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* add real fdpic loading of shared librariesRich Felker2015-09-222-9/+58
| | | | | | previously, the normal ELF library loading code was used even for fdpic, so only the kernel-loaded dynamic linker and main app could benefit from separate placement of segments and shared text.
* add general fdpic support in dynamic linker and arch support for shRich Felker2015-09-223-14/+202
| | | | | | | | | | | | | | | | | | at this point not all functionality is complete. the dynamic linker itself, and main app if it is also loaded by the kernel, take advantage of fdpic and do not need constant displacement between segments, but additional libraries loaded by the dynamic linker follow normal ELF semantics for mapping still. this fully works, but does not admit shared text on nommu. in terms of actual functional correctness, dlsym's results are presently incorrect for function symbols, RTLD_NEXT fails to identify the caller correctly, and dladdr fails almost entirely. with the dynamic linker entry point working, support for static pie is automatically included, but linking the main application as ET_DYN (pie) probably does not make sense for fdpic anyway. ET_EXEC is equally relocatable but more efficient at representing relocations.
* factor symbol counting out of dladdr as its own functionRich Felker2015-09-211-19/+20
| | | | | | | | | | | | | the fdpic code will need to count symbols, and it may be useful elsewhere in the future too. counting is trivial as long as sysv hash is present, but for gnu-hash-only libraries it's complex. the behavior of the count is changed slightly: we now include symbols that are not accessible by the gnu hash table in the count. this may make dladdr slightly slower. if this is a problem, dladdr can subtract out the part that should not be accessible. unlike in the old code, subtracting this out is easy even in the fast path where sysv hash is available too.
* simplify dlstart code by using integer type for base addressRich Felker2015-09-211-8/+7
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* refactor some more dynamic linker load address computationsRich Felker2015-09-171-7/+7
| | | | these were just missed in the previous commits.
* remove some useless casts in dynamic linkerRich Felker2015-09-171-2/+2
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* add fdpic structs and reloc types for dynamic linkingRich Felker2015-09-171-0/+16
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* further refactoring of dynamic linker load address computationsRich Felker2015-09-171-2/+2
| | | | | | | these are in do_relocs. the first one was omitted in commit 301335a80b85f12c018e4acf1a2c28615e119f8d because it slightly changes code (using dso->base rather than cached local var base) and would have prevented easy verification. the other was an oversight.
* begin refactoring load address computations in dynamic linkerRich Felker2015-09-171-19/+22
| | | | | | | | | | | | | for ordinary ELF with fixed segment displacements, load address computation is simply adding the base load address. but for FDPIC, each segment has its own load address, and virtual addresses need to be adjusted according to the segment they fall in. abstracting this computation is the first step to making the dynamic linker ready for FDPIC. for this first commit, a macro is used rather than a function in order to facilitate correctness checking. I have verified that the generated code does not change on my i386 build.
* remove old dlstart stage-2 symbolic lookup code; add new genericRich Felker2015-09-171-14/+8
| | | | | | | | | | | | | | this new generic version of the stage-2 function lookup should work for any arch where static data is accessible via got-relative or pc-relative addressing, using approximately the technique described in the log message for commit 2907afb8dbd4c1d34825c3c9bd2b41564baca210. since all the mips-like archs that need got slots fo access static data have already transitioned to the new stage chaining scheme, the old dynamic symbol lookup code is now removed. aarch64, arm, and sh have not yet transitioned; with this commit, they are now using the new generic code.
* introduce new symbol-lookup-free rcrt1/dlstart stage chainingRich Felker2015-09-171-0/+6
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | previously, the call into stage 2 was made by looking up the symbol name "__dls2" (which was chosen short to be easy to look up) from the dynamic symbol table. this was no problem for the dynamic linker, since it always exports all its symbols. in the case of the static pie entry point, however, the dynamic symbol table does not contain the necessary symbol unless -rdynamic/-E was used when linking. this linking requirement is a major obstacle both to practical use of static-pie as a nommu binary format (since it greatly enlarges the file) and to upstream toolchain support for static-pie (adding -E to default linking specs is not reasonable). this patch replaces the runtime symbolic lookup with a link-time lookup via an inline asm fragment, which reloc.h is responsible for providing. in this initial commit, the asm is provided only for i386, and the old lookup code is left in place as a fallback for archs that have not yet transitioned. modifying crt_arch.h to pass the stage-2 function pointer as an argument was considered as an alternative, but such an approach would not be compatible with fdpic, where it's impossible to compute function pointers without already having performed relocations. it was also deemed desirable to keep crt_arch.h as simple/minimal as possible. in principle, archs with pc-relative or got-relative addressing of static variables could instead load the stage-2 function pointer from a static volatile object. that does not work for fdpic, and is not safe against reordering on mips-like archs that use got slots even for static functions, but it's a valid on i386 and many others, and could provide a reasonable default implementation in the future.
