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* simplify/shrink relocation processing in dynamic linker stage 1Rich Felker2015-05-251-24/+16
| | | | | | | | | the outer-loop approach made sense when we were also processing DT_JMPREL, which might be in REL or RELA form, to avoid major code duplication. commit 09db855b35709aa627d7055c57a98e1e471920ab removed processing of DT_JMPREL, and in the remaining two tables, the format (REL or RELA) is known by the name of the table. simply writing two versions of the loop results in smaller and simpler code.
* remove processing of DT_JMPREL from dynamic linker stage 1 bootstrapRich Felker2015-05-251-1/+0
| | | | | | | the DT_JMPREL relocation table necessarily consists entirely of JMP_SLOT (REL_PLT in internal nomenclature) relocations, which are symbolic; they cannot be resolved in stage 1, so there is no point in processing them.
* reprocess libc/ldso RELA relocations in stage 3 of dynamic linkingRich Felker2015-05-181-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | this fixes a regression on powerpc that was introduced in commit f3ddd173806fd5c60b3f034528ca24542aecc5b9. global data accesses on powerpc seem to be using a translation-unit-local GOT filled via R_PPC_ADDR32 relocations rather than R_PPC_GLOB_DAT. being a non-GOT relocation type, these were not reprocessed after adding the main application and its libraries to the chain, causing libc code not to see copy relocations in the main program, and therefore to use the pre-copy-relocation addresses for global data objects (like environ). the motivation for the dynamic linker only reprocessing GOT/PLT relocation types in stage 3 is that these types always have a zero addend, making them safe to process again even if the storage for the addend has been clobbered. other relocation types which can be used for address constants in initialized data objects may have non-zero addends which will be clobbered during the first pass of relocation processing if they're stored inline (REL form) rather than out-of-line (RELA form). powerpc generally uses only RELA, so this patch is sufficient to fix the regression in practice, but is not fully general, and would not suffice if an alternate toolchain generated REL for powerpc.
* remove always-true conditional in dynamic linker TLSDESC processingRich Felker2015-04-211-1/+1
| | | | | | the allocating path which can fail is for dynamic TLS, which can only occur at runtime, and the check for runtime was already made in the outer conditional.
* remove redundant code in do_dlsym functionRich Felker2015-04-211-1/+1
| | | | | | | commit 637dd2d383cc1f63bf02a732f03786857b22c7bd introduced the checks for RTLD_DEFAULT and RTLD_NEXT here, claiming they fixed a regression, but the above conditional block clearly already covered these cases, and removing the checks produces no difference in the generated code.
* make dlerror state and message thread-local and dynamically-allocatedRich Felker2015-04-181-32/+61
| | | | | | | | | this fixes truncation of error messages containing long pathnames or symbol names. the dlerror state was previously required by POSIX to be global. the resolution of bug 97 relaxed the requirements to allow thread-safe implementations of dlerror with thread-local state and message buffer.
* apply hidden visibility to tlsdesc accessor functionsRich Felker2015-04-175-0/+10
| | | | | | | these functions are never called directly; only their addresses are used, so PLT indirections should never happen unless a broken application tries to redefine them, but it's still best to make them hidden.
* comment fixes in aarch64 tlsdesc asmSzabolcs Nagy2015-04-171-4/+4
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* ensure debugger hook for dynamic linker does not point to a PLT slotRich Felker2015-04-171-2/+4
| | | | | this change is made in preparation to support linking without -Bsymbolic-functions.
* fix PLT call offset in sh dlsym asmRich Felker2015-04-171-3/+3
| | | | | | | | | | | the braf instruction's destination register is an offset from the address of the braf instruction plus 4 (or equivalently, the address of the next instruction after the delay slot). the code for dlsym was incorrectly computing the offset to pass using the address of the delay slot itself. in other places, a label was placed after the delay slot, but I find this confusing. putting the label on the branch instruction itself, and manually adding 4, makes it more clear which branch the offset in the constant pool goes with.
* fix sh build regressions in asmRich Felker2015-04-171-1/+1
| | | | | even hidden functions need @PLT symbol references; otherwise an absolute address is produced instead of a PC-relative one.
