Messages in this thread | | | Date | Tue, 12 Mar 2019 23:18:53 +0300 | From | Alexey Dobriyan <> | Subject | Re: [PATCH] Drop -Wdeclaration-after-statement |
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On Tue, Mar 12, 2019 at 12:50:17PM -0700, Andrew Morton wrote: > On Tue, 12 Mar 2019 20:24:47 +0300 Alexey Dobriyan <adobriyan@gmail.com> wrote: > > > On Mon, Mar 11, 2019 at 05:38:45PM -0700, Andrew Morton wrote: > > > On Sun, 10 Mar 2019 16:35:35 +0300 Alexey Dobriyan <adobriyan@gmail.com> wrote: > > > > > > > Newly added static_assert() is formally a declaration, which will give > > > > a warning if used in the middle of the function. > > > > > > > > ... > > > > > > > > --- a/Makefile > > > > +++ b/Makefile > > > > @@ -792,9 +792,6 @@ endif > > > > # arch Makefile may override CC so keep this after arch Makefile is included > > > > NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include) > > > > > > > > -# warn about C99 declaration after statement > > > > -KBUILD_CFLAGS += -Wdeclaration-after-statement > > > > - > > > > # Variable Length Arrays (VLAs) should not be used anywhere in the kernel > > > > KBUILD_CFLAGS += $(call cc-option,-Wvla) > > > > > > I do wish your changelogs were more elaborate :( > > > > > So the proposal is to disable -Wdeclaration-after-statement in all > > > cases for all time because static_assert() doesn't work correctly? > > > > Yes. I converted 2 cases in /proc to static_assert() and you can't write > > > > { > > [code] > > static_assert() > > } > > > > without a warning because static_assert() is declaration. > > So people would move BUILD_BUG_ON() to where it doesn't belong. > > Sure. > > > > Surely there's something we can do to squish the static_assert() issue > > > while retaining -Wdeclaration-after-statement? > > > > It is not good in my opinion to stick to -Wdeclaration-after-statement. > > Why?
It is useful to have declarations mixed with code. It reduces effective scope of a variable:
int a; [a misused] ... [a used correctly]
vs
[a misused -- compile error] ... int a; [a used correctly]
It is possible to partially workaround that but at the cost of a indentation level. I'll post the following patch soon:
- NEW_AUX_ENT(AT_UID, from_kuid_munged(cred->user_ns, cred->uid)); - NEW_AUX_ENT(AT_EUID, from_kuid_munged(cred->user_ns, cred->euid)); - NEW_AUX_ENT(AT_GID, from_kgid_munged(cred->user_ns, cred->gid)); - NEW_AUX_ENT(AT_EGID, from_kgid_munged(cred->user_ns, cred->egid)); + { + const struct cred *cred = current_cred(); + struct user_namespace *user_ns = cred->user_ns; + + NEW_AUX_ENT(AT_UID, from_kuid_munged(user_ns, cred->uid)); + NEW_AUX_ENT(AT_EUID, from_kuid_munged(user_ns, cred->euid)); + NEW_AUX_ENT(AT_GID, from_kgid_munged(user_ns, cred->gid)); + NEW_AUX_ENT(AT_EGID, from_kgid_munged(user_ns, cred->egid)); + }
Often it is simply not possible to shift big function one level deeper.
Another related thing, C99 has this very cool feature of per-for-loop declarations:
for (int i = 0; ...)
Once kernel will switch to C99 or C11 it _will_ be used to the point of requiring it on the coding style level. The superstition of declaring everything in the beginning of a function will fall, so might as well start earlier.
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