this style is preferred because it allows the code to be compile-checked even on archs where it is not used.
mips has its own mechanisms for DT_DEBUG because it makes _DYNAMIC read-only, and the original mechanism, DT_MIPS_RLD_MAP, was PIE-incompatible. DT_MIPS_RLD_MAP_REL was added to remedy this, but we never implemented support for it. add it now using the same idioms for mips-specific ldso logic.
this resolves DT_RELR relocations in non-ldso, dynamic-linked objects.
this is in preparation for improving behavior of malloc interposition.
a new weak predicate function replacable by the malloc implementation, __malloc_allzerop, is introduced. by default it's always false; the default version will be used when static linking if the bump allocator was used (in which case performance doesn't matter) or if malloc was replaced by the application. only if the real internal malloc is linked (always the case with dynamic linking) does the real version get used. if malloc was replaced dynamically, as indicated by __malloc_replaced, the predicate function is ignored and conditional-memset is always performed.
this eliminates consumers of malloc_impl.h outside of the malloc implementation.
this interface contract is entirely internal to dynlink.c.
R_PPC_UADDR32 (R_PPC64_UADDR64) has the same meaning as R_PPC_ADDR32 (R_PPC64_ADDR64), except that its address need not be aligned. For powerpc64, BFD ld(1) will automatically convert between ADDR<->UADDR relocations when the address is/isn't at its native alignment. This will happen if, for example, there is a pointer in a packed struct. gold and lld do not currently generate R_PPC64_UADDR64, but pass through misaligned R_PPC64_ADDR64 relocations from object files, possibly relaxing them to misaligned R_PPC64_RELATIVE. In both cases (relaxed or not) this violates the PSABI, which defines the relevant field type as "a 64-bit field occupying 8 bytes, the alignment of which is 8 bytes unless otherwise specified." All three linkers violate the PSABI on 32-bit powerpc, where the only difference is that the field is 32 bits wide, aligned to 4 bytes. Currently musl fails to load executables linked by BFD ld containing R_PPC64_UADDR64, with the error "unsupported relocation type 43". This change provides compatibility with BFD ld on powerpc64, and any static linker on either architecture that starts following the PSABI more closely.
_Noreturn is a C11 construct, and may only be used at the site of a function definition.
libc.h was intended to be a header for access to global libc state and related interfaces, but ended up included all over the place because it was the way to get the weak_alias macro. most of the inclusions removed here are places where weak_alias was needed. a few were recently introduced for hidden. some go all the way back to when libc.h defined CANCELPT_BEGIN and _END, and all (wrongly implemented) cancellation points had to include it. remaining spurious users are mostly callers of the LOCK/UNLOCK macros and files that use the LFS64 macro to define the awful *64 aliases. in a few places, new inclusion of libc.h is added because several internal headers no longer implicitly include libc.h. declarations for __lockfile and __unlockfile are moved from libc.h to stdio_impl.h so that the latter does not need libc.h. putting them in libc.h made no sense at all, since the macros in stdio_impl.h are needed to use them correctly anyway.