* use hidden __tls_get_new for tls/tlsdesc lookup fallback casesRich Felker2015-04-143-4/+10
| | | | | | | | | | | | | | | previously, the dynamic tlsdesc lookup functions and the i386 special-ABI ___tls_get_addr (3 underscores) function called __tls_get_addr when the slot they wanted was not already setup; __tls_get_addr would then in turn also see that it's not setup and call __tls_get_new. calling __tls_get_new directly is both more efficient and avoids the issue of calling a non-hidden (public API/ABI) function from asm. for the special i386 function, a weak reference to __tls_get_new is used since this function is not defined when static linking (the code path that needs it is unreachable in static-linked programs).
* use hidden visibility for call from dlsym to internal __dlsymRich Felker2015-04-1411-3/+14
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* fix inconsistent visibility for internal __tls_get_new functionRich Felker2015-04-141-0/+1
| | | | | | at the point of call it was declared hidden, but the definition was not hidden. for some toolchains this inconsistency produced textrels without ld-time binding.
* make _dlstart_c function use hidden visibilityRich Felker2015-04-141-0/+1
| | | | | otherwise the call/jump from the crt_arch.h asm may not resolve correctly without -Bsymbolic-functions.
* remove initializers for decoded aux/dyn arrays in dynamic linkerRich Felker2015-04-131-5/+5
| | | | | | | | the zero initialization is redundant since decode_vec does its own clearing, and it increases the risk that buggy compilers will generate calls to memset. as long as symbols are bound at ld time, such a call will not break anything, but it may be desirable to turn off ld-time binding in the future.
* remove remnants of support for running in no-thread-pointer modeRich Felker2015-04-131-10/+2
| | | | | | | | | | | | | since 1.1.0, musl has nominally required a thread pointer to be setup. most of the remaining code that was checking for its availability was doing so for the sake of being usable by the dynamic linker. as of commit 71f099cb7db821c51d8f39dfac622c61e54d794c, this is no longer necessary; the thread pointer is now valid before any libc code (outside of dynamic linker bootstrap functions) runs. this commit essentially concludes "phase 3" of the "transition path for removing lazy init of thread pointer" project that began during the 1.1.0 release cycle.
* move thread pointer setup to beginning of dynamic linker stage 3Rich Felker2015-04-131-8/+23
| | | | | | | | | | | | this allows the dynamic linker itself to run with a valid thread pointer, which is a prerequisite for stack protector on archs where the ssp canary is stored in TLS. it will also allow us to remove some remaining runtime checks for whether the thread pointer is valid. as long as the application and its libraries do not require additional size or alignment, this early thread pointer will be kept and reused at runtime. otherwise, a new static TLS block is allocated after library loading has finished and the thread pointer is switched over.
* stabilize dynamic linker's layout of static TLSRich Felker2015-04-131-9/+6
| | | | | | | | | | | | | | previously, the layout of the static TLS block was perturbed by the size of the dtv; dtv size increasing from 0 to 1 perturbed both TLS arch types, and the TLS-above-TP type's layout was perturbed by the specific number of dtv slots (libraries with TLS). this behavior made it virtually impossible to setup a tentative thread pointer address before loading libraries and keep it unchanged as long as the libraries' TLS size/alignment requirements fit. the new code fixes the location of the dtv and pthread structure at opposite ends of the static TLS block so that they will not move unless size or alignment changes.
* dynamic linker bootstrap overhaulRich Felker2015-04-1313-442/+281
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | this overhaul further reduces the amount of arch-specific code needed by the dynamic linker and removes a number of assumptions, including: - that symbolic function references inside libc are bound at link time via the linker option -Bsymbolic-functions. - that libc functions used by the dynamic linker do not require access to data symbols. - that static/internal function calls and data accesses can be made without performing any relocations, or that arch-specific startup code handled any such relocations needed. removing these assumptions paves the way for allowing libc.so itself to be built with stack protector (among other things), and is achieved by a three-stage bootstrap process: 1. relative relocations are processed with a flat function. 2. symbolic relocations are processed with no external calls/data. 3. main program and dependency libs are processed with a fully-functional libc/ldso. reduction in arch-specific code is achived through the following: - crt_arch.h, used for generating crt1.o, now provides the entry point for the dynamic linker too. - asm is no longer responsible for skipping the beginning of argv[] when ldso is invoked as a command. - the functionality previously provided by __reloc_self for heavily GOT-dependent RISC archs is now the arch-agnostic stage-1. - arch-specific relocation type codes are mapped directly as macros rather than via an inline translation function/switch statement.
