On 6/8/20 9:56 PM, Marco Elver wrote:
On Mon, 8 Jun 2020 at 19:32, Martin Liška <mli...@suse.cz> wrote:
On 6/3/20 9:23 PM, Marco Elver wrote:
On Wed, 03 Jun 2020, Borislav Petkov wrote:
On Thu, May 14, 2020 at 12:05:38PM +0100, Will Deacon wrote:
Talking off-list, Clang >= 7 is pretty reasonable wrt inlining decisions
and the behaviour for __always_inline is:
* An __always_inline function inlined into a __no_sanitize function is
not instrumented
* An __always_inline function inlined into an instrumented function is
instrumented
* You can't mark a function as both __always_inline __no_sanitize, because
__no_sanitize functions are never inlined
GCC, on the other hand, may still inline __no_sanitize functions and then
subsequently instrument them.
Yeah, about that: I've been looking for a way to trigger this so that
I can show preprocessed source to gcc people. So do you guys have a
.config or somesuch I can try?
For example take this:
int x;
static inline __attribute__((no_sanitize_thread)) void
do_not_sanitize(void) {
x++;
}
void sanitize_this(void) {
do_not_sanitize();
}
Then
gcc-10 -O3 -fsanitize=thread -o example.o -c example.c
objdump -D example.o
Hello.
Thank you for the example. It seems to me that Clang does not inline a
no_sanitize_* function
into one which is instrumented. Is it a documented behavior ([1] doesn't
mention that)?
If so, we can do the same in GCC.
It is not explicitly mentioned in [1]. But the contract of
"no_sanitize" is "that a particular instrumentation or set of
instrumentations should not be applied". That contract is broken if a
function is instrumented, however that may happen. It sadly does
happen with GCC when a function is inlined. Presumably because the
sanitizer passes for TSAN/ASAN/MSAN run after the optimizer -- this
definitely can't change. Also because it currently gives us the
property that __always_inline functions are instrumented according to
the function they are inlined into (a property we want).
The easy fix to no_sanitize seems to be to do what Clang does, and
never inline no_sanitize functions (with or without "inline"
attribute). always_inline functions should remain unchanged
(specifying no_sanitize on an always_inline function is an error).
Hello.
Works for me and I've just sent patch for that:
https://gcc.gnu.org/pipermail/gcc-patches/2020-June/547618.html
Note this applies to all sanitizers (TSAN/ASAN/MSAN) and their
no_sanitize attribute that GCC has.
Sure.
The list of requirements were also summarized in more detail here:
https://lore.kernel.org/lkml/CANpmjNMTsY_8241bS7=xafqvzhflrvekv_um4aduwe_kh3r...@mail.gmail.com/
Hope that makes sense. (I also need to send a v2 for param
tsan-distinguish-volatile, but haven't gotten around to it yet --
hopefully soon.
The patch is approved now.
And then we also need a param
tsan-instrument-func-entry-exit, which LLVM has for TSAN. One step at
a time though.)
Yes, please send a patch for it.
Martin
Thanks,
-- Marco
Thanks,
Martin
[1] https://clang.llvm.org/docs/AttributeReference.html#no-sanitize
will show that do_not_sanitize() was inlined into sanitize_this() and is
instrumented. (With Clang this doesn't happen.)
Hope this is enough.
Thanks,
-- Marco
