[clang] [compiler-rt] [UBSan] Diagnose assumption violation (PR #104741)

[NAKAMURA Takumi via cfe-commits]

chapuni wrote:

This has triggered a failure in our private builder (aarch64-ubuntu20.04)

```
******************** TEST 'libFuzzer-aarch64-default-Linux :: strncmp.test' FAILED ********************
Exit Code: 1
Command Output (stderr):
--
RUN: at line 2: /home/bb/clang-aarch64/build/2/./bin/clang    -Wthread-safety -Wthread-safety-reference -Wthread-safety-beta   --driver-mode=g++ -O2 -gline-tables-only -fsanitize=address,fuzzer -I/home/bb/clang-aarch64/llvm-project/compiler-rt/lib/fuzzer  -Wthread-safety -Wthread-safety-reference -Wthread-safety-beta  /home/bb/clang-aarch64/llvm-project/compiler-rt/test/fuzzer/StrncmpTest.cpp -o /home/bb/clang-aarch64/build/2/projects/compiler-rt/test/fuzzer/AARCH64DefaultLinuxConfig/Output/strncmp.test.tmp-StrncmpTest
+ /home/bb/clang-aarch64/build/2/./bin/clang -Wthread-safety -Wthread-safety-reference -Wthread-safety-beta --driver-mode=g++ -O2 -gline-tables-only -fsanitize=address,fuzzer -I/home/bb/clang-aarch64/llvm-project/compiler-rt/lib/fuzzer -Wthread-safety -Wthread-safety-reference -Wthread-safety-beta /home/bb/clang-aarch64/llvm-project/compiler-rt/test/fuzzer/StrncmpTest.cpp -o /home/bb/clang-aarch64/build/2/projects/compiler-rt/test/fuzzer/AARCH64DefaultLinuxConfig/Output/strncmp.test.tmp-StrncmpTest
RUN: at line 3: not  /home/bb/clang-aarch64/build/2/projects/compiler-rt/test/fuzzer/AARCH64DefaultLinuxConfig/Output/strncmp.test.tmp-StrncmpTest              -seed=2 -runs=10000000   2>&1 | FileCheck /home/bb/clang-aarch64/llvm-project/compiler-rt/test/fuzzer/strncmp.test
+ not /home/bb/clang-aarch64/build/2/projects/compiler-rt/test/fuzzer/AARCH64DefaultLinuxConfig/Output/strncmp.test.tmp-StrncmpTest -seed=2 -runs=10000000
+ FileCheck /home/bb/clang-aarch64/llvm-project/compiler-rt/test/fuzzer/strncmp.test
/home/bb/clang-aarch64/llvm-project/compiler-rt/test/fuzzer/strncmp.test:4:8: error: CHECK: expected string not found in input
CHECK: BINGO
       ^
<stdin>:1:1: note: scanning from here
INFO: Running with entropic power schedule (0xFF, 100).
^
Input file: <stdin>
Check file: /home/bb/clang-aarch64/llvm-project/compiler-rt/test/fuzzer/strncmp.test
-dump-input=help explains the following input dump.
Input was:
<<<<<<
         1: INFO: Running with entropic power schedule (0xFF, 100). 
check:4     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
         2: INFO: Seed: 2 
check:4     ~~~~~~~~~~~~~~
         3: INFO: Loaded 1 modules (12 inline 8-bit counters): 12 [0xaaaaccfe3f00, 0xaaaaccfe3f0c),  
check:4     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
         4: INFO: Loaded 1 PC tables (12 PCs): 12 [0xaaaaccfe3f10,0xaaaaccfe3fd0),  
check:4     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
         5: INFO: -max_len is not provided; libFuzzer will not generate inputs larger than 4096 bytes 
check:4     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
         6: INFO: A corpus is not provided, starting from an empty corpus 
check:4     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
         .
         .
         .
>>>>>>
--
********************
```

https://github.com/llvm/llvm-project/pull/104741