* provide arch-generic fdpic self-relocation code for crt1 to useRich Felker2015-09-121-0/+28
| | | | | this file is intended to be included by crt_arch.h on fdpic-based targets and needs to be called from the entry point asm.
* make sh clone asm fdpic-compatibleRich Felker2015-09-121-3/+9
| | | | | | | | | | | clone calls back to a function pointer provided by the caller, which will actually be a pointer to a function descriptor on fdpic. the obvious solution is to have a separate version of clone for fdpic, but I have taken a simpler approach to go around the problem. instead of calling the pointed-to function from asm, a direct call is made to an internal C function which then calls the pointed-to function. this lets the C compiler generate the appropriate calling convention for an indirect call with no need for ABI-specific assembly.
* fix uninitialized scopeid in lookups from hosts file and ip literalsTimo Teräs2015-09-111-2/+2
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* remove unused (and invalid) C version of sigsetjmpRich Felker2015-09-091-17/+0
| | | | | | | | | originally, the comment in this code was correct and it would likely work if the compiler generated a tail call to setjmp. however, commit 583e55122e767b1586286a0d9c35e2a4027998ab redesigned sigsetjmp and siglongjmp such that the old C implementation (which was not intended to be used) is not even conceptually correct. remove it in the interest of avoiding confusion when porting to new archs.
* fix breakage in nl_langinfo from previous commitRich Felker2015-09-091-1/+1
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* make nl_langinfo(CODESET) always return "UTF-8"Rich Felker2015-09-091-2/+1
| | | | | | | | | | | | | | | | | | | | | | | this restores the original behavior prior to the addition of the byte-based C locale and fixes what is effectively a regression in musl's property of always providing working UTF-8 support. commit 1507ebf837334e9e07cfab1ca1c2e88449069a80 introduced the codeset name "UTF-8-CODE-UNITS" for the byte-based C locale to represent that the semantic content is UTF-8 but that it is being processed as code units (bytes) rather than whole multibyte characters. however, many programs assume that the codeset name is usable with iconv and/or comes from a set of standard/widely-used names known to the application. such programs are likely to produce warnings or errors, run with reduced functionality, or mangle character data when run explicitly in the C locale. the standard places basically no requirements for the string returned by nl_langinfo(CODESET) and how it interacts with other interfaces, so returning "UTF-8" is permissible. moreover, it seems like the right thing to do, since the identity of the character encoding as "UTF-8" is independent of whether it is being processed as bytes of characters by the standard library functions.
* fix fclose of permanent (stdin/out/err) streamsRich Felker2015-09-091-2/+3
| | | | | | | | | | | | | | | | this fixes a bug reported by Nuno Gonçalves. previously, calling fclose on stdin or stdout resulted in deadlock at exit time, since __stdio_exit attempts to lock these streams to flush/seek them, and has no easy way of knowing that they were closed. conceptually, leaving a FILE stream locked on fclose is valid since, in the abstract machine, it ceases to exist. but to satisfy the implementation-internal assumption in __stdio_exit that it can access these streams unconditionally, we need to unlock them. it's also necessary that fclose leaves permanent streams in a state where __stdio_exit will not attempt any further operations on them. fortunately, the call to fflush already yields this property.
