[PATCH] D30423: [ubsan] Detect UB loads from bitfields

[Jonathan Roelofs via Phabricator via cfe-commits]

jroelofs accepted this revision.
jroelofs added a comment.
This revision is now accepted and ready to land.

LGTM



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Comment at: test/CodeGenObjC/ubsan-bool.m:26
+  // OBJC:  [[ICMP:%.*]] = icmp ule i8 [[ASHR]], 1, !nosanitize
+  // OBJC: call void @__ubsan_handle_load_invalid_value
+
----------------
vsk wrote:
> jroelofs wrote:
> > vsk wrote:
> > > arphaman wrote:
> > > > Is it possible to avoid the check here since the bitfield is just one bit wide?
> > > No, a user could do:
> > > 
> > > ```
> > > struct S1 s;
> > > s.b1 = 1;
> > > if (s.b1 == 1) // evaluates to false, s.b1 is negative
> > > ```
> > > 
> > > With this patch we get:
> > > ```
> > > runtime error: load of value -1, which is not a valid value for type 'BOOL' (aka 'signed char')
> > > ```
> > What if BOOL is an `unsigned char`, or a `char` that's not signed?
> Good point, we don't need to emit the range check if the bitfield is an unsigned, 1-bit wide BOOL. Would you be OK with me tackling that in a follow-up patch?
No problem, sounds good to me.


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Comment at: test/CodeGenObjC/ubsan-bool.m:50
+// OBJC: [[SHL:%.*]] = shl i8 [[LOAD]], 7
+// OBJC: [[ASHR:%.*]] = ashr i8 [[SHL]], 7
+// OBJC: icmp ule i8 [[ASHR]], 1, !nosanitize
----------------
hmmm. just occurred to me that this value is always going to be 0xff or 0x0, so it might be useful if there were also a frontend warning that complains about signed bitfield bools (maybe something useful for another patch).


https://reviews.llvm.org/D30423