* fix rpath string memory leak on failed dlopenRich Felker2015-04-041-0/+2
| | | | | | | | when dlopen fails, all partially-loaded libraries need to be unmapped and freed. any of these libraries using an rpath with $ORIGIN expansion may have an allocated string for the expanded rpath; previously, this string was not freed when freeing the library data structures.
* halt dynamic linker library search on errors resolving $ORIGIN in rpathRich Felker2015-04-031-8/+18
| | | | | | | | | | | | | | | this change hardens the dynamic linker against the possibility of loading the wrong library due to inability to expand $ORIGIN in rpath. hard failures such as excessively long paths or absence of /proc (when resolving /proc/self/exe for the main executable's origin) do not stop the path search, but memory allocation failures and any other potentially transient failures do. to implement this change, the meaning of the return value of fixup_rpath function is changed. returning zero no longer indicates that the dso's rpath string pointer is non-null; instead, the caller needs to check. a return value of -1 indicates a failure that should stop further path search.
* harden dynamic linker library path searchRich Felker2015-04-011-5/+16
| | | | | | | | | | | | transient errors during the path search should not allow the search to continue and possibly open the wrong file. this patch eliminates most conditions where that could happen, but there is still a possibility that $ORIGIN-based rpath processing will have an allocation failure, causing the search to skip such a path. fixing this is left as a separate task. a small bug where overly-long path components caused an infinite loop rather than being skipped/ignored is also fixed.
* add aarch64 portSzabolcs Nagy2015-03-113-0/+115
| | | | | | | | | | This adds complete aarch64 target support including bigendian subarch. Some of the long double math functions are known to be broken otherwise interfaces should be fully functional, but at this point consider this port experimental. Initial work on this port was done by Sireesh Tripurari and Kevin Bortis.
* copy the dtv pointer to the end of the pthread struct for TLS_ABOVE_TP archsSzabolcs Nagy2015-03-111-3/+3
| | | | | | | | | | | | | | | | | | | | There are two main abi variants for thread local storage layout: (1) TLS is above the thread pointer at a fixed offset and the pthread struct is below that. So the end of the struct is at known offset. (2) the thread pointer points to the pthread struct and TLS starts below it. So the start of the struct is at known (zero) offset. Assembly code for the dynamic TLSDESC callback needs to access the dynamic thread vector (dtv) pointer which is currently at the front of the pthread struct. So in case of (1) the asm code needs to hard code the offset from the end of the struct which can easily break if the struct changes. This commit adds a copy of the dtv at the end of the struct. New members must not be added after dtv_copy, only before it. The size of the struct is increased a bit, but there is opportunity for size optimizations.
* fix over-alignment of TLS, insufficient builtin TLS on 64-bit archsRich Felker2015-03-061-2/+8
| | | | | | | | | | | | | a conservative estimate of 4*sizeof(size_t) was used as the minimum alignment for thread-local storage, despite the only requirements being alignment suitable for struct pthread and void* (which struct pthread already contains). additional alignment required by the application or libraries is encoded in their headers and is already applied. over-alignment prevented the builtin_tls array from ever being used in dynamic-linked programs on 64-bit archs, thereby requiring allocation at startup even in programs with no TLS of their own.
* make all objects used with atomic operations volatileRich Felker2015-03-031-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | the memory model we use internally for atomics permits plain loads of values which may be subject to concurrent modification without requiring that a special load function be used. since a compiler is free to make transformations that alter the number of loads or the way in which loads are performed, the compiler is theoretically free to break this usage. the most obvious concern is with atomic cas constructs: something of the form tmp=*p;a_cas(p,tmp,f(tmp)); could be transformed to a_cas(p,*p,f(*p)); where the latter is intended to show multiple loads of *p whose resulting values might fail to be equal; this would break the atomicity of the whole operation. but even more fundamental breakage is possible. with the changes being made now, objects that may be modified by atomics are modeled as volatile, and the atomic operations performed on them by other threads are modeled as asynchronous stores by hardware which happens to be acting on the request of another thread. such modeling of course does not itself address memory synchronization between cores/cpus, but that aspect was already handled. this all seems less than ideal, but it's the best we can do without mandating a C11 compiler and using the C11 model for atomics. in the case of pthread_once_t, the ABI type of the underlying object is not volatile-qualified. so we are assuming that accessing the object through a volatile-qualified lvalue via casts yields volatile access semantics. the language of the C standard is somewhat unclear on this matter, but this is an assumption the linux kernel also makes, and seems to be the correct interpretation of the standard.