* getsubopt: don't include leading = in value stringSteven Barth2015-08-211-1/+1
| | | | | | | getsubopt incorrectly returns the delimiting = in the value string, this patch fixes it by increasing the pointer position by one. Signed-off-by: Steven Barth <cyrus@openwrt.org>
* match historical behavior for tm_gmtoff member of struct tmNatanael Copa2015-08-144-12/+12
| | | | | | | | | | | | | | tm_gmtoff is a nonstandard field, but on historical systems which have this field, it stores the offset of the local time zone from GMT or UTC. this is the opposite of the POSIX extern long timezone object and the offsets used in POSIX-form TZ strings, which represent the offset from local time to UTC. previously we were storing these negated offsets in tm_gmtoff too. programs which only used this field indirectly via strftime were not affected since strftime performed the negation for presentation. however, some programs and libraries accesse tm_gmtoff directly and were obtaining negated time zone offsets.
* fix failure of tempnam to null-terminate resultRich Felker2015-08-091-0/+1
| | | | | | | tempnam uses an uninitialized buffer which is filled using memcpy and __randname. It is therefore necessary to explicitly null-terminate it. based on patch by Felix Janda.
* mitigate blow-up of heap size under malloc/free contentionRich Felker2015-08-071-14/+14
| | | | | | | | | | | | | | | | | | | | | | | during calls to free, any free chunks adjacent to the chunk being freed are momentarily held in allocated state for the purpose of merging, possibly leaving little or no available free memory for other threads to allocate. under this condition, other threads will attempt to expand the heap rather than waiting to use memory that will soon be available. the race window where this happens is normally very small, but became huge when free chooses to use madvise to release unused physical memory, causing unbounded heap size growth. this patch drastically shrinks the race window for unwanted heap expansion by performing madvise with the bin lock held and marking the bin non-empty in the binmask before making the expensive madvise syscall. testing by Timo Teräs has shown this approach to be a suitable mitigation. more invasive changes to the synchronization between malloc and free would be needed to completely eliminate the problem. it's not clear whether such changes would improve or worsen typical-case performance, or whether this would be a worthwhile direction to take malloc development.
* fix undefined left-shift of negative values in utf-8 state tableRich Felker2015-07-251-1/+1
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* fix atexit when it is called from an atexit handlerRich Felker2015-07-241-12/+9
| | | | | | | | | | | | | | | The old code accepted atexit handlers after exit, but did not run them reliably. C11 seems to explicitly allow atexit to fail (and report such failure) in this case, but this situation can easily come up in C++ if a destructor has a local static object with a destructor so it should be handled. Note that the memory usage can grow linearly with the overall number of registered atexit handlers instead of with the worst case list length. (This only matters if atexit handlers keep registering atexit handlers which should not happen in practice). Commit message/rationale based on text by Szabolcs Nagy.
* handle loss of syslog socket connectionRich Felker2015-07-091-7/+11
| | | | | | | | | | | | | | | | | | | | | | | | | when traditional syslogd implementations are restarted, the old server socket ceases to exist and a new unix socket with the same pathname is created. when this happens, the default destination address associated with the client socket via connect is no longer valid, and attempts to send produce errors. this happens despite the socket being datagram type, and is in contrast to the behavior that would be seen with an IP datagram (UDP) socket. in order to avoid a situation where the application is unable to send further syslog messages without calling closelog, this patch makes syslog attempt to reconnect the socket when send returns an error indicating a lost connection. additionally, initial failure to connect the socket no longer results in the socket being closed. this ensures that an application which calls openlog to reserve the socket file descriptor will not run into a situation where transient connection failure (e.g. due to syslogd restart) prevents fd reservation. however, applications which may be unable to connect the socket later (e.g. due to chroot, restricted permissions, seccomp, etc.) will still fail to log if the syslog socket cannot be connected at openlog time or if it has to be reconnected later.
* fix incorrect void return type for syncfs functionRich Felker2015-07-091-2/+2
| | | | | | being nonstandard, the closest thing to a specification for this function is its man page, which documents it as returning int. it can fail with EBADF if the file descriptor passed is invalid.
* fix negated return value of ns_skiprr, breakage in related functionsRich Felker2015-07-081-1/+1
| | | | | | | | due to a reversed pointer difference computation, ns_skiprr always returned a negative value, which functions using it would interpret as an error. patch by Yu Lu.
* treat empty TZ environment variable as GMT rather than defaultRich Felker2015-07-061-1/+2
| | | | | | this improves compatibility with the behavior of other systems and with some applications which set an empty TZ var to disable use of local time by mktime, etc.
