Description
| Bugzilla Link | 43652 |
| Version | trunk |
| OS | Linux |
| CC | @jgalenson |
Extended Description
If I compile my program with ThinLTO and -fno-sanitize-cfi-canonical-jump-tables, I cannot make an indirect call to a function alias. I can reproduce the issue as follows:
$ cat test.c
#include <stdio.h>
typedef int (*func_t)(int);
int a(int n)
{
return 1;
}
int b(int n) attribute((alias("a")));
int main()
{
func_t f[] = { a, b, NULL };
for (int i = 0; f[i] != NULL; i++) {
printf("calling %016lx\n", (unsigned long)f[i]);
printf("\t-> %d\n", f[i](0));
}
return 0;
}
I would expect indirect calls to both a and b work fine with CFI, as seen here:
$ clang -flto=thin -fuse-ld=lld -fvisibility=default -fsanitize=cfi test.c
$ ./a.out
calling 00000000002017b0
-> 1
calling 00000000002017b0
-> 1
However, if I enable -fno-sanitize-cfi-canonical-jump-tables, the test program fails to compile:
$ clang -flto=thin -fuse-ld=lld -fvisibility=default -fsanitize=cfi -fno-sanitize-cfi-canonical-jump-tables test.c
ld.lld: error: undefined symbol: a
referenced by ld-temp.o
lto.tmp:(a.cfi_jt)
clang-10: error: linker command failed with exit code 1 (use -v to see invocation)
Adding -fsanitize-cfi-cross-dso allows me to compile the program again, but it now trips CFI:
$ clang -flto=thin -fuse-ld=lld -fvisibility=default -fsanitize=cfi -fno-sanitize-cfi-canonical-jump-tables -fsanitize-cfi-cross-dso test.c
$ ./a.out
calling 00005648c2aab030
-> 1
calling 00005648c2aab040
Illegal instruction
Looking at a.out, we have:
1125: 0000000000029030 8 FUNC LOCAL HIDDEN 14 a.cfi_jt
1204: 0000000000029040 14 FUNC GLOBAL DEFAULT 14 a
1207: 0000000000029040 14 FUNC GLOBAL DEFAULT 14 b
Which means the alias points directly to a, instead of a.cfi_jt. Switching to -flto works though:
$ clang -flto -fuse-ld=lld -fvisibility=default -fsanitize=cfi -fno-sanitize-cfi-canonical-jump-tables -fsanitize-cfi-cross-dso test.c
$ ./a.out
calling 0000563f82e14030
-> 1
calling 0000563f82e14030
-> 1
This is currently reproducible with ToT LLVM:
$ clang --version | head -n1
clang version 10.0.0 (https://github.com/llvm/llvm-project.git b95d4c3)
$ ld.lld --version
LLD 10.0.0 (https://github.com/llvm/llvm-project.git b95d4c3) (compatible with GNU linkers)