https://bugs.llvm.org/show_bug.cgi?id=48635
Bug ID: 48635
Summary: cfi, cross-dso, wrong operation of
-fno-sanitize-cfi-cross-dso
Product: new-bugs
Version: 11.0
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: new bugs
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
Created attachment 24328
--> https://bugs.llvm.org/attachment.cgi?id=24328&action=edit
Reproducible example
Clang compiler doesn't ignore cross-dso calls for the following conditions:
- CFI is enabled;
- -fno-sanitize-cfi-cross-dso is used;
- optimization level is -O2;
- LLVM's ld.lld linker is used.
"Compiler-time" problem rises if one try to execute the function from the
shared object (.so) from the other executable binary (main).
Instead, compiler generates binary code with undefined instruction on the place
where cross-dso is used, for example:
```
int exec_func_from_dso(void)
{
fptr_t fptr = get_fptr();
201751: e8 5a 00 00 00 callq 2017b0 <get_fptr@plt>
fptr();
201756: 0f 0b ud2
```
At the same time, there is no problem with the source code (please, see
attached cfi_cross_dso_problem_report.tar).
Clang's help says:
```
-fno-sanitize-cfi-cross-dso
Disable control flow integrity (CFI) checks for cross-DSO calls.
```
As a user of the Clang I understand that if to use
"-fno-sanitize-cfi-cross-dso", cross-dso places will not be taken into account
during CFI operation (compilation and run-time execution).
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