[compiler-rt] r204823 - Avoid aliases to weak aliases in interceptors.

[Rafael Espindola]

Author: rafael
Date: Wed Mar 26 10:48:59 2014
New Revision: 204823

URL: http://llvm.org/viewvc/llvm-project?rev=204823&view=rev
Log:
Avoid aliases to weak aliases in interceptors.

The interceptors had code that after macro expansion ended up looking like

extern "C" void memalign()
    __attribute__((weak, alias("__interceptor_memalign")));
extern "C" void __interceptor_memalign() {}
extern "C" void __interceptor___libc_memalign()
    __attribute__((alias("memalign")));

That is,
* __interceptor_memalign is a function
* memalign is a weak alias to __interceptor_memalign
* __interceptor___libc_memalign is an alias to memalign

Both gcc and clang produce assembly that look like

__interceptor_memalign:
...
        .weak   memalign
memalign = __interceptor_memalign
        .globl  __interceptor___libc_memalign
__interceptor___libc_memalign = memalign

What it means in the end is that we have 3 symbols pointing to the
same position in the file, one of which is weak:

     8: 0000000000000000     1 FUNC    GLOBAL DEFAULT    1
__interceptor_memalign
     9: 0000000000000000     1 FUNC    WEAK   DEFAULT    1 memalign
    10: 0000000000000000     1 FUNC    GLOBAL DEFAULT    1
__interceptor___libc_memalign

In particular, note that __interceptor___libc_memalign will always
point to __interceptor_memalign, even if we do link in a strong symbol
for memalign. In fact, the above code produces exactly the same binary
as

extern "C" void memalign()
    __attribute__((weak, alias("__interceptor_memalign")));
extern "C" void __interceptor_memalign() {}
extern "C" void __interceptor___libc_memalign()
    __attribute__((alias("__interceptor_memalign")));

If nothing else, this patch makes it more obvious what is going on.

Modified:
    compiler-rt/trunk/lib/lsan/lsan_interceptors.cc
    compiler-rt/trunk/lib/msan/msan_interceptors.cc

Modified: compiler-rt/trunk/lib/lsan/lsan_interceptors.cc
URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/lsan/lsan_interceptors.cc?rev=204823&r1=204822&r2=204823&view=diff
==============================================================================
--- compiler-rt/trunk/lib/lsan/lsan_interceptors.cc (original)
+++ compiler-rt/trunk/lib/lsan/lsan_interceptors.cc Wed Mar 26 10:48:59 2014
@@ -152,7 +152,7 @@ INTERCEPTOR(void*, pvalloc, uptr size) {
   return Allocate(stack, size, GetPageSizeCached(), kAlwaysClearMemory);
 }
 
-INTERCEPTOR(void, cfree, void *p) ALIAS("free");
+INTERCEPTOR(void, cfree, void *p) ALIAS(WRAPPER_NAME(free));
 
 #define OPERATOR_NEW_BODY                              \
   ENSURE_LSAN_INITED;                                  \
@@ -185,7 +185,8 @@ void operator delete[](void *ptr, std::n
 
 // We need this to intercept the __libc_memalign calls that are used to
 // allocate dynamic TLS space in ld-linux.so.
-INTERCEPTOR(void *, __libc_memalign, uptr align, uptr s) ALIAS("memalign");
+INTERCEPTOR(void *, __libc_memalign, uptr align, uptr s)
+    ALIAS(WRAPPER_NAME(memalign));
 
 ///// Thread initialization and finalization. /////
 

Modified: compiler-rt/trunk/lib/msan/msan_interceptors.cc
URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/msan/msan_interceptors.cc?rev=204823&r1=204822&r2=204823&view=diff
==============================================================================
--- compiler-rt/trunk/lib/msan/msan_interceptors.cc (original)
+++ compiler-rt/trunk/lib/msan/msan_interceptors.cc Wed Mar 26 10:48:59 2014
@@ -161,8 +161,8 @@ INTERCEPTOR(void *, memalign, SIZE_T bou
   return ptr;
 }
 
-INTERCEPTOR(void*, __libc_memalign, uptr align, uptr s)
-  ALIAS("memalign");
+INTERCEPTOR(void *, __libc_memalign, uptr align, uptr s)
+    ALIAS(WRAPPER_NAME(memalign));
 
 INTERCEPTOR(void *, valloc, SIZE_T size) {
   GET_MALLOC_STACK_TRACE;