l2k15: guenther@ on hacking libc symbols

Fresh from the l2k15 hackathon, here comes Philip Guenther's (guenther@) report:

Mmmm, fresh burek and other pastries for breakfast, with plums fromthe farmer's market to slurp down while hacking. It was a greattrip...

I spent most of l2k15 banging on libc with Theo. We finally startedexplicitly specifying the exported symbols late last month andmanaged to chop about 200 symbols from the export list before thehackathon. During the hackathon we made further progress on twofronts:

• we stopped exporting another 100 symbols or so by hiding internal APIs and, in some cases, deleting routines or moving them into particular applications. Theo did most of this.
• we stopped permitting overriding of many internal calls in libc. I did most of this.

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