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5 daysfix regression in dl_iterate_phdr reporting of modules with no TLSHEADmasterRich Felker-1/+2
__tls_get_addr should not be called with an invalid TLS module id of 0. in practice it probably "works", returning the DTV length as if it were a pointer, and the callback should probably not inspect dlpi_tls_data in this case, but it's likely that some real-world callbacks use a check on dlpi_tls_data being non-null, rather than on dlpi_tls_modid being nonzero, to conclude that the module has TLS.
2021-03-26fix dl_iterate_phdr dlpi_tls_data reporting to match specRich Felker-1/+1
dl_iterate_phdr was wrongly reporting the address of the DSO's PT_TLS image rather than the calling thread's instance of the TLS. the man page, which is essentially normative for a nonstandard function of this sort, clearly specifies the latter. it does not clarify where exactly within/relative-to the image the pointer should point, but the reasonable thing to do is match the ABI's DTP offset, and this seems to be what other implementations do.
2021-03-05don't fail to map library/executable with zero-length segment mapsRich Felker-0/+1
reportedly the GNU linker can emit such segments, causing spurious failure to load due to mmap with a length of zero producing EINVAL. no action is required for such a load map (it's effectively a nop in the program headers table) so just treat it as always successful.
2020-11-11lift child restrictions after multi-threaded forkRich Felker-0/+19
as the outcome of Austin Group tracker issue #62, future editions of POSIX have dropped the requirement that fork be AS-safe. this allows but does not require implementations to synchronize fork with internal locks and give forked children of multithreaded parents a partly or fully unrestricted execution environment where they can continue to use the standard library (per POSIX, they can only portably use AS-safe functions). up until recently, taking this allowance did not seem desirable. however, commit 8ed2bd8bfcb4ea6448afb55a941f4b5b2b0398c0 exposed the extent to which applications and libraries are depending on the ability to use malloc and other non-AS-safe interfaces in MT-forked children, by converting latent very-low-probability catastrophic state corruption into predictable deadlock. dealing with the fallout has been a huge burden for users/distros. while it looks like most of the non-portable usage in applications could be fixed given sufficient effort, at least some of it seems to occur in language runtimes which are exposing the ability to run unrestricted code in the child as part of the contract with the programmer. any attempt at fixing such contracts is not just a technical problem but a social one, and is probably not tractable. this patch extends the fork function to take locks for all libc singletons in the parent, and release or reset those locks in the child, so that when the underlying fork operation takes place, the state protected by these locks is consistent and ready for the child to use. locking is skipped in the case where the parent is single-threaded so as not to interfere with legacy AS-safety property of fork in single-threaded programs. lock order is mostly arbitrary, but the malloc locks (including bump allocator in case it's used) must be taken after the locks on any subsystems that might use malloc, and non-AS-safe locks cannot be taken while the thread list lock is held, imposing a requirement that it be taken last.
2020-11-11convert malloc use under libc-internal locks to use internal allocatorRich Felker-0/+5
this change lifts undocumented restrictions on calls by replacement mallocs to libc functions that might take these locks, and sets the stage for lifting restrictions on the child execution environment after multithreaded fork. care is taken to #define macros to replace all four functions (malloc, calloc, realloc, free) even if not all of them will be used, using an undefined symbol name for the ones intended not to be used so that any inadvertent future use will be caught at compile time rather than directed to the wrong implementation.
2020-11-11drop use of getdelim/stdio in dynamic linkerRich Felker-5/+22
the only place stdio was used here was for reading the ldso path file, taking advantage of getdelim to automatically allocate and resize the buffer. the motivation for use here was that, with shared libraries, stdio is already available anyway and free to use. this has long been a nuisance to users because getdelim's use of realloc here triggered a valgrind bug, but removing it doesn't really fix that; on some archs even calling the valgrind-interposed malloc at this point will crash. the actual motivation for this change is moving towards getting rid of use of application-provided malloc in parts of libc where it would be called with libc-internal locks held, leading to the possibility of deadlock if the malloc implementation doesn't follow unwritten rules about which libc functions are safe for it to call. since getdelim is required to produce a pointer as if by malloc (i.e. that can be passed to reallor or free), it necessarily must use the public malloc. instead of performing a realloc loop as the path file is read, first query its size with fstat and allocate only once. this produces slightly different truncation behavior when racing with writes to a file, but neither behavior is or could be made safe anyway; on a live system, ldso path files should be replaced by atomic rename only. the change should also reduce memory waste.
