[CommandLine][Linux] Don't read argv from /proc/self/cmdline (take 2). #71781
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This reverts the reversion of swiftlang#71611. rdar://117963394
In `/proc/self/maps`, the stack isn't necessarily a single range, even immediately after process start-up. Apparently sometimes it's possible for the kernel to allocate extra ranges below the first one, and these show up separately in `/proc/self/maps`. The upshot was that we were finding that `environ` didn't point into the stack range we found, and then returning no arguments as a result. The fix is to merge contiguous ranges after the first stack range we find in `/proc/self/maps`. rdar://117963394
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@swift-ci Please smoke test |
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@swift-ci Please test Linux platform |
mikeash
approved these changes
Feb 21, 2024
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Original PR was #71611. This is a replacement for that, with a bug fix. |
This was referenced Feb 26, 2024
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Instead of reading from
/proc/self/cmdline, take advantage of the fact that the initial stack layout is ABI specified, and that we already have a pointer into it (environ). This lets us walk up the stack until we findargc, at which point we also know whereargvis.We do this from a static initializer because a
setenv()orputenv()can changeenviron(if you add a new environment variable), and it's even permissible to just outright changeenvironyourself too. It seems reasonable to suggest to people that they shouldn't be doing those things from a static initializer, and as long as they don't, they won't run before we've had a chance to findargv.Just in case someone does do this, we also check that
environpoints into the stack. If it doesn't, they won't get any arguments, so if that happens, that's a clue that they're messing withenvirontoo early.This works around a problem (#69658) with Docker Desktop 4.25.0 and Rosetta, wherein we end up with an extra argument visible in
/proc/self/cmdline, and also avoids allocating memory for the command line arguments.rdar://117963394