[LLVMdev] asan coverage

[Kostya Serebryany]

My slides from EuroLLVM regarding coverage, in case you are interested...
http://llvm.org/devmtg/2014-04/PDFs/LightningTalks/EuroLLVM'14%20--%20ASan%20%2B%20Coverage.pdf

--kcc


On Tue, Apr 1, 2014 at 2:13 AM, Duncan P. N. Exon Smith <
dexonsmith at apple.com> wrote:

>
> On Mar 31, 2014, at 10:45, Bob Wilson <bob.wilson at apple.com> wrote:
>
> >
> > On Mar 31, 2014, at 1:53 AM, Kostya Serebryany <kcc at google.com> wrote:
> >>
> >> This is what I see on 483.xalancbmk:
> >>  15 __llvm_prf_names 0036fcb0  00000000010abf40  00000000010abf40
>  00cabf40  2**5
> >>  16 __llvm_prf_data 001b77e0  000000000141bc00  000000000141bc00
>  0101bc00  2**5
> >>  32 __llvm_prf_cnts 00123468  0000000001af2fe0  0000000001af2fe0
>  014f2fe0  2**5
> >>
> >> __llvm_prf_names is larger than the other two combined.
> >> 483.xalancbmk is C++ and the function names are long. The same is true
> for most of the code we care about.
> >> Can't we use function PCs instead of function names in this table (and
> retrieve the function names from debug info)?
> >
> > That’s a bit surprising. We should check to make sure there isn’t
> anything obviously wrong.
>
> I'm surprised too, but it makes some sense.
>
>   - Most functions in the implementation details of the STL have long
> enough mangled
>     names (and little enough control flow) that the names would dominate
> the size
>     overhead.
>
>   - Many class member functions will have this property, too, like
> getters, setters,
>     and typical constructors, copy/move operators, and destructors.
>
> There's likely a way to emit these names more compactly using a tree (with
> links
> to parent nodes).
>
> Consider _ZN9Namespace5Class3fooEv, the mangled name for
> Namespace::Class::foo().
> We could do something like this:
>
>     %__llvm_profile_name = type {i8*, %__llvm_profile_name*}
>
>     @__llvm_profile_str__ZN = linkonce constant [4 x i8] c"_ZN\00"
>     @__llvm_profile_name__ZN = linkonce constant %__llvm_profile_name {
>       i8* getelementptr ([4 x i8]* @__llvm_profile_str__ZN, i32 0, i32 0),
>       %__llvm_profile_name* null }
>
>     @__llvm_profile_str_9Namespace = linkonce constant [11 x i8]
> c"9Namespace\00"
>     @__llvm_profile_name__ZN9Namespace = linkonce constant
> %__llvm_profile_name {
>       i8* getelementptr ([11 x i8]* @__llvm_profile_str_9Namespace, i32 0,
> i32 0),
>       %__llvm_profile_name* @__llvm_profile_name__ZN }
>
>     @__llvm_profile_str_5Class = linkonce constant [7 x i8] c"5Class\00"
>     @__llvm_profile_name__ZN9Namespace5Class = linkonce constant
>       %__llvm_profile_name {
>       i8* getelementptr ([7 x i8]* @__llvm_profile_str_5Class, i32 0, i32
> 0),
>       %__llvm_profile_name* @__llvm_profile_name__ZN9Namespace }
>
>     @__llvm_profile_str_3fooEv = linkonce constant [7 x i8] c"3fooEv\00"
>     @__llvm_profile_name__ZN9Namespace5Class3fooEv = linkonce constant
>       %__llvm_profile_name {
>       i8* getelementptr ([7 x i8]* @__llvm_profile_str_3fooEv, i32 0, i32
> 0),
>       %__llvm_profile_name* @__llvm_profile_name__ZN9Namespace5Class }
>
> Then _ZN9Namespace5Class3barEv (Namespace::Class::bar()) would be cheap.
>
>     @__llvm_profile_str_3barEv = linkonce constant [7 x i8] c"3barEv\00"
>     @__llvm_profile_name__ZN9Namespace5Class3barEv = linkonce constant
>       %__llvm_profile_name {
>       i8* getelementptr ([7 x i8]* @__llvm_profile_str_3barEv, i32 0, i32
> 0),
>       %__llvm_profile_name* @__llvm_profile_name__ZN9Namespace5Class }
>
> These would merge cleanly even between object files generated from
> different
> translation units.
>
> Doing it like that requires understanding the mangling and wouldn't
> compact common
> prefixes in C.  We could do something similar with a heuristic (split
> every 8
> characters), or split on common prefixes per translation unit (and hope
> they line up
> between translation units).
>
>
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