Fix LinuxUserland::read_maps to handle large /proc/self/maps output - #1407
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read_maps() read /proc/self/maps into a fixed 8 KiB stack buffer and asserted the read fit, panicking with "buffer too small" once the process had enough mappings to exceed that size. This was hit in CI as a timing-dependent race: the broker starting worker threads while read_maps() was capturing the process's mappings could push the file past 8 KiB. Replace the fixed-size read with an EOF-driven loop into a growable buffer, backing off gracefully (keeping whatever was read so far) if growing the buffer fails, consistent with this function's existing best-effort contract (it already returns nothing if the file can't be opened, and mappings created during/after the read are still not guaranteed to be captured). Parsing now works directly off the raw bytes instead of requiring the whole file to be valid UTF-8, since a mapped file's pathname field isn't guaranteed to be one. Adds a regression test that creates thousands of small mappings to push /proc/self/maps past the old 8 KiB limit and calls read_maps() directly, verifying it no longer panics. Fixes microsoft#1328
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Thanks for the contribution! However, I'm working on refactoring/redesigning the memory management interfaces and this PR would become unnecessary then. |
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As described in [issue #1328](#1328),
read_maps()could panic when/proc/self/mapsexceeded its fixed 8 KiB buffer, sometimes triggered by worker threads starting during the read.Read into a growable buffer until EOF, retaining partial data if allocation fails. Parse the raw bytes so non-UTF-8 pathnames do not prevent parsing. Add a regression test with thousands of mappings that exceed the old limit.