[LLVMdev] Global constructors "get lost" when transforming bitcode files

[Jonas Wagner]

Hello,

A strange problem appears when upgrading from release_34 to testing. Some
transformations to bitcode files cause registered global_ctors to not be
called. Here's an example (I've also attached the complete example and
pasted it below):

This works:

    clang -fsanitize=address  -flto -c -o sum.o sum.c
    clang -fsanitize=address -o sum sum.o

This doesn't work:

    clang -fsanitize=address  -flto -c -o sum.o sum.c
    llvm-dis sum.o
    llvm-as sum.o.ll -o sum.o
    clang -fsanitize=address -o sum sum.o

The second version segfaults when accessing shadow memory, because the
memory has not been initialized, because __asan_init_* was never called.
This is surprising, because in the llvm-disassembly the global constructor
still shows up.

The llvm-dis/llvm-as operation should be a no-op, yet the global_ctors get
lost in the process. This happens also with other operations that affect
global_ctors, e.g., with "opt -insert-gcov-profiling".

The problem does not occur in the release_34 branch, but I have seen it on
both testing and master.

Any idea where this could come from would be much appreciated!
Jonas


testcase:

cat >sum.c <<EOF
#include <stdio.h>
#include <assert.h>

int main() {
    const int MAX_SIZE = 100;
    int a[MAX_SIZE];

    for (int i = 0; i < MAX_SIZE; ++i) {
        a[i] = i * i + 4;
    }

    int n_numbers;
    printf("How many numbers should I sum up? ");
    scanf("%d", &n_numbers);

    int sum = 0;
    for (int i = 0; i < n_numbers; ++i) {
        sum += a[i];
    }

    assert(sum >= 0);
    printf("The sum is: %d\n", sum);
    return 0;
}
EOF

set -ex
rm -f *.o *.ll sum

clang -fsanitize=address  -flto -c -o sum.o sum.c

llvm-dis sum.o
llvm-as sum.o.ll -o sum.o

clang -fsanitize=address -o sum sum.o

echo 22 | ./sum
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