* dynlink.c: pass gnu-hash table pointer to gnu_lookupAlexander Monakov2015-06-281-13/+11
| | | | | | | | | | The callers need to check the value of the pointer anyway, so make them pass the pointer to gnu_lookup instead of reloading it there. Reorder gnu_lookup arguments so that always-used ones are listed first. GCC can choose a calling convention with arguments in registers (e.g. up to 3 arguments in eax, ecx, edx on x86), but cannot reorder the arguments for static functions.
* dynlink.c: slim down gnu_lookupAlexander Monakov2015-06-281-9/+5
| | | | | Do not reference dso->syms and dso->strings until point of use. Check 'h1 == (h2|1)', the simplest condition, before the others.
* dynlink.c: use bloom filter in gnu hash lookupAlexander Monakov2015-06-281-3/+22
| | | | | | | | Introduce gnu_lookup_filtered and use it to speed up symbol lookups in find_sym (do_dlsym is left as is, based on an expectation that frequently dlsym queries will use a dlopen handle rather than RTLD_NEXT or RTLD_DEFAULT, and will not need to look at more than one DSO).
* dynlink.c: use a faster expression in gnu_hashAlexander Monakov2015-06-271-1/+1
| | | | | With -Os, GCC uses a multiply rather than a shift and addition for 'h*33'. Use a more efficient expression explicitely.
* fix local-dynamic model TLS on mips and powerpcRich Felker2015-06-253-5/+9
| | | | | | | | | | | | | | | | | | | | | | | | | | the TLS ABI spec for mips, powerpc, and some other (presently unsupported) RISC archs has the return value of __tls_get_addr offset by +0x8000 and the result of DTPOFF relocations offset by -0x8000. I had previously assumed this part of the ABI was actually just an implementation detail, since the adjustments cancel out. however, when the local dynamic model is used for accessing TLS that's known to be in the same DSO, either of the following may happen: 1. the -0x8000 offset may already be applied to the argument structure passed to __tls_get_addr at ld time, without any opportunity for runtime relocations. 2. __tls_get_addr may be used with a zero offset argument to obtain a base address for the module's TLS, to which the caller then applies immediate offsets for individual objects accessed using the local dynamic model. since the immediate offsets have the -0x8000 adjustment applied to them, the base address they use needs to include the +0x8000 offset. it would be possible, but more complex, to store the pointers in the dtv[] array with the +0x8000 offset pre-applied, to avoid the runtime cost of adding 0x8000 on each call to __tls_get_addr. this change could be made later if measurements show that it would help.
* make dynamic linker work around MAP_FAILED mmap failure on nommu kernelsRich Felker2015-06-231-2/+24
| | | | | | previously, loading of additional libraries beyond libc/ldso did not work on nommu kernels, nor did loading programs via invocation of the dynamic linker as a command.
* reimplement strverscmp to fix corner casesRich Felker2015-06-231-32/+25
| | | | | | | | | | | | | | | | | this interface is non-standardized and is a GNU invention, and as such, our implementation should match the behavior of the GNU function. one peculiarity the old implementation got wrong was the handling of all-zero digit sequences: they are supposed to compare greater than digit sequences of which they are a proper prefix, as in 009 < 00. in addition, high bytes were treated with char signedness rather than as unsigned. this was wrong regardless of what the GNU function does since the resulting order relation varied by arch. the new strverscmp implementation makes explicit the cases where the order differs from what strcmp would produce, of which there are only two.
* fix regression/typo that disabled __simple_malloc when calloc is usedRich Felker2015-06-221-1/+1
| | | | | | commit ba819787ee93ceae94efd274f7849e317c1bff58 introduced this regression. since the __malloc0 weak alias was not properly provided by __simple_malloc, use of calloc forced the full malloc to be linked.
* fix calloc when __simple_malloc implementation is usedRich Felker2015-06-223-12/+15
| | | | | | | | | | | | | | | | | previously, calloc's implementation encoded assumptions about the implementation of malloc, accessing a size_t word just prior to the allocated memory to determine if it was obtained by mmap to optimize out the zero-filling. when __simple_malloc is used (static linking a program with no realloc/free), it doesn't matter if the result of this check is wrong, since all allocations are zero-initialized anyway. but the access could be invalid if it crosses a page boundary or if the pointer is not sufficiently aligned, which can happen for very small allocations. this patch fixes the issue by moving the zero-fill logic into malloc.c with the full malloc, as a new function named __malloc0, which is provided by a weak alias to __simple_malloc (which always gives zero-filled memory) when the full malloc is not in use.