2020-10-27ldso: notify the debugger when we're doing a dlopenrcombs-2/+6
Otherwise lldb doesn't notice the new library and stack traces containing it get cut off unhelpfully.
2020-10-14ldso: use pthread_t rather than kernel tid to track ctor visitorRich Felker-3/+3
commit 188759bbee057aa94db2bbb7cf7f5855f3b9ab53 documented the intent to allow recursive dlopen based on tracking ctor_visitor, but used a kernel tid rather than the pthread_t to identify the caller. as a result, it would not behave as intended under fork by a ctor, where the child tid would not match.
2020-10-14fix stale lock when allocation of ctor queue fails during dlopenRich Felker-1/+2
queue_ctors should not be called with the init_fini_lock held, since it may longjmp out on allocation failure. this introduces a minor TOCTOU race with p->constructed, but one already exists further down anyway, and by design it's okay to run through the queue more than once anyway. the only reason we bother to check p->constructed at all is to avoid spurious failure of dlopen when the library is already fully loaded and constructed.
2020-08-27remove redundant pthread struct members repeated for layout purposesRich Felker-1/+1
dtv_copy, canary2, and canary_at_end existed solely to match multiple ABI and asm-accessed layouts simultaneously. now that pthread_arch.h can be included before struct __pthread is defined, the struct layout can depend on macros defined by pthread_arch.h.
2020-06-10have ldso track replacement of aligned_allocRich Felker-0/+2
this is in preparation for improving behavior of malloc interposition.
2020-06-02move declaration of interfaces between malloc and ldso to dynlink.hRich Felker-1/+0
this eliminates consumers of malloc_impl.h outside of the malloc implementation.
2020-03-20ldso: remove redundant switch case for REL_NONEFangrui Song-2/+0
as a result of commit b6a6cd703ffefa6352249fb01f4da28d85d17306, the REL_NONE case is now redundant.
2020-01-15fix incorrect __hwcap seen in dynamic-linked __set_thread_areaRich Felker-1/+1
the bug fixed in commit b82cd6c78d812d38c31febba5a9e57dbaa7919c4 was mostly masked on arm because __hwcap was zero at the point of the call from the dynamic linker to __set_thread_area, causing the access to libc.auxv to be skipped and kuser_helper versions of TLS access and atomics to be used instead of the armv6 or v7 versions. however, on kernels with kuser_helper removed for hardening it would crash. since __set_thread_area potentially uses __hwcap, it must be initialized before the function is called. move the AT_HWCAP lookup from stage 3 to stage 2b.
2020-01-01fix fdpic regression in dynamic linker with overly smart compilersRich Felker-2/+8
at least gcc 9 broke execution of DT_INIT/DT_FINI for fdpic archs (presently only sh) by recognizing that the stores to the compound-literal function descriptor constructed to call them were dead stores. there's no way to make a "may_alias function", so instead launder the descriptor through an asm-statement barrier. in practice just making the compound literal volatile seemed to have worked too, but this should be less of a hack and more accurately convey the semantics of what transformations are not valid.
2019-12-31fix crashing ldso on archs where __set_thread_area examines auxvRich Felker-13/+13
commit 1c84c99913bf1cd47b866ed31e665848a0da84a2 moved the call to __init_tp above the initialization of libc.auxv, inadvertently breaking archs where __set_thread_area examines auxv for the sake of determining the TLS/atomic model needed at runtime. this broke armv6 and sh2.
2019-12-31move stage3_func typedef out of shared internal dynlink.h headerRich Felker-0/+2
this interface contract is entirely internal to dynlink.c.
2019-11-02add time64 redirect for, and redirecting implementation of, dlsymRich Felker-0/+27
if symbols are being redirected to provide the new time64 ABI, dlsym must perform matching redirections; otherwise, it would poke a hole in the magic and return pointers to functions that are not safe to call from a caller using time64 types. rather than duplicating a table of redirections, use the time64 symbols present in libc's symbol table to derive the decision for whether a particular symbol needs to be redirected.
2019-08-13fix regression whereby main thread didn't get TLS relocationsRich Felker-7/+13
commit ffab43602b5900c86b7040abdda8ccf6cdec95f5 broke this by moving relocations after not only the allocation of storage for the main thread's static TLS, but after the copying of the TLS image. thus, relocation results were not reflected in the main thread's copy. this could be fixed by calling __reset_tls after relocations, but instead split the allocation and installation before/after relocations so that there's not a redundant copy. due to commit 71af5309874269bcc9e4b84ea716fab33d888c1d, updating of static_tls_cnt needs to be kept with allocation of static TLS, before relocations, rather than after installation.
