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This patch changes the return type of sys::Process::getPageSize to Expected<unsigned> to account for the fact that the underlying syscalls used to obtain the page size may fail (see below). For clients who use the page size as an optimization only this patch adds a new method, getPageSizeEstimate, which calls through to getPageSize but discards any error returned and substitues a "reasonable" page size estimate estimate instead. All existing LLVM clients are updated to call getPageSizeEstimate rather than getPageSize. On Unix, sys::Process::getPageSize is implemented in terms of getpagesize or sysconf, depending on which macros are set. The sysconf call is documented to return -1 on failure. On Darwin getpagesize is implemented in terms of sysconf and may also fail (though the manpage documentation does not mention this). These failures have been observed in practice when highly restrictive sandbox permissions have been applied. Without this patch, the result is that getPageSize returns -1, which wreaks havoc on any subsequent code that was assuming a sane page size value. <rdar://problem/41654857> Reviewers: dblaikie, echristo Subscribers: kristina, llvm-commits Tags: #llvm Differential Revision: https://reviews.llvm.org/D59107 llvm-svn: 360221
llvm/lib/Support/Unix README =========================== This directory provides implementations of the lib/System classes that are common to two or more variants of UNIX. For example, the directory structure underneath this directory could look like this: Unix - only code that is truly generic to all UNIX platforms Posix - code that is specific to Posix variants of UNIX SUS - code that is specific to the Single Unix Specification SysV - code that is specific to System V variants of UNIX As a rule, only those directories actually needing to be created should be created. Also, further subdirectories could be created to reflect versions of the various standards. For example, under SUS there could be v1, v2, and v3 subdirectories to reflect the three major versions of SUS.