add git bisect

_posts/2024-03-07-git-bisect.md

@@ -0,0 +1,74 @@
+---
+layout: post
+title: Git Bisect定位问题
+author: "Fei Wu"
+header-mask: 0.4
+tags:
+  - git-bisect
+  - RISC-V
+  - Debug
+---
+
+# 复现问题
+
+发现rva22s64出现hang，复现脚本
+
+```
+$QEMU -machine virt -nographic -m 2G -smp 2 \
+    -cpu rva22s64 \
+    -bios $d/fw_jump.elf \
+    -kernel $d/kernel-latest &> log &
+```
+
+只要看到最后停在哪里就可以知道有没有问题
+
+# bisect脚本
+
+稍微改造一下上面的测试用例
+
+```
+$ cat check-qemu
+#!/bin/bash
+
+QEMU_SRC=~/qemu
+QEMU=$QEMU_SRC/install/bin/qemu-system-riscv64
+
+pushd $QEMU_SRC
+make -j 64 install
+popd
+
+$d=~/wufei/rvsp
+tm=$(date +%s)
+log=$d/log-$tm
+
+$QEMU -machine virt -nographic -m 2G -smp 2 \
+    -cpu rva22s64 \
+    -bios $d/fw_jump.elf \
+    -kernel $d/kernel-latest &> log &
+
+pid=$!
+sleep 5
+kill -9 $pid
+
+if tail -1 $log | grep MEDELEG; then
+    exit 1
+else
+    exit 0
+fi
+```
+
+# 执行bisect
+
+```
+$ git bisect start master dfa3c4c57e
+$ git bisect run check-qemu
+
+d06f28db60c536b9d7f159adedca397979f6e5ca is the first bad commit
+commit d06f28db60c536b9d7f159adedca397979f6e5ca
+Author: Daniel Henrique Barboza <[email protected]>
+Date: Fri Jan 5 20:05:33 2024 -0300
+
+    target/riscv: move 'mmu' to riscv_cpu_properties[]
+```
+
+bisect特别适合这类任务，总共不到一小时内定位问题，直接上去调试代码肯定需要更多时间。