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2021-09-23add qsort_r and make qsort a wrapper around itÉrico Nogueira1-0/+1
we make qsort a wrapper by providing a wrapper_cmp function that uses the extra argument as a function pointer. should be optimized to a tail call on most architectures, as long as it's built with -fomit-frame-pointer, so the performance impact should be minimal. to keep the git history clean, for now qsort_r is implemented in qsort.c and qsort is implemented in qsort_nr.c. qsort.c also received a few trivial cleanups, including replacing (*cmp)() calls with cmp(). qsort_nr.c contains only wrapper_cmp and qsort as a qsort_r wrapper itself.
2020-11-11give libc access to its own malloc even if public malloc is interposedRich Felker1-0/+6
allowing the application to replace malloc (since commit c9f415d7ea2dace5bf77f6518b6afc36bb7a5732) has brought multiple headaches where it's used from various critical sections in libc components. for example: - the thread-local message buffers allocated for dlerror can't be freed at thread exit time because application code would then run in the context of a non-existant thread. this was handled in commit aa5a9d15e09851f7b4a1668e9dbde0f6234abada by queuing them for free later. - the dynamic linker has to be careful not to pass memory allocated at early startup time (necessarily using its own malloc) to realloc or free after redoing relocations with the application and all libraries present. bugs in this area were fixed several times, at least in commits 0c5c8f5da6e36fe4ab704bee0cd981837859e23f and 2f1f51ae7b2d78247568e7fdb8462f3c19e469a4 and possibly others. - by calling the allocator from contexts where libc-internal locks are held, we impose undocumented requirements on alternate malloc implementations not to call into any libc function that might attempt to take these locks; if they do, deadlock results. - work to make fork of a multithreaded parent give the child an unrestricted execution environment is blocked by lock order issues as long as the application-provided allocator can be called with libc-internal locks held. these problems are all fixed by giving libc internals access to the original, non-replaced allocator, for use where needed. it can't be used everywhere, as some interfaces like str[n]dup, open_[w]memstream, getline/getdelim, etc. are required to provide the called memory obtained as if by (the public) malloc. and there are a number of libc interfaces that are "pure library" code, not part of some internal singleton, and where using the application's choice of malloc implementation is preferable -- things like glob, regex, etc. one might expect there to be significant cost to static-linked programs, pulling in two malloc implementations, one of them mostly-unused, if malloc is replaced. however, in almost all of the places where malloc is used internally, care has been taken already not to pull in realloc/free (i.e. to link with just the bump allocator). this size optimization carries over automatically. the newly-exposed internal allocator functions are obtained by renaming the actual definitions, then adding new wrappers around them with the public names. technically __libc_realloc and __libc_free could be aliases rather than needing a layer of wrapper, but this would almost surely break certain instrumentation (valgrind) and the size and performance difference is negligible. __libc_calloc needs to be handled specially since calloc is designed to work with either the internal or the replaced malloc. as a bonus, this change also eliminates the longstanding ugly dependency of the static bump allocator on order of object files in libc.a, by making it so there's only one definition of the malloc function and having it in the same source file as the bump allocator.
2018-09-12use wrapper headers to hide most namespaced/internally-public symbolsRich Felker1-5/+5
not all prefixed symbols can be made hidden. some are part of ABI-compat (e.g. __nl_langinfo_l) and others are ABI as a consequence of the way copy relocations for weak aliases work in ELF shared libraries. most, however, can be made hidden. with this commit, there should be no remaining unintentionally visible symbols exported from libc.so.
2018-09-12declare __env_rm_add in wrapper stdlib.hRich Felker1-0/+1
this is perhaps not the ideal place, but no better alternatives stand out.
2018-09-12overhaul internally-public declarations using wrapper headersRich Felker1-0/+11
commits leading up to this one have moved the vast majority of libc-internal interface declarations to appropriate internal headers, allowing them to be type-checked and setting the stage to limit their visibility. the ones that have not yet been moved are mostly namespace-protected aliases for standard/public interfaces, which exist to facilitate implementing plain C functions in terms of POSIX functionality, or C or POSIX functionality in terms of extensions that are not standardized. some don't quite fit this description, but are "internally public" interfacs between subsystems of libc. rather than create a number of newly-named headers to declare these functions, and having to add explicit include directives for them to every source file where they're needed, I have introduced a method of wrapping the corresponding public headers. parallel to the public headers in $(srcdir)/include, we now have wrappers in $(srcdir)/src/include that come earlier in the include path order. they include the public header they're wrapping, then add declarations for namespace-protected versions of the same interfaces and any "internally public" interfaces for the subsystem they correspond to. along these lines, the wrapper for features.h is now responsible for the definition of the hidden, weak, and weak_alias macros. this means source files will no longer need to include any special headers to access these features. over time, it is my expectation that the scope of what is "internally public" will expand, reducing the number of source files which need to include *_impl.h and related headers down to those which are actually implementing the corresponding subsystems, not just using them.