path: root/src/ldso
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2014-06-23rename dynamic linker _start to _dlstart in the stub versionRich Felker-1/+1
the renaming was previously applied to all real versions of the function in commit 3fa2eb2aba8d6b54dec53e7ad4c37e17392b166f.
2014-06-20rename dynamic linker entry point from _start to _dlstartRich Felker-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.
2014-06-19add tlsdesc support for x86_64Rich Felker-0/+40
2014-06-19separate __tls_get_addr implementation from dynamic linker/init_tlsRich Felker-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).
2014-06-19add tlsdesc support for i386Rich Felker-0/+27
2014-06-19change dynamic TLS installation strategy to optimize accessRich Felker-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.
2014-06-19add arch-generic support for tlsdesc relocations to dynamic linkerRich Felker-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.
2014-06-18reduce code duplication in dynamic linker error pathsRich Felker-16/+16
eventually this should help making dlerror thread-safe too.
2014-06-18refactor to remove arch-specific relocation code from dynamic linkerRich Felker-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.
2014-04-16add options when explicitly invoking dynamic loaderRich Felker-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.
2014-03-25remove lazy ssp initializationTimo Teräs-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.
2014-03-25if dynamic linker's relro mprotect call fails, include reason in messageRich Felker-1/+1
2014-03-25cosmetic improvements in dynamic linker cleanupRich Felker-5/+5
consistent use of braces in if/else structure, line length.
2014-03-25clean up internal dynamic linker functions enumerating phdrsTimo Teräs-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.
2014-03-25implement PT_GNU_RELRO supportTimo Teräs-15/+37
2014-03-24always initialize thread pointer at program startRich Felker-9/+19
this is the first step in an overhaul aimed at greatly simplifying and optimizing everything dealing with thread-local state. previously, the thread pointer was initialized lazily on first access, or at program startup if stack protector was in use, or at certain random places where inconsistent state could be reached if it were not initialized early. while believed to be fully correct, the logic was fragile and non-obvious. in the first phase of the thread pointer overhaul, support is retained (and in some cases improved) for systems/situation where loading the thread pointer fails, e.g. old kernels. some notes on specific changes: - the confusing use of libc.main_thread as an indicator that the thread pointer is initialized is eliminated in favor of an explicit has_thread_pointer predicate. - sigaction no longer needs to ensure that the thread pointer is initialized before installing a signal handler (this was needed to prevent a situation where the signal handler caused the thread pointer to be initialized and the subsequent sigreturn cleared it again) but it still needs to ensure that implementation-internal thread-related signals are not blocked. - pthread tsd initialization for the main thread is deferred in a new manner to minimize bloat in the static-linked __init_tp code. - pthread_setcancelstate no longer needs special handling for the situation before the thread pointer is initialized. it simply fails on systems that cannot support a thread pointer, which are non-conforming anyway. - pthread_cleanup_push/pop now check for missing thread pointer and nop themselves out in this case, so stdio no longer needs to avoid the cancellable path when the thread pointer is not available. a number of cases remain where certain interfaces may crash if the system does not support a thread pointer. at this point, these should be limited to pthread interfaces, and the number of such cases should be fewer than before.
2014-02-27rename superh port to "sh" for consistencyRich Felker-0/+0
linux, gcc, etc. all use "sh" as the name for the superh arch. there was already some inconsistency internally in musl: the dynamic linker was searching for "ld-musl-sh.path" as its path file despite its own name being "". there was some sentiment in both directions as to how to resolve the inconsistency, but overall "sh" was favored.
2014-02-23superh portBobby Bingham-0/+36
2014-02-23x32 port (diff against vanilla x86_64)rofl0r-7/+15
2014-02-23import vanilla x86_64 code as x32rofl0r-0/+22
2014-01-21fix crash in dynamic linker when certain copy relocations are unsatisfiedRich Felker-1/+2
STB_WEAK is only a weak reference for undefined symbols (those with a section of SHN_UNDEF). otherwise, it's a weak definition. normally this distinction would not matter, since a relocation referencing a symbol that also provides a definition (not SHN_UNDEF) will always succeed in finding the referenced symbol itself. however, in the case of copy relocations, the referenced symbol itself is ignored in order to search for another symbol to copy from, and thus it's possible that no definition is found. in this case, if the symbol being resolved happened to be a weak definition, it was misinterpreted as a weak reference, suppressing the error path and causing a crash when the copy relocation was performed with a null source pointer passed to memcpy. there are almost certainly still situations in which invalid combinations of symbol and relocation types can cause the dynamic linker to crash (this is pretty much inevitable), but the intent is that crashes not be possible for symbol/relocation tables produced by a valid linker.
