On Tue, Sep 29, 2020 at 1:47 PM Arvind Sankar <nivedita@xxxxxxxxxxxx> wrote: > > On Tue, Sep 29, 2020 at 01:30:22PM -0700, Nick Desaulniers wrote: > > On Tue, Sep 29, 2020 at 1:25 PM Nick Desaulniers > > <ndesaulniers@xxxxxxxxxx> wrote: > > > > > > On Tue, Sep 29, 2020 at 1:08 PM Arvind Sankar <nivedita@xxxxxxxxxxxx> wrote: > > > > > > > > On Tue, Sep 29, 2020 at 12:43:18PM -0700, Nick Desaulniers wrote: > > > > > The stringification operator, `#`, in the preprocessor escapes strings. > > > > > For example, `# "foo"` becomes `"\"foo\""`. GCC and Clang differ in how > > > > > they treat section names that contain \". > > > > > > > > > > The portable solution is to not use a string literal with the > > > > > preprocessor stringification operator. > > > > > > > > > > In this case, since __section unconditionally uses the stringification > > > > > operator, we actually want the more verbose > > > > > __attribute__((__section__())). > > > > > > > > > > Link: https://bugs.llvm.org/show_bug.cgi?id=42950 > > > > > Fixes: commit e04462fb82f8 ("Compiler Attributes: remove uses of __attribute__ from compiler.h") > > > > > Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > > > > > --- > > > > > include/linux/compiler.h | 2 +- > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > diff --git a/include/linux/compiler.h b/include/linux/compiler.h > > > > > index 92ef163a7479..ac45f6d40d39 100644 > > > > > --- a/include/linux/compiler.h > > > > > +++ b/include/linux/compiler.h > > > > > @@ -155,7 +155,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val, > > > > > extern typeof(sym) sym; \ > > > > > static const unsigned long __kentry_##sym \ > > > > > __used \ > > > > > - __section("___kentry" "+" #sym ) \ > > > > > + __attribute__((__section__("___kentry+" #sym))) \ > > > > > = (unsigned long)&sym; > > > > > #endif > > > > > > > > > > -- > > > > > 2.28.0.709.gb0816b6eb0-goog > > > > > > > > > > > > > There was this previous mini-thread: > > > > https://lore.kernel.org/lkml/20200629205448.GA1474367@xxxxxxxxxxxxxxxxxx/ > > > > and this older one: > > > > https://lore.kernel.org/lkml/20190904181740.GA19688@xxxxxxxxx/ > > > > > > > > Just for my own curiosity: how does KENTRY actually get used? grep > > > > doesn't show any hits, and the thread from 2019 was actually going to > > > > drop it if I read it right, and also just remove stringification from > > > > the __section macro. > > > > > > Oh, sorry I didn't respond on that thread; I could have sworn I ran a > > > grep for KENTRY back then. > > > > > > $ git log -S KENTRY > > > > Added by > > b67067f1176df6ee727450546b58704e4b588563 ? > > > > Yeah but nothing seems to have used it. I assume for LTO we use some > other technique to mark functions as used? Nicholas, do you recall why KENTRY was added in b67067f1176df6ee727450546b58704e4b588563? May I remove that and the addition to INIT_DATA from that commit? -- Thanks, ~Nick Desaulniers