* adapt dynamic linker for new binutils versions that omit DT_RPATHRich Felker2014-11-231-0/+2
| | | | | | | | the new DT_RUNPATH semantics for search order are always used, and since binutils had always set both DT_RPATH and DT_RUNPATH when the latter was used, processing only DT_RPATH worked fine. however, recent binutils has stopped generating DT_RPATH when DT_RUNPATH is used, which broke support for this feature completely.
* save auxv pointer into libc struct early in dynamic linker startupRich Felker2014-11-191-0/+1
| | | | | this allows most code to assume it has already been saved, and is a prerequisite for upcoming changes for arm atomic/tls operations.
* add dlerror message for static-linked dlsym failureRich Felker2014-08-081-0/+2
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* fix dlerror when using dlopen with a static libcClément Vasseur2014-08-081-0/+2
| | | | | when the dynamic loader is disabled, dlopen fails correctly but dlerror did not return a human readable error string like it should have.
* add or1k (OpenRISC 1000) architecture portStefan Kristiansson2014-07-182-0/+39
| | | | | | | | | | | | | | | With the exception of a fenv implementation, the port is fully featured. The port has been tested in or1ksim, the golden reference functional simulator for OpenRISC 1000. It passes all libc-test tests (except the math tests that requires a fenv implementation). The port assumes an or1k implementation that has support for atomic instructions (l.lwa/l.swa). Although it passes all the libc-test tests, the port is still in an experimental state, and has yet experienced very little 'real-world' use.
* explicitly reject empty names in dynamic linker load_library functionRich Felker2014-07-111-0/+5
| | | | | | | | | previously passing an empty string for name resulted in failure, as expected, but only after spurious syscalls, and it produced confusing errno values (and thus dlerror strings). in addition to dlopen calls, this issue affected use of LD_PRELOAD with trailing whitespace or colon characters.
* make dynamic linker accept colon as a separator for LD_PRELOADRich Felker2014-07-111-2/+2
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* fix regression in mips dynamic linkerRich Felker2014-06-301-1/+6
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | this issue caused the address of functions in shared libraries to resolve to their PLT thunks in the main program rather than their correct addresses. it was observed causing crashes, though the mechanism of the crash was not thoroughly investigated. since the issue is very subtle, it calls for some explanation: on all well-behaved archs, GOT entries that belong to the PLT use a special relocation type, typically called JMP_SLOT, so that the dynamic linker can avoid having the jump destinations for the PLT resolve to PLT thunks themselves (they also provide a definition for the symbol, which must be used whenever the address of the function is taken so that all DSOs see the same address). however, the traditional mips PIC ABI lacked such a JMP_SLOT relocation type, presumably because, due to the way PIC works, the address of the PLT thunk was never needed and could always be ignored. prior to commit adf94c19666e687a728bbf398f9a88ea4ea19996, the mips version of reloc.h contained a hack that caused all symbol lookups to be treated like JMP_SLOT, inhibiting undefined symbols from ever being used to resolve symbolic relocations. this hack goes all the way back to commit babf820180368f00742ec65b2050a82380d7c542, when the mips dynamic linker was first made usable. during the recent refactoring to eliminate arch-specific relocation processing (commit adf94c19666e687a728bbf398f9a88ea4ea19996), this hack was overlooked and no equivalent functionality was provided in the new code. fixing the problem is not as simple as adding back an equivalent hack, since there is now also a "non-PIC ABI" that can be used for the main executable, which actually does use a PLT. the closest thing to official documentation I could find for this ABI is nonpic.txt, attached to Message-ID: 20080701202236.GA1534@caradoc.them.org, which can be found in the gcc mailing list archives and elsewhere. per this document, undefined symbols corresponding to PLT thunks have the STO_MIPS_PLT bit set in the symbol's st_other field. thus, I have added an arch-specific rule for mips, applied at the find_sym level rather than the relocation level, to reject undefined symbols with the STO_MIPS_PLT bit clear. the previous hack of treating all mips relocations as JMP_SLOT-like, rather than rejecting the unwanted symbols in find_sym, probably also caused dlsym to wrongly return PLT thunks in place of the correct address of a function under at least some conditions. this should now be fixed, at least for global-scope symbol lookups.