2014-01-06const-qualify the address argument to dladdrRich Felker-4/+4
this agrees with implementation practice on glibc and BSD systems, and is the const-correct way to do things; it eliminates warnings from passing pointers to const. the prototype without const came from seemingly erroneous man pages.
2013-12-14fix dynamic linker entry point for microblazeRich Felker-3/+4
the ABI allows the callee to clobber stack slots that correspond to arguments passed in registers, so the caller must adjust the stack pointer to reserve space appropriately. prior to this fix, the argv array was possibly clobbered by dynamic linker code before passing control to the main program.
2013-12-12include cleanups: remove unused headers and add feature test macrosSzabolcs Nagy-0/+1
2013-12-01add infrastructure to record and report the version of libc.soRich Felker-2/+7
this is still experimental and subject to change. for git checkouts, an attempt is made to record the exact revision to aid in bug reports and debugging. no version information is recorded in the static libc.a or binaries it's linked into.
2013-11-25remove duplicate includes from dynlink.c, strfmon.c and getaddrinfo.cSzabolcs Nagy-3/+0
2013-10-04fix uninitialized variable in dladdrRich Felker-1/+1
the affected branch only applies for DSOs that lack standard hash table and only have the GNU hash table present.
2013-09-15support configurable page size on mips, powerpc and microblazeSzabolcs Nagy-0/+1
PAGE_SIZE was hardcoded to 4096, which is historically what most systems use, but on several archs it is a kernel config parameter, user space can only know it at execution time from the aux vector. PAGE_SIZE and PAGESIZE are not defined on archs where page size is a runtime parameter, applications should use sysconf(_SC_PAGE_SIZE) to query it. Internally libc code defines PAGE_SIZE to libc.page_size, which is set to aux[AT_PAGESZ] in __init_libc and early in __dynlink as well. (Note that libc.page_size can be accessed without GOT, ie. before relocations are done) Some fpathconf settings are hardcoded to 4096, these should be actually queried from the filesystem using statfs.
2013-09-09do not use default when dynamic linker fails to open existing path fileRich Felker-0/+2
if fopen fails for a reason other than ENOENT, we must assume the intent is that the path file be used. failure may be due to misconfiguration or intentional resource-exhaustion attack (against suid programs), in which case falling back to loading libraries from an unintended path could be dangerous.
2013-08-23make dlopen honor the rpath of the main programRich Felker-1/+1
this seems to match what other systems do, and seems useful for programs that have their libraries and plugins stored relative to the executable.
2013-08-23fix bugs in $ORIGIN handlingRich Felker-3/+9
1. an occurrence of ${ORIGIN} before $ORIGIN would be ignored due to the strstr logic. (note that rpath contains multiple :-delimited paths to be searched.) 2. data read by readlink was not null-terminated.
2013-08-23use AT_EXECFN, if available, for dynamic linker to identify main programRich Felker-1/+5
fallback to argv[0] as before. unlike argv[0], AT_EXECFN was a valid (but possibly relative) pathname for the new program image at the time the execve syscall was made. as a special case, ignore AT_EXECFN if it begins with "/proc/", in order not to give bogus (and possibly harmful) results when fexecve was used.
2013-08-23add rpath $ORIGIN processing to dynamic linkerRich Felker-3/+59
2013-08-23add recursive rpath support to dynamic linkerRich Felker-12/+13
previously, rpath was only honored for direct dependencies. in other words, if A depends on B and B depends on C, only B's rpath (if any), not A's rpath, was being searched for C. this limitation made rpath-based deployment difficult in the presence of multiple levels of library dependency. at present, $ORIGIN processing in rpath is still unsupported.
2013-08-08work around libraries with versioned symbols in dynamic linkerRich Felker-11/+14
this commit does not add versioning support; it merely fixes incorrect lookups of symbols in libraries that contain versioned symbols. previously, the version information was completely ignored, and empirically this seems to have resulted in the oldest version being chosen, but I am uncertain if that behavior was even reliable. the new behavior being introduced is to completely ignore symbols which are marked "hidden" (this seems to be the confusing nomenclature for non-current-version) when versioning is present. this should solve all problems related to libraries with symbol versioning as long as all binaries involved are up-to-date (compatible with the latest-version symbols), and it's the needed behavior for dlsym under all circumstances.
