Test case `nyancat` doesn't work well on the latest rv32emu.

[qwe661234]

Recently, I checked out the latest commit (40fcbfe), and I found that the nyancat test case doesn't work as well as it used to, both in JIT and non-JIT mode. It’s possible that some instructions implementation or refinement is impacting this test case.

Reproducer

make ENABLE_JIT=0 clean all
./build/rv32emu ./build/riscv32/nyancat

The test case displays a static image without any animation.

[visitorckw]

I have successfully bisected the issue, and the regression appears to be introduced in commit a6ecb0c ("Bring up Linux kernel"). You can find the full bisect log below:

a6ecb0c4e9bb06c6348d51dfa2bc2aa8a602d2b1 is the first bad commit
commit a6ecb0c4e9bb06c6348d51dfa2bc2aa8a602d2b1 (HEAD)
Author: ChinYikMing <yikming2222@gmail.com>
Date:   Sun Dec 15 00:02:05 2024 +0800

    Bring up Linux kernel
    
    The 8250 UART and PLIC peripherals, defined in src/devices/uart.[ch]
    and src/devices/plic.[ch], have been integrated. Modifications to
    src/system.c enable MMIO read and write operations for these
    peripherals. The minimal device tree source file is also integrated in
    src/devices/minimal.dts.
    
    Default termios control flags are set to ICANON | ECHO | ISIG, allowing
    all keyboard input to be captured by the guestOS.
    
    The CLI parser has been updated to support custom Linux Kernel Images,
    rootfs, and Device Tree Blobs.
    
    The ELF_LOADER has been introduced to support test suites involving
    single ELF files that use the rv32emu built-in syscall. It helps to
    choose the right executable loader and requires differentiation from
    guestOS syscalls.
    
    The csrrw instruction is now branchable since it may overwrite the SATP
    CSR during guestOS process scheduling.
    
    last_pc and is_branch_taken are now updated only when not in a trapped
    state, otherwise might lost the original state of them.
    
    A system make target has been added to simplify running system
    emulation.
    
    Misc changes:
    - Rename 'ARRAYS_SIZE' to 'ARRAY_SIZE' for better readability
    - Move JIT related variables to proper conditional build flag

 Makefile                |  35 +++++++++----
 mk/artifact.mk          |  36 +++++++++++--
 mk/system.mk            |  28 ++++++++++
 src/common.h            |  59 ++++++++++++++++++++-
 src/decode.h            |   2 +-
 src/devices/minimal.dts |  69 +++++++++++++++++++++++++
 src/devices/plic.c      |  91 ++++++++++++++++++++++++++++++++
 src/devices/plic.h      |  41 +++++++++++++++
 src/devices/uart.c      | 151 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/devices/uart.h      |  51 ++++++++++++++++++
 src/emulate.c           | 130 ++++++++++++++++++++++++++++++++++++++++------
 src/feature.h           |   5 ++
 src/io.h                |   1 +
 src/jit.c               |  18 +++----
 src/main.c              |  58 ++++++++++++++++-----
 src/riscv.c             | 317 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++-----------------------------
 src/riscv.h             |  89 ++++++++++++++++++++------------
 src/riscv_private.h     |   4 +-
 src/rv32_template.c     | 271 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---------------------------
 src/system.c            | 295 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---------------------------
 tools/rv_histogram.c    |   4 +-
 21 files changed, 1431 insertions(+), 324 deletions(-)
 create mode 100644 mk/system.mk
 create mode 100644 src/devices/minimal.dts
 create mode 100644 src/devices/plic.c
 create mode 100644 src/devices/plic.h
 create mode 100644 src/devices/uart.c
 create mode 100644 src/devices/uart.h


git bisect start
# status: waiting for both good and bad commits
# bad: [7c1b40c6b21b621470cc8ffe911efafb10112c24] Merge pull request #642 from sysprog21/fix-timidity
git bisect bad 7c1b40c6b21b621470cc8ffe911efafb10112c24
# status: waiting for good commit(s), bad commit known
# good: [4ad4f43ced24eb8a73043e8c3c5fb0ba71b62dbc] Merge pull request #464 from ChinYikMing/fence
git bisect good 4ad4f43ced24eb8a73043e8c3c5fb0ba71b62dbc
# bad: [80658a81e36c3f384f7e9ffcca973df2807a9cea] Merge pull request #549 from otteryc/mac_gsha1
git bisect bad 80658a81e36c3f384f7e9ffcca973df2807a9cea
# good: [6647215c4ef917d486e34b175732a38b7ceb4591] Merge pull request #516 from sysprog21/ci-bump-gnu-toolchain
git bisect good 6647215c4ef917d486e34b175732a38b7ceb4591
# bad: [8de334b62f829bf1077e74471fe525b6868984aa] Fix compiler errors with JIT when Zbb is disabled
git bisect bad 8de334b62f829bf1077e74471fe525b6868984aa
# bad: [79483f8d6d83ecea6459d622b7ab962f28681018] CI: Add Zba, Zbb, Zbc, and Zbs tests to CI pipeline
git bisect bad 79483f8d6d83ecea6459d622b7ab962f28681018
# bad: [04e7396c590b0ace7ffa85ae4618c5d6d63eea9a] Merge pull request #508 from ChinYikMing/feat/bring-up-linux
git bisect bad 04e7396c590b0ace7ffa85ae4618c5d6d63eea9a
# good: [451f8c0a9990e9beb4be8c286c07f67ed1bbbf81] Merge pull request #518 from vacantron/jit/cache
git bisect good 451f8c0a9990e9beb4be8c286c07f67ed1bbbf81
# bad: [27157856eb25260d0c4fbc3cb5c9730eb54546ad] CI: Add Linux booting verification
git bisect bad 27157856eb25260d0c4fbc3cb5c9730eb54546ad
# bad: [e701b40957ac97fac78234d6447a8553a7d3b2c9] Enable to build custom Linux image
git bisect bad e701b40957ac97fac78234d6447a8553a7d3b2c9
# bad: [a6ecb0c4e9bb06c6348d51dfa2bc2aa8a602d2b1] Bring up Linux kernel
git bisect bad a6ecb0c4e9bb06c6348d51dfa2bc2aa8a602d2b1
# first bad commit: [a6ecb0c4e9bb06c6348d51dfa2bc2aa8a602d2b1] Bring up Linux kernel

[visitorckw]

The identified commit is extensive (1,400+ insertions across 21 files), integrating multiple distinct components simultaneously. This complexity makes it impossible to cleanly revert the commit on top of the current tree to isolate the problem. For future development, breaking such large changes into atomic commits would be extremely helpful.