http://llvm.org/bugs/show_bug.cgi?id=20085
Bug ID: 20085
Summary: asan should not instrument loads generated by ubsan
Product: new-bugs
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: new bugs
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected],
[email protected], [email protected]
Classification: Unclassified
% cat vptr.cc
struct A { virtual void f(); };
void Bar(A *a) { a->f(); }
% clang -S -O -fsanitize=vptr -o - vptr.cc| grep
'call.*\(__ubsan\|__asan_report\)'
callq __ubsan_handle_dynamic_type_cache_miss
% clang -S -O -fsanitize=address -o - vptr.cc| grep
'call.*\(__ubsan\|__asan_report\)'
callq __asan_report_load8
callq __asan_report_load8
% clang -S -O -fsanitize=address,vptr -o - vptr.cc| grep
'call.*\(__ubsan\|__asan_report\)'
callq __asan_report_load8
callq __asan_report_load8
callq __asan_report_load8
callq __ubsan_handle_dynamic_type_cache_miss
%
As you can see, asan instruments one load generated by ubsan.
This is redundant.
One way to avoid this extra instrumentation is to attach some kind of metadata
to the load and honor it in asan instrumentation pass.
We do something similar in tsan to treat vptr loads in a special way:
clang -S -O -fsanitize=thread -emit-llvm -o - vptr.cc
%vtable = load void (%struct.A*)*** %0, !tbaa !1
!1 = metadata !{metadata !2, metadata !2, i64 0}
!2 = metadata !{metadata !"vtable pointer", metadata !3, i64 0}
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