirk Gouders <dirk@gouders.net>: > Users of if_changed could easily feel invited to use it to divide a > recipe into parts like: > > a: prereq FORCE > $(call if_changed,do_a) > $(call if_changed,do_b) > > But this is problematic, because if_changed should not be used more > than once per target: in the above example, if_changed stores the > command-line of the given command in .a.cmd and when a is up-to-date > with respect to prereq, the file .a.cmd contains the command-line for > the last command executed, i.e. do_b. > > When the recipe is then executed again, without any change of > prerequisites, the command-line check for do_a will fail, do_a will be > executed and stored in .a.cmd. The next check, however, will still see > the old content (the file isn't re-read) and if_changed will skip > do_b, because the command-line test will not recognize a change. On > the next execution of the recipe the roles will flip: do_a is OK but > do_b not and it will be executed. And so on... > > Signed-off-by: Dirk Gouders <dirk@gouders.net> > --- Applied. Thanks! > Documentation/kbuild/makefiles.txt | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt > index 048fc39a6b91..01fae5a01ce7 100644 > --- a/Documentation/kbuild/makefiles.txt > +++ b/Documentation/kbuild/makefiles.txt > @@ -1105,6 +1105,12 @@ When kbuild executes, the following steps are followed (roughly): > target: source(s) FORCE > #WRONG!# $(call if_changed, ld/objcopy/gzip/...) > > + Note: if_changed should not be used more than once per target. > + It stores the executed command in a corresponding .cmd > + file and multiple calls would result in overwrites and > + unwanted results when the target is up to date and only the > + tests on changed commands trigger execution of commands. > + > ld > Link target. Often, LDFLAGS_$@ is used to set specific options to ld. > > -- > 2.16.1 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kbuild" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/Documentation/kbuild/makefiles.txt b/Documentation/kbuild/makefiles.txt index 048fc39a6b91..01fae5a01ce7 100644 --- a/Documentation/kbuild/makefiles.txt +++ b/Documentation/kbuild/makefiles.txt @@ -1105,6 +1105,12 @@ When kbuild executes, the following steps are followed (roughly): target: source(s) FORCE #WRONG!# $(call if_changed, ld/objcopy/gzip/...) + Note: if_changed should not be used more than once per target. + It stores the executed command in a corresponding .cmd + file and multiple calls would result in overwrites and + unwanted results when the target is up to date and only the + tests on changed commands trigger execution of commands. + ld Link target. Often, LDFLAGS_$@ is used to set specific options to ld.
Users of if_changed could easily feel invited to use it to divide a recipe into parts like: a: prereq FORCE $(call if_changed,do_a) $(call if_changed,do_b) But this is problematic, because if_changed should not be used more than once per target: in the above example, if_changed stores the command-line of the given command in .a.cmd and when a is up-to-date with respect to prereq, the file .a.cmd contains the command-line for the last command executed, i.e. do_b. When the recipe is then executed again, without any change of prerequisites, the command-line check for do_a will fail, do_a will be executed and stored in .a.cmd. The next check, however, will still see the old content (the file isn't re-read) and if_changed will skip do_b, because the command-line test will not recognize a change. On the next execution of the recipe the roles will flip: do_a is OK but do_b not and it will be executed. And so on... Signed-off-by: Dirk Gouders <dirk@gouders.net> --- Documentation/kbuild/makefiles.txt | 6 ++++++ 1 file changed, 6 insertions(+)