[ASAN] fix startup crash in dlsym for long paths since glibc 2.27

Summary:
Error messages for dlsym used to be stored on the stack, but since
commit 2449ae7b ("ld.so: Introduce struct dl_exception") in glibc 2.27
these are now stored on the heap (and thus use the dlsym alloc pool).

Messages look like "undefined symbol: __isoc99_printf\0/path/to/a.out".
With many missing library functions and long object paths, the pool is
quickly exhausted. Implement a simple mechanism to return freed memory
to the pool (clear it in case it is used for calloc).

Fixes https://github.com/google/sanitizers/issues/957

Reviewed By: vitalybuka

Differential Revision: https://reviews.llvm.org/D47995

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@334703 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 7 insertions, 0 deletions

diff --git a/test/asan/TestCases/long-object-path.cc b/test/asan/TestCases/long-object-path.cc
new file mode 100644
index 000000000..592b0abb0
--- /dev/null
+++ b/test/asan/TestCases/long-object-path.cc
@@ -0,0 +1,7 @@
+// RUN: mkdir -p %T/a-long-directory-name-to-test-allocations-for-exceptions-in-_dl_lookup_symbol_x-since-glibc-2.27
+// RUN: %clangxx_asan -g %s -o %T/long-object-path
+// RUN: %run %T/a-*/../a-*/../a-*/../a-*/../a-*/../a-*/../a-*/../a-*/../long-object-path
+
+int main(void) {
+    return 0;
+}