anecdotes:not_expected_to_understand_this
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| anecdotes:not_expected_to_understand_this [2016/01/12 10:31] – created wkt | anecdotes:not_expected_to_understand_this [2016/01/12 10:32] – wkt | ||
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| ===== /* You are not expected to understand this */ ===== | ===== /* You are not expected to understand this */ ===== | ||
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| + | (taken from Dennis Ritchie' | ||
| Every now and then on Usenet or elsewhere I run across a reference to a certain comment in the source code of the Sixth Edition Unix operating system. | Every now and then on Usenet or elsewhere I run across a reference to a certain comment in the source code of the Sixth Edition Unix operating system. | ||
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| It's often quoted as a slur on the quantity or quality of the comments in the Bell Labs research releases of Unix. Not an unfair observation in general, I fear, but in this case unjustified. The actual code and other commentary surrounding it were precisely this: | It's often quoted as a slur on the quantity or quality of the comments in the Bell Labs research releases of Unix. Not an unfair observation in general, I fear, but in this case unjustified. The actual code and other commentary surrounding it were precisely this: | ||
| - | < | + | < |
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| * Switch to stack of the new process and set up | * Switch to stack of the new process and set up | ||
| * his segmentation registers. | * his segmentation registers. | ||
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| */ | */ | ||
| return(1); | return(1); | ||
| - | '' | ||
| </ | </ | ||
| - | So we tried to explain what was going on. "You are not expected to understand this" was intended as a remark in the spirit of "This won't be on the exam," rather than as an impudent challenge. | + | |
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| The real problem is that we didn't understand what was going on either. The savu/retu mechanism for doing process exchange was fundamentally broken because it depended on switching to a previous stack frame and executing function return code in a different procedure from the one that saved the earlier state. This worked on the PDP-11 because its compiler always used the same context-save mechanism; with the Interdata compiler, the procedure return code differed depending on which registers were saved. | The real problem is that we didn't understand what was going on either. The savu/retu mechanism for doing process exchange was fundamentally broken because it depended on switching to a previous stack frame and executing function return code in a different procedure from the one that saved the earlier state. This worked on the PDP-11 because its compiler always used the same context-save mechanism; with the Interdata compiler, the procedure return code differed depending on which registers were saved. | ||
anecdotes/not_expected_to_understand_this.txt · Last modified: 2022/07/08 09:22 by 192.99.0.24