2019-08-12make relocation time symbol lookup and dlsym consistentSzabolcs Nagy-53/+31
Using common code path for all symbol lookups fixes three dlsym issues: - st_shndx of STT_TLS symbols were not checked and thus an undefined tls symbol reference could be incorrectly treated as a definition (the sysv hash lookup returns undefined symbols, gnu does not, so should be rare in practice). - symbol binding was not checked so a hidden symbol may be returned (in principle STB_LOCAL symbols may appear in the dynamic symbol table for hidden symbols, but linkers most likely don't produce it). - mips specific behaviour was not applied (ARCH_SYM_REJECT_UND) so undefined symbols may be returned on mips. always_inline is used to avoid relocation performance regression, the code generation for find_sym should not be affected.
2019-08-12ldso: correct condition for local symbol handling in do_relocsRich Felker-1/+1
commit 7a9669e977e5f750cf72ccbd2614f8b72ce02c4c added use of the symbol reference as the definition, in place of performing a lookup, for STT_SECTION symbol references that were first found used in FDPIC. such references may happen in certain other cases, such as local-dynamic TLS and with relocation types that require a symbol but that are being used for non-symbolic purposes, like the powerpc unaligned address relocations. in all such cases I'm aware of, the symbol referenced is a section symbol (STT_SECTION); however, the important semantic property is not its being a section, but rather its binding local (STB_LOCAL). check the latter instead of the former for greater generality and semantic correctness.
2019-08-11add support for powerpc/powerpc64 unaligned relocationsSamuel Holland-0/+3
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.
2019-08-11ldso: remove redundant runtime checks in static TLS logicRich Felker-2/+2
as a result of commit ffab43602b5900c86b7040abdda8ccf6cdec95f5, static_tls_cnt is now valid during relocations at program startup, so it's no longer necessary to condition the check against static_tls_cnt on this being a runtime (dlopen) relocation.
2019-08-11ldso: fix calloc misuse allocating initial tlsRich Felker-5/+7
this is analogous to commit 2f1f51ae7b2d78247568e7fdb8462f3c19e469a4, and should have been caught at the same time since it was right next to the code moved in that commit. between final stage 3 reloc_all and the jump to the main program's entry point, it is not valid to call any functions which may be interposed by the application; doing so results in execution of application code before ctors have run, and on fdpic archs, before the main program's fdpic self-fixups have taken place, which will produce runaway wrong execution.
2019-07-06fix inadvertent use of uninitialized variable in dladdrRich Felker-1/+1
commit c8b49b2fbc7faa8bf065220f11963d76c8a2eb93 introduced code that checked bestsym to determine whether a matching symbol was found, but bestsym is uninitialized if not. instead use best, consistent with use in the rest of the function. simplified from bug report and patch by Cheng Liu.
2019-06-25remove unnecessary and problematic _Noreturn from crt/ldso startupRich Felker-2/+2
after commit a48ccc159a5fa061a18419296100ee48a1cd6cc9 removed the use of _Noreturn on the stage3_func type (which only worked due to it being defined to the "GNU C" attribute in C99 mode), GCC could no longer assume that the ends of __dls2 and __dls2b are unreachable, and produced a warning that a function marked _Noreturn returns. also, since commit 4390383b32250a941ec616e8bff6f568a801b1c0, the _Noreturn declaration for __libc_start_main in crt1/rcrt1 has been not only inconsistent with the definition, but wrong. formally, __libc_start_main does return, via a (hopefully) tail call to a helper function after the barrier. incorrect usage of _Noreturn in the declaration was probably formal UB. the _Noreturn specifiers were not useful in any of these places, so remove them all. now, the only remaining usage of _Noreturn is in public interfaces where _Noreturn is part of their contract.
2019-05-16fix tls offsets when p_vaddr%p_align != 0 on TLS_ABOVE_TP targetsSzabolcs Nagy-3/+4
currently the bfd linker does not seem to create tls segments where p_vaddr%p_align != 0, but this is valid in ELF and then the runtime computed tls offset must satisfy offset%p_align == (base+p_vaddr)%p_align and in case of local exec tls (main executable) the smallest such offset must be used (otherwise it is incompatible with the offset computed by the static linker). the !TLS_ABOVE_TP case is handled correctly (the offset is negative then in the formula). the ldso code for TLS_ABOVE_TP is changed so the static tls offset of each module satisfies the formula.
