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first calls mmap() with the arguments PROT_NONE and MAP_ANON to reserve a single, contiguous range of virtual addresses for the entire shared library. Later, rtld calls mmap() with the the shared library's file descriptor and the argument MAP_FIXED to place the text and data sections within the reserved range. The rationale for mapping shared libraries in this way is explained in the commit message for Revision 190885. However, this approach does have an unintended, negative consequence. Since the first call to mmap() specifies MAP_ANON and not the shared library's file descriptor, the kernel has no idea what alignment the vm object backing the file prefers. As a result, the reserved range's alignment is unlikely to be the same as the vm object's, and so mapping with superpages becomes impossible. To address this problem, this revision adds the argument MAP_ALIGNED_SUPER to the first call to mmap() if the text section is larger than the smallest superpage size. To determine if the text section is larger than the smallest superpage size, rtld must always fetch the page size information. As a result, the private code for fetching the base page size in rtld's builtin malloc is redundant. Eliminate it. Requested by: kib Tested by: zbb (on arm) Reviewed by: kib (an earlier version) Discussed with: jhb
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