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this issue mainly affects PIE binaries and execution of programs via direct invocation of the dynamic linker binary: depending on kernel behavior, in these cases the initial brk may be placed at at location where it cannot be extended, due to conflicting adjacent maps. when brk fails, mmap is used instead to expand the heap. in order to avoid expensive bookkeeping for managing fragmentation by merging these new heap regions, the minimum size for new heap regions increases exponentially in the number of regions. this limits the number of regions, and thereby the number of fixed fragmentation points, to a quantity which is logarithmic with respect to the size of virtual address space and thus negligible. the exponential growth is tuned so as to avoid expanding the heap by more than approximately 50% of its current total size.
musl libc
musl, pronounced like the word "mussel", is an MIT-licensed
implementation of the standard C library targetting the Linux syscall
API, suitable for use in a wide range of deployment environments. musl
offers efficient static and dynamic linking support, lightweight code
and low runtime overhead, strong fail-safe guarantees under correct
usage, and correctness in the sense of standards conformance and
safety. musl is built on the principle that these goals are best
achieved through simple code that is easy to understand and maintain.
The 1.0 release series for musl features coverage for all interfaces
defined in ISO C99 and POSIX 2008 base, along with a number of
non-standardized interfaces for compatibility with Linux, BSD, and
glibc functionality.
For basic installation instructions, see the included INSTALL file.
Information on full musl-targeted compiler toolchains, system
bootstrapping, and Linux distributions built on musl can be found on
the project website:
http://www.musl-libc.org/