On Mon, Jul 30, 2018 at 1:01 PM Nathan Chancellor <natechancellor@xxxxxxxxx> wrote: > > On Mon, Jul 30, 2018 at 12:48:06PM -0700, Nick Desaulniers wrote: > > On Mon, Jul 30, 2018 at 11:39 AM Nathan Chancellor > > <natechancellor@xxxxxxxxx> wrote: > > > > > > On Mon, Jul 30, 2018 at 10:06:20AM -0700, Nick Desaulniers wrote: > > > > Starting with Clang-7.0, _THIS_IP_ generates -Wreturn-stack-address > > > > warnings for almost every translation unit. In general, I'd prefer to > > > > leave this on (returning the address of a stack allocated variable is in > > > > general a bad idea) and disable it only at whitelisted call sites. > > > > > > > > We can't do something like: > > > > #pragma clang diagnostic push > > > > #pragma clang diagnostic ignored "-Wreturn-stack-address" > > > > <code> > > > > #pragma clang diagnostic pop > > > > > > > > in a GNU Statement Expression or macro, hence we use _Pragma, which is > > > > its raison d'être: https://gcc.gnu.org/onlinedocs/cpp/Pragmas.html > > > > > > > > Cc: stable@xxxxxxxxxxxxxxx # 4.17, 4.14, 4.9, 4.4 > > > > Signed-off-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> > > > > --- > > > > include/linux/kernel.h | 10 +++++++++- > > > > 1 file changed, 9 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/include/linux/kernel.h b/include/linux/kernel.h > > > > index 941dc0a5a877..5906f5727f90 100644 > > > > --- a/include/linux/kernel.h > > > > +++ b/include/linux/kernel.h > > > > @@ -168,7 +168,15 @@ > > > > > > > > > > > > #define _RET_IP_ (unsigned long)__builtin_return_address(0) > > > > -#define _THIS_IP_ ({ __label__ __here; __here: (unsigned long)&&__here; }) > > > > +#define _THIS_IP_ ( \ > > > > +{ \ > > > > + _Pragma("clang diagnostic push") \ > > > > + _Pragma("clang diagnostic ignored \"-Wreturn-stack-address\"") \ > > > > + __label__ __here; \ > > > > +__here: (unsigned long)&&__here; \ > > > > + _Pragma("clang diagnostic pop") \ > > > > +} \ > > > > +) > > > > > > > > #ifdef CONFIG_LBDAF > > > > # include <asm/div64.h> > > > > -- > > > > 2.18.0.233.g985f88cf7e-goog > > > > > > > > > > This generates a ton of warnings with GCC: > > > > > > In file included from ./include/linux/spinlock.h:58, > > > from ./include/linux/mmzone.h:8, > > > from ./include/linux/gfp.h:6, > > > from ./include/linux/slab.h:15, > > > from ./include/linux/crypto.h:24, > > > from arch/x86/kernel/asm-offsets.c:9: > > > ./include/linux/bottom_half.h: In function ‘local_bh_disable’: > > > ./include/linux/bottom_half.h:19: error: ignoring #pragma clang diagnostic [-Werror=unknown-pragmas] > > > __local_bh_disable_ip(_THIS_IP_, SOFTIRQ_DISABLE_OFFSET); > > > > > > ./include/linux/bottom_half.h:19: error: ignoring #pragma clang diagnostic [-Werror=unknown-pragmas] > > > ./include/linux/bottom_half.h:19: error: ignoring #pragma clang diagnostic [-Werror=unknown-pragmas] > > > ./include/linux/bottom_half.h: In function ‘local_bh_enable’: > > > ./include/linux/bottom_half.h:32: error: ignoring #pragma clang diagnostic [-Werror=unknown-pragmas] > > > __local_bh_enable_ip(_THIS_IP_, SOFTIRQ_DISABLE_OFFSET); > > > > > > ./include/linux/bottom_half.h:32: error: ignoring #pragma clang diagnostic [-Werror=unknown-pragmas] > > > ./include/linux/bottom_half.h:32: error: ignoring #pragma clang diagnostic [-Werror=unknown-pragmas] > > > cc1: all warnings being treated as errors > > > make[1]: *** [Kbuild:56: arch/x86/kernel/asm-offsets.s] Error 1 > > > make: *** [Makefile:1081: prepare0] Error 2 > > > > Ah, good catch. I thought I had tested locally with gcc-8, but it > > seems that it was likely only godbolt. I do see the errors locally > > when building with gcc-8. > > > > > > > > A proper solution is probably going to involve what was done for the > > > -Wattribute-alias warnings from GCC 8 in commits 8793bb7f4a9d ("kbuild: > > > add macro for controlling warnings to linux/compiler.h") and > > > bee20031772a ("disable -Wattribute-alias warning for SYSCALL_DEFINEx()") > > > > > > I'll take a look at it in a bit unless someone beats me to it. > > > > I'll fix this up, triple check with gcc-8, and attribute you in the > > Suggested-by tag. Thank you for verifying. > > -- > > Thanks, > > ~Nick Desaulniers > > I forgot to mention there is a similar macro that will need this same > fix in arch/arm64/include/asm/processor.h (current_text_addr), if you > want to tackle it in v2. Do CC me on the next series so that I can test, > thank you for doing this! !!! $ grep -R current_text_addr shows many definitions of current_text_addr per arch/ that are all essentially the same, and very very few uses of it. I prefer to consolidate current_text_addr() in a follow up series, since a common definition with per-arch overrides will have to get a lot of sign offs. Though, for arm64, a simple: -#define current_text_addr() ({ __label__ _l; _l: &&_l;}) +#define current_text_addr() _THIS_IP_ does the trick, it would be better to have a single shared definition. -- Thanks, ~Nick Desaulniers
