o 文件都放在 /tmp 中；具体来说，SCons 会在 /tmp/username 中创建一个目录树，并将输出文件放到这个目录中，从而避免在非绝对必要的情况下修改构建树。

The .o files are placed in /tmp; specifically, SCons builds a directory tree in /tmp/username in which it stores output files so as to avoid altering the build tree more than absolutely necessary.

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