Rich Felker
4ff234f6cb
when loading libraries with dlopen, the caller can request that the library's symbols become part of the global symbol table, or that they only be used for resolving relocations in the loaded library and its dependencies. in the latter case, a subsequent dlopen of the same library can upgrade it to global status. previously, if a library was upgraded from local to global mode, its symbols entered the symbol lookup search order at the point where the library was originally loaded. this means that a new call to dlopen could change the value of a symbol that already had a visible definition, an inconsistency which applications could observe. POSIX is unclear whether this should happen or whether it's permitted to happen, but the resolution of Austin Group issue #982 made it formally unspecified. with this patch, a library whose mode is upgraded from local to global enters the symbol lookup order at the point where it was made global, so that symbol resolution before and after the upgrade are consistent. in order to implement this change, the per-dso global flag is replaced with a separate set of linked-list pointers for participation in the global symbol table. this permits the order of dso objects for symbol resolution to differ from the order used for iteration of all loaded libraries. it also improves performance of find_sym, by avoiding a branch per iteration and skipping, and especially in the case where many non-global libraries have been loaded, by allowing the loop to skip over them entirely. logic for temporarily adding non-global libraries to the symbol table for relocation purposes is also mildly simplified.
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 1.1 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/