2013-08-03add system for resetting TLS to initial valuesRich Felker-0/+13
this is needed for reused threads in the SIGEV_THREAD timer notification system, and could be reused elsewhere in the future if needed, though it should be refactored for such use. for static linking, __init_tls.c is simply modified to export the TLS info in a structure with external linkage, rather than using statics. this perhaps makes the code more clear, since the statics were poorly named for statics. the new __reset_tls.c is only linked if it is used. for dynamic linking, the code is in dynlink.c. sharing code with __copy_tls is not practical since __reset_tls must also re-zero thread-local bss.
2013-08-02move RPATH search after LD_LIBRARY_PATH searchRich Felker-2/+2
this is the modern way, and the only way that makes any sense. glibc has this complicated mechanism with RPATH and RUNPATH that controls whether RPATH is processed before or after LD_LIBRARY_PATH, presumably to support legacy binaries, but there is no compelling reason to support this, and better behavior is obtained by just fixing the search order.
2013-08-02if map_library has allocated a buffer for phdrs, free it on success tooRich Felker-0/+1
this fixes an oversight in the previous commit.
2013-08-02improve error handling in map_library and support long phdrsRich Felker-12/+21
previously, errno could be meaningless when the caller wrote it to the dlerror string or stderr. try to make it meaningful. also, fix incorrect check for over-long program headers and instead actually support them by allocating memory if needed.
2013-08-02fix uninitialized dyn variable in map_libraryRich Felker-1/+1
this can only happen for invalid library files, but they were not detected reliably because the variable was uninitialized.
2013-07-31fix theoretical out-of-bound access in dynamic linkerRich Felker-1/+1
one of the arguments to memcmp may be shorter than the length l-3, and memcmp is under no obligation not to access past the first byte that differs. instead use strncmp which conveys the correct semantics. the performance difference is negligible here and since the code is only use for shared libc, both functions are already linked anyway.
2013-07-31prevent passing PT_INTERP name to dlopen from double-loading libcRich Felker-6/+11
the dev/inode for the main app and the dynamic linker ("interpreter") are not available, so the subsequent checks don't work. in general we don't want to make exact string matches to existing libraries prevent loading new ones, since this breaks loading upgraded modules in module-loading systems. so instead, special-case it. the motivation for this fix is that calling dlopen on the names returned by dl_iterate_phdr or walking the link map (obtained by dlinfo) seem to be the only methods available to an application to actually get a list of open dso handles.
2013-07-31add some sanity checks in dynamic loader codeRich Felker-0/+10
reject elf files which are not ET_EXEC/ET_DYN type as bad exec format, and reject ET_EXEC files when they cannot be loaded at the correct address, since they are not relocatable at runtime. the main practical benefit of this is to make dlopen of the main program fail rather than producing an unsafe-to-use handle.
2013-07-31fix bug where read error was treated as success reading library headersRich Felker-1/+1
2013-07-31don't call null pointer if DT_INIT/DT_FINI are nullRich Felker-2/+2
it's not clear to me why the linker even outputs these headers if they are null, but apparently it does so. with the default startfiles, they will never be null anyway, but this patch allows eliminating crti, crtn, crtbegin, and crtend (leaving only crt1) if the toolchain is using init_array/fini_array (or for a C-only, no-ctor environment).
2013-07-27fix indention-with-spacesRich Felker-1/+1
2013-07-26make ldd report the libc/dynamic linker itselfRich Felker-0/+22
2013-07-26fix computation of entry point and main app phdrs when invoking via ldsoRich Felker-3/+1
entry point was wrong for PIE. e_entry was being treated as an absolute value, whereas it's actually relative to the load address (which is zero for non-PIE). phdr pointer was wrong for non-PIE. e_phoff was being treated as load-address-relative, whereas it's actually a file offset in the ELF file. in any case, map_library was already computing it correctly, and the incorrect code in __dynlink was overwriting it with junk.
2013-07-24support STB_GNU_UNIQUE symbol bindings in dynamic linkerRich Felker-1/+1
these are needed for some C++ library binaries including most builds of libstdc++. I'm not entirely clear on the rationale. this patch does not implement any special semantics for them, but as far as I can tell, no special treatment is needed in correctly-linked programs; this binding seems to exist only for catching incorrectly-linked programs.
2013-07-24move the dynamic linker's jmp_buf from static to automatic storageRich Felker-5/+7
this more than compensates for the size increase of jmp_buf, and greatly reduces bss/data size on archs with huge jmp_buf.