2019-05-16fix static tls offsets of shared libs on TLS_ABOVE_TP targetsSzabolcs Nagy-4/+2
tls_offset should always point to the end of the allocated static tls area, but this was not handled correctly on "tls variant 1" targets in the dynamic linker: after application tls was allocated, tls_offset was aligned up, potentially wasting tls space. (alignment may be needed at the begining of the tls area, not at the end, but that will be fixed separately as it is unlikely to affect real binaries.) when static tls was allocated for a shared library, tls_offset was only updated with the size of the tls segment which does not include alignment gaps, which can easily happen if the tls size update for one library leaves tls_offset misaligned for the next one. this can cause oob access in __copy_tls or arbitrary breakage at tls access. (the issue was observed on aarch64 with rust binaries)
2019-05-12remove unused struct dso members from dynlink.cFangrui Song-1/+0
maintainer's note: commit 9d44b6460ab603487dab4d916342d9ba4467e6b9 removed their use.
2019-04-10overhaul i386 syscall mechanism not to depend on external asm sourceRich Felker-0/+3
this is the first part of a series of patches intended to make __syscall fully self-contained in the object file produced using syscall.h, which will make it possible for crt1 code to perform syscalls. the (confusingly named) i386 __vsyscall mechanism, which this commit removes, was introduced before the presence of a valid thread pointer was mandatory; back then the thread pointer was setup lazily only if threads were used. the intent was to be able to perform syscalls using the kernel's fast entry point in the VDSO, which can use the sysenter (Intel) or syscall (AMD) instruction instead of int $128, but without inlining an access to the __syscall global at the point of each syscall, which would incur a significant size cost from PIC setup everywhere. the mechanism also shuffled registers/calling convention around to avoid spills of call-saved registers, and to avoid allocating ebx or ebp via asm constraints, since there are plenty of broken-but-supported compiler versions which are incapable of allocating ebx with -fPIC or ebp with -fno-omit-frame-pointer. the new mechanism preserves the properties of avoiding spills and avoiding allocation of ebx/ebp in constraints, but does it inline, using some fairly simple register shuffling, and uses a field of the thread structure rather than global data for the vdso-provided syscall code address. for now, the external __syscall function is refactored not to use the old __vsyscall so it can be kept, but the intent is to remove it too.
2019-04-06fix the use of syscall result in dl_mmapIlya Matveychikov-1/+1
2019-04-02delete a redundant if in dynamic linker ctor execution loopRay-1/+0
2019-03-10fix invalid-/double-/use-after-free in new dlopen ctor executionRich Felker-1/+2
this affected the error path where dlopen successfully found and loaded the requested dso and all its dependencies, but failed to resolve one or more relocations, causing the operation to fail after storage for the ctor queue was allocated. commit 188759bbee057aa94db2bbb7cf7f5855f3b9ab53 wrongly put the free for the ctor_queue array in the error path inside a loop over each loaded dso that needed to be backed-out, rather than just doing it once. in addition, the exit path also observed the ctor_queue pointer still being nonzero, and would attempt to call ctors on the backed-out dsos unless the double-free crashed the process first.
2019-03-03avoid malloc of ctor queue for programs with no external depsRich Felker-2/+9
together with the previous two commits, this completes restoration of the property that dynamic-linked apps with no external deps and no tls have no failure paths before entry.
2019-03-03avoid malloc of deps arrays for ldso and vdsoRich Felker-0/+3
neither has or can have any dependencies, but since commit 403555690775f7c8806372644f543518e6664e3b, gratuitous zero-length deps arrays were being allocated for them. use a dummy array instead.
2019-03-03avoid malloc of deps array for programs with no external depsRich Felker-3/+10
traditionally, we've provided a guarantee that dynamic-linked applications with no external dependencies (nothing but libc) and no thread-local storage have no failure paths before the entry point. normally, thanks to reclaim_gaps, such a malloc will not require a syscall anyway, but if segment alignment is unlucky, it might. use a builtin array for this common special case.
2019-03-03fix malloc misuse for startup ctor queue, breakage on fdpic archsRich Felker-5/+9
in the case where malloc is being replaced, it's not valid to call malloc between final relocations and main app's crt1 entry point; on fdpic archs the main app's entry point will not yet have performed the self-fixups necessary to call its code. to fix, reorder queue_ctors before final relocations. an alternative solution would be doing the allocation from __libc_start_init, after the entry point but before any ctors run. this is less desirable, since it would leave a call to malloc that might be provided by the application happening at startup when doing so can be easily avoided.