* fix regression in dynamic linker error reportingRich Felker2014-06-291-9/+5
| | | | | | due to a mistake when refactoring the error printing for the dynamic linker (commit 7c73cacd09a51a87484db5689864743e4984a84d), all messages were suppressed and replaced by blank lines.
* rename dynamic linker _start to _dlstart in the stub versionRich Felker2014-06-231-1/+1
| | | | | the renaming was previously applied to all real versions of the function in commit 3fa2eb2aba8d6b54dec53e7ad4c37e17392b166f.
* rename dynamic linker entry point from _start to _dlstartRich Felker2014-06-208-19/+19
| | | | | | the main motivation for this change is to aid in debugging. since the main program's entry point is also named _start, it was difficult to set breakpoints or quickly identify which _start execution stopped in.
* add tlsdesc support for x86_64Rich Felker2014-06-191-0/+40
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* separate __tls_get_addr implementation from dynamic linker/init_tlsRich Felker2014-06-191-6/+6
| | | | | | | | | | | | | | | such separation serves multiple purposes: - by having the common path for __tls_get_addr alone in its own function with a tail call to the slow case, code generation is greatly improved. - by having __tls_get_addr in it own file, it can be replaced on a per-arch basis as needed, for optimization or ABI-specific purposes. - by removing __tls_get_addr from __init_tls.c, a few bytes of code are shaved off of static binaries (which are unlikely to use this function unless the linker messed up).
* add tlsdesc support for i386Rich Felker2014-06-191-0/+27
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* change dynamic TLS installation strategy to optimize accessRich Felker2014-06-191-8/+14
| | | | | | | | | | | | | | | previously, accesses to dynamic TLS had to check two conditions before being able to use a dtv slot: (1) that the module index was within the bounds of the current dtv size, and (2) that the dynamic tls for the requested module index was already installed in the dtv. this commit changes the installation strategy so that, whenever an attempt is made to access dynamic TLS that's not yet installed in the dtv, the dynamic TLS for all lower-index modules is also installed. thus it provides a new invariant: if a given module index is within the bounds of the current dtv size, we automatically know that its TLS is installed and directly available. the requirement that the second condition (above) be checked is eliminated.
* add arch-generic support for tlsdesc relocations to dynamic linkerRich Felker2014-06-192-0/+54
| | | | | | this code is non-functional without further changes to link up the arch-specific reloc types for tlsdesc and add asm implementations of __tlsdesc_static and __tlsdesc_dynamic.
* reduce code duplication in dynamic linker error pathsRich Felker2014-06-181-16/+16
| | | | eventually this should help making dlerror thread-safe too.
* refactor to remove arch-specific relocation code from dynamic linkerRich Felker2014-06-181-8/+89
| | | | | | | | | | | this was one of the main instances of ugly code duplication: all archs use basically the same types of relocations, but roughly equivalent logic was duplicated for each arch to account for the different naming and numbering of relocation types and variation in whether REL or RELA records are used. as an added bonus, both REL and RELA are now supported on all archs, regardless of which is used by the standard toolchain.
* add options when explicitly invoking dynamic loaderRich Felker2014-04-161-2/+21
| | | | | | | | | so far the options are --library-path and --preload which override the corresponding environment variables, and --list which forces the behavior of ldd even if the invocation name is not ldd. both the two-arg form and the one-arg form using an equals sign are supported. based loosely on a patch proposed by Rune.
* remove lazy ssp initializationTimo Teräs2014-03-251-13/+0
| | | | | | | | now that thread pointer is initialized always, ssp canary initialization can be done unconditionally. this simplifies the ldso as it does not try to detect ssp usage, and the init function itself as it is always called exactly once. this also merges ssp init path for shared and static linking.
* if dynamic linker's relro mprotect call fails, include reason in messageRich Felker2014-03-251-1/+1
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* cosmetic improvements in dynamic linker cleanupRich Felker2014-03-251-5/+5
| | | | consistent use of braces in if/else structure, line length.
* clean up internal dynamic linker functions enumerating phdrsTimo Teräs2014-03-251-28/+23
| | | | | | | | record phentsize in struct dso, so the phdrs can be easily enumerated via it. simplify all functions enumerating phdrs to require only struct dso. also merge find_map_range and find_dso to kernel_mapped_dso function that does both tasks during single phdr enumeration.