Assertion failed in transfer_fifo() Description of problem: In transfer_fifo(), fifo32_pop() fails since less than 32 bytes are in the fifo. Steps to reproduce: ``` export QEMU=/path/to/qemu-system-aarch64 cat << EOF | $QEMU \ -machine xlnx-zcu102 -monitor none -serial none \ -display none -nodefaults -qtest stdio -audio none writel 0xff070000 0x0f73720a writel 0xff07003c 0x1f37ee63 EOF ``` Additional information: ``` ==31717==WARNING: ASan doesn't fully support makecontext/swapcontext functions and may produce false positives in some cases! INFO: found LLVMFuzzerCustomMutator (0x55871da359f0). Disabling -len_control by default. INFO: Running with entropic power schedule (0xFF, 100). INFO: Seed: 1734665286 INFO: Loaded 1 modules (618606 inline 8-bit counters): 618606 [0x558720b94000, 0x558720c2b06e), INFO: Loaded 1 PC tables (618606 PCs): 618606 [0x558720222e60,0x558720b93540), /root/videzzo/videzzo_qemu/out-san/qemu-videzzo-aarch64-target-videzzo-fuzz-xlnx-zynqmp-can: Running 1 inputs 1 time(s) each. INFO: Reading pre_seed_input if any ... INFO: Executing pre_seed_input if any ... Matching objects by name , *xlnx.zynqmp-can* This process will fuzz the following MemoryRegions: * xlnx.zynqmp-can[1] (size 84) * xlnx.zynqmp-can[0] (size 84) * xlnx.zynqmp-can[1] (size 84) * xlnx.zynqmp-can[0] (size 84) This process will fuzz through the following interfaces: * clock_step, EVENT_TYPE_CLOCK_STEP, 0xffffffff +0xffffffff, 255,255 * xlnx.zynqmp-can, EVENT_TYPE_MMIO_READ, 0xff070000 +0x84, 4,4 * xlnx.zynqmp-can, EVENT_TYPE_MMIO_WRITE, 0xff070000 +0x84, 4,4 * xlnx.zynqmp-can, EVENT_TYPE_MMIO_READ, 0xff060000 +0x84, 4,4 * xlnx.zynqmp-can, EVENT_TYPE_MMIO_WRITE, 0xff060000 +0x84, 4,4 INFO: A corpus is not provided, starting from an empty corpus #2 INITED cov: 3 ft: 4 corp: 1/1b exec/s: 0 rss: 491Mb Running: poc-qemu-videzzo-aarch64-target-videzzo-fuzz-xlnx-zynqmp-can-crash-97ef02583c679111ba6ad823f573f139fac7c72e qemu-videzzo-aarch64-target-videzzo-fuzz-xlnx-zynqmp-can: ../util/fifo8.c:62: uint8_t fifo8_pop(Fifo8 *): Assertion `fifo->num > 0' failed. ==31717== ERROR: libFuzzer: deadly signal #0 0x558718e0e10e in __sanitizer_print_stack_trace /root/llvm-project/compiler-rt/lib/asan/asan_stack.cpp:86:3 #1 0x558718d5cd81 in fuzzer::PrintStackTrace() /root/llvm-project/compiler-rt/lib/fuzzer/FuzzerUtil.cpp:210:38 #2 0x558718d35cb6 in fuzzer::Fuzzer::CrashCallback() (.part.0) /root/llvm-project/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:236:18 #3 0x558718d35d82 in fuzzer::Fuzzer::CrashCallback() /root/llvm-project/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:208:1 #4 0x558718d35d82 in fuzzer::Fuzzer::StaticCrashSignalCallback() /root/llvm-project/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:207:19 #5 0x7f3ad4eba41f (/lib/x86_64-linux-gnu/libpthread.so.0+0x1441f) #6 0x7f3ad4ccc00a in __libc_signal_restore_set /build/glibc-SzIz7B/glibc-2.31/signal/../sysdeps/unix/sysv/linux/internal-signals.h:86:3 #7 0x7f3ad4ccc00a in raise /build/glibc-SzIz7B/glibc-2.31/signal/../sysdeps/unix/sysv/linux/raise.c:48:3 #8 0x7f3ad4cab858 in abort /build/glibc-SzIz7B/glibc-2.31/stdlib/abort.c:79:7 #9 0x7f3ad4cab728 in __assert_fail_base /build/glibc-SzIz7B/glibc-2.31/assert/assert.c:92:3 #10 0x7f3ad4cbcfd5 in __assert_fail /build/glibc-SzIz7B/glibc-2.31/assert/assert.c:101:3 #11 0x55871d6eeac9 in fifo8_pop /root/videzzo/videzzo_qemu/qemu/build-san-6/../util/fifo8.c:62:5 #12 0x55871a33f303 in fifo32_pop /root/videzzo/videzzo_qemu/qemu/include/qemu/fifo32.h:137:17 #13 0x55871a334bb5 in transfer_fifo /root/videzzo/videzzo_qemu/qemu/build-san-6/../hw/net/can/xlnx-zynqmp-can.c:455:23 #14 0x55871a32d4c0 in can_tx_post_write /root/videzzo/videzzo_qemu/qemu/build-san-6/../hw/net/can/xlnx-zynqmp-can.c:830:9 #15 0x558719393dcb in register_write /root/videzzo/videzzo_qemu/qemu/build-san-6/../hw/core/register.c:122:9 #16 0x558719397de8 in register_write_memory /root/videzzo/videzzo_qemu/qemu/build-san-6/../hw/core/register.c:203:5 #17 0x55871c9e9073 in memory_region_write_accessor /root/videzzo/videzzo_qemu/qemu/build-san-6/../softmmu/memory.c:492:5 #18 0x55871c9e89b1 in access_with_adjusted_size /root/videzzo/videzzo_qemu/qemu/build-san-6/../softmmu/memory.c:554:18 #19 0x55871c9e72d6 in memory_region_dispatch_write /root/videzzo/videzzo_qemu/qemu/build-san-6/../softmmu/memory.c:1514:16 #20 0x55871ca7548e in flatview_write_continue /root/videzzo/videzzo_qemu/qemu/build-san-6/../softmmu/physmem.c:2825:23 #21 0x55871ca635cb in flatview_write /root/videzzo/videzzo_qemu/qemu/build-san-6/../softmmu/physmem.c:2867:12 #22 0x55871ca63088 in address_space_write /root/videzzo/videzzo_qemu/qemu/build-san-6/../softmmu/physmem.c:2963:18 #23 0x558718e4e0cb in qemu_writel /root/videzzo/videzzo_qemu/qemu/build-san-6/../tests/qtest/videzzo/videzzo_qemu.c:1081:5 #24 0x558718e4c544 in dispatch_mmio_write /root/videzzo/videzzo_qemu/qemu/build-san-6/../tests/qtest/videzzo/videzzo_qemu.c:1222:28 #25 0x55871da313af in videzzo_dispatch_event /root/videzzo/videzzo.c:1122:5 #26 0x55871da2872b in __videzzo_execute_one_input /root/videzzo/videzzo.c:272:9 #27 0x55871da28600 in videzzo_execute_one_input /root/videzzo/videzzo.c:313:9 #28 0x558718e5510c in videzzo_qemu /root/videzzo/videzzo_qemu/qemu/build-san-6/../tests/qtest/videzzo/videzzo_qemu.c:1497:12 #29 0x55871da35c92 in LLVMFuzzerTestOneInput /root/videzzo/videzzo.c:1891:18 #30 0x558718d36826 in fuzzer::Fuzzer::ExecuteCallback(unsigned char*, unsigned long) /root/llvm-project/compiler-rt/lib/fuzzer/FuzzerLoop.cpp:594:17 #31 0x558718d19454 in fuzzer::RunOneTest(fuzzer::Fuzzer*, char const*, unsigned long) /root/llvm-project/compiler-rt/lib/fuzzer/FuzzerDriver.cpp:323:21 #32 0x558718d243fe in fuzzer::FuzzerDriver(int*, char***, int (*)(unsigned char*, unsigned long)) /root/llvm-project/compiler-rt/lib/fuzzer/FuzzerDriver.cpp:885:19 #33 0x558718d109e6 in main /root/llvm-project/compiler-rt/lib/fuzzer/FuzzerMain.cpp:20:30 #34 0x7f3ad4cad082 in __libc_start_main /build/glibc-SzIz7B/glibc-2.31/csu/../csu/libc-start.c:308:16 #35 0x558718d10a3d in _start (/root/videzzo/videzzo_qemu/out-san/qemu-videzzo-aarch64-target-videzzo-fuzz-xlnx-zynqmp-can+0x3291a3d) NOTE: libFuzzer has rudimentary signal handlers. Combine libFuzzer with AddressSanitizer or similar for better crash reports. SUMMARY: libFuzzer: deadly signal MS: 0 ; base unit: 0000000000000000000000000000000000000000 ```