2019-03-03synchronize shared library dtor exec against concurrent loads/ctorsRich Felker-1/+17
previously, going way back, there was simply no synchronization here. a call to exit concurrent with ctor execution from dlopen could cause a dtor to execute concurrently with its corresponding ctor, or could cause dtors for newly-constructed libraries to be skipped. introduce a shutting_down state that blocks further ctor execution, producing the quiescence the dtor execution loop needs to ensure any kind of consistency, and that blocks further calls to dlopen so that a call into dlopen from a dtor cannot deadlock. better approaches to some of this may be possible, but the changes here at least make things safe.
2019-03-03overhaul shared library ctor execution for dependency order, concurrencyRich Felker-17/+101
previously, shared library constructors at program start and dlopen time were executed in reverse load order. some libraries, however, rely on a depth-first dependency order, which most other dynamic linker implementations provide. this is a much more reasonable, less arbitrary order, and it turns out to have much better properties with regard to how slow-running ctors affect multi-threaded programs, and how recursive dlopen behaves. this commit builds on previous work tracking direct dependencies of each dso (commit 403555690775f7c8806372644f543518e6664e3b), and performs a topological sort on the dependency graph at load time while the main ldso lock is held and before success is committed, producing a queue of constructors needed by the newly-loaded dso (or main application). in the case of circular dependencies, the dependency chain is simply broken at points where it becomes circular. when the ctor queue is run, the init_fini_lock is held only for iteration purposes; it's released during execution of each ctor, so that arbitrarily-long-running application code no longer runs with a lock held in the caller. this prevents a dlopen with slow ctors in one thread from arbitrarily delaying other threads that call dlopen. fully-independent ctors can run concurrently; when multiple threads call dlopen with a shared dependency, one will end up executing the ctor while the other waits on a condvar for it to finish. another corner case improved by these changes is recursive dlopen (call from a ctor). previously, recursive calls to dlopen could cause a ctor for a library to be executed before the ctor for its dependency, even when there was no relation between the calling library and the library it was loading, simply due to the naive reverse-load-order traversal. now, we can guarantee that recursive dlopen in non-circular-dependency usage preserves the desired ctor execution order properties, and that even in circular usage, at worst the libraries whose ctors call dlopen will fail to have completed construction when ctors that depend on them run. init_fini_lock is changed to a normal, non-recursive mutex, since it is no longer held while calling back into application code.
2019-03-02record preloaded libraries as direct pseudo-dependencies of main appRich Felker-4/+11
this makes calling dlsym on the main app more consistent with the global symbol table (load order), and is a prerequisite for dependency-order ctor execution to work correctly with LD_PRELOAD.
2019-03-02fix unsafety of new ldso dep tracking in presence of malloc replacementRich Felker-1/+13
commit 403555690775f7c8806372644f543518e6664e3b introduced runtime realloc of an array that may have been allocated before symbols were resolved outside of libc, which is invalid if the allocator has been replaced. track this condition and manually copy if needed.
2019-02-27fix and overhaul dlsym depedency order, always record direct depsRich Felker-34/+79
dlsym with an explicit handle is specified to use "dependency order", a breadth-first search rooted at the argument. this has always been implemented by iterating a flattened dependency list built at dlopen time. however, the logic for building this list was completely wrong except in trivial cases; it simply used the list of libraries loaded since a given library, and their direct dependencies, as that library's dependencies, which could result in misordering, wrongful omission of deep dependencies from the search, and wrongful inclusion of unrelated libraries in the search. further, libraries did not have any recorded list of resolved dependencies until they were explicitly dlopened, meaning that DT_NEEDED entries had to be resolved again whenever a library participated as a dependency of more than one dlopened library. with this overhaul, the resolved direct dependency list of each library is always recorded when it is first loaded, and can be extended to a full flattened breadth-first search list if dlopen is called on the library. the extension is performed using the direct dependency list as a queue and appending copies of the direct dependency list of each dependency in the queue, excluding duplicates, until the end of the queue is reached. the direct deps remain available for future use as the initial subarray of the full deps array. first-load logic in dlopen is updated to match these changes, and clarified.
2019-02-27fix crash/misbehavior from oob read in new dynamic tls installationRich Felker-1/+1
code introduced in commit 9d44b6460ab603487dab4d916342d9ba4467e6b9 wrongly attempted to read past the end of the currently-installed dtv to determine if a dso provides new, not-already-installed tls. this logic was probably leftover from an earlier draft of the code that wrongly installed the new dtv before populating it. it would work if we instead queried the new, not-yet-installed dtv, but instead, replace the incorrect check with a simple range check against old_cnt. this also catches modules that have no tls at all with a single condition.
2019-02-25fix crash in new dynamic tls installation when last dep lacks tlsRich Felker-1/+4
code introduced in commit 9d44b6460ab603487dab4d916342d9ba4467e6b9 wrongly assumed the dso list tail was the right place to find new dtv storage. however, this is only true if the last-loaded dependency has tls. the correct place to get it is the dso corresponding to the tls module list tail. introduce a container_of macro to get it, and use it. ultimately, dynamic tls allocation should be refactored so that this is not an issue. there is no reason to be allocating new dtv space at each load_library; instead it could happen after all new libraries have been loaded but before they are committed. such changes may be made later, but this commit fixes the present regression.
2019-02-22add membarrier syscall wrapper, refactor dynamic tls install to use itRich Felker-32/+6
the motivation for this change is twofold. first, it gets the fallback logic out of the dynamic linker, improving code readability and organization. second, it provides application code that wants to use the membarrier syscall, which depends on preregistration of intent before the process becomes multithreaded unless unbounded latency is acceptable, with a symbol that, when linked, ensures that this registration happens.
2019-02-22fix loop logic cruft in dynamic tls installationRich Felker-1/+1
commit 9d44b6460ab603487dab4d916342d9ba4467e6b9 inadvertently contained leftover logic from a previous approach to the fallback signaling loop. it had no adverse effect, since j was always nonzero if the loop body was reachable, but it makes no sense to be there with the current approach to avoid signaling self.
2019-02-18install dynamic tls synchronously at dlopen, streamline accessRich Felker-42/+79
previously, dynamic loading of new libraries with thread-local storage allocated the storage needed for all existing threads at load-time, precluding late failure that can't be handled, but left installation in existing threads to take place lazily on first access. this imposed an additional memory access and branch on every dynamic tls access, and imposed a requirement, which was not actually met, that the dynamic tlsdesc asm functions preserve all call-clobbered registers before calling C code to to install new dynamic tls on first access. the x86[_64] versions of this code wrongly omitted saving and restoring of fpu/vector registers, assuming the compiler would not generate anything using them in the called C code. the arm and aarch64 versions saved known existing registers, but failed to be future-proof against expansion of the register file. now that we track live threads in a list, it's possible to install the new dynamic tls for each thread at dlopen time. for the most part, synchronization is not needed, because if a thread has not synchronized with completion of the dlopen, there is no way it can meaningfully request access to a slot past the end of the old dtv, which remains valid for accessing slots which already existed. however, it is necessary to ensure that, if a thread sees its new dtv pointer, it sees correct pointers in each of the slots that existed prior to the dlopen. my understanding is that, on most real-world coherency architectures including all the ones we presently support, a built-in consume order guarantees this; however, don't rely on that. instead, the SYS_membarrier syscall is used to ensure that all threads see the stores to the slots of their new dtv prior to the installation of the new dtv. if it is not supported, the same is implemented in userspace via signals, using the same mechanism as __synccall. the __tls_get_addr function, variants, and dynamic tlsdesc asm functions are all updated to remove the fallback paths for claiming new dynamic tls, and are now all branch-free.
2018-10-16add new stage 2b to dynamic linker bootstrap for thread pointerRich Felker-10/+23
commit a603a75a72bb469c6be4963ed1b55fabe675fe15 removed attribute const from __errno_location and pthread_self, and the same reasoning forced arch definitions of __pthread_self to use volatile asm, significantly impacting code generation and imposing manual caching of pointers where the impact might be noticable. reorder the thread pointer setup and place it across a strong barrier (symbolic function lookup) so that there is no assumed ordering between the initialization and the accesses to the thread pointer in stage 3.
2018-10-15fix misleading placement of statement on same line as for loop in ldsoRich Felker-1/+2
the placement triggered -Wmisleading-indentation warnings if enabled, and was gratuitously confusing to anyone reading the code.
2018-10-12fix dlsym of thread-local symbols on archs with DTP_OFFSET!=0Rich Felker-3/+3
commit 6ba5517a460c6c438f64d69464fdfc3269a4c91a modified __tls_get_addr to offset the address by +DTP_OFFSET (0x8000 on powerpc, mips, etc.) and adjusted the result of DTPREL relocations by -DTP_OFFSET to compensate, but missed changing the argument setup for calls to __tls_get_addr from dlsym.