* provide __stack_chk_fail_local in libc.aRich Felker2015-06-201-0/+4
| | | | | | | | | | | | | | this symbol is needed only on archs where the PLT call ABI is klunky, and only for position-independent code compiled with stack protector. thus references usually only appear in shared libraries or PIE executables, but they can also appear when linking statically if some of the object files being linked were built as PIC/PIE. normally libssp_nonshared.a from the compiler toolchain should provide __stack_chk_fail_local, but reportedly it appears prior to -lc in the link order, thus failing to satisfy references from libc itself (which arise only if libc.a was built as PIC/PIE with stack protector enabled).
* work around mips detached thread exit breakage due to kernel regressionRich Felker2015-06-201-0/+1
| | | | | | | | | linux kernel commit 46e12c07b3b9603c60fc1d421ff18618241cb081 caused the mips syscall mechanism to fail with EFAULT when the userspace stack pointer is invalid, breaking __unmapself used for detached thread exit. the workaround is to set $sp to a known-valid, readable address, and the simplest one to obtain is the address of the current function, which is available (per o32 calling convention) in $25.
* ignore ENOSYS error from mprotect in pthread_create and dynamic linkerRich Felker2015-06-172-3/+6
| | | | | this error simply indicated a system without memory protection (NOMMU) and should not cause failure in the caller.
* switch to using trap number 31 for syscalls on shRich Felker2015-06-167-10/+10
| | | | | | | | | | | | | | | | | | | nominally the low bits of the trap number on sh are the number of syscall arguments, but they have never been used by the kernel, and some code making syscalls does not even know the number of arguments and needs to pass an arbitrary high number anyway. sh3/sh4 traditionally used the trap range 16-31 for syscalls, but part of this range overlapped with hardware exceptions/interrupts on sh2 hardware, so an incompatible range 32-47 was chosen for sh2. using trap number 31 everywhere, since it's in the existing sh3/sh4 range and does not conflict with sh2 hardware, is a proposed unification of the kernel syscall convention that will allow binaries to be shared between sh2 and sh3/sh4. if this is not accepted into the kernel, we can refit the sh2 target with runtime selection mechanisms for the trap number, but doing so would be invasive and would entail non-trivial overhead.
* switch sh port's __unmapself to generic version when running on sh2/nommuRich Felker2015-06-161-3/+3
| | | | | | | | | | | | | due to the way the interrupt and syscall trap mechanism works, userspace on sh2 must never set the stack pointer to an invalid value. thus, the approach used on most archs, where __unmapself executes with no stack for the interval between SYS_munmap and SYS_exit, is not viable on sh2. in order not to pessimize sh3/sh4, the sh asm version of __unmapself is not removed. instead it's renamed and redirected through code that calls either the generic (safe) __unmapself or the sh3/sh4 asm, depending on compile-time and run-time conditions.
* add support for sh2 interrupt-masking-based atomics to sh portRich Felker2015-06-161-6/+0
| | | | | | | | | | | | | | | | | | | the sh2 target is being considered an ISA subset of sh3/sh4, in the sense that binaries built for sh2 are intended to be usable on later cpu models/kernels with mmu support. so rather than hard-coding sh2-specific atomics, the runtime atomic selection mechanisms that was already in place has been extended to add sh2 atomics. at this time, the sh2 atomics are not SMP-compatible; since the ISA lacks actual atomic operations, the new code instead masks interrupts for the duration of the atomic operation, producing an atomic result on single-core. this is only possible because the kernel/hardware does not impose protections against userspace doing so. additional changes will be needed to support future SMP systems. care has been taken to avoid producing significant additional code size in the case where it's known at compile-time that the target is not sh2 and does not need sh2-specific code.
* refactor stdio open file list handling, move it out of global libc structRich Felker2015-06-1612-41/+42
| | | | | | | | | | | | | functions which open in-memory FILE stream variants all shared a tail with __fdopen, adding the FILE structure to stdio's open file list. replacing this common tail with a function call reduces code size and duplication of logic. the list is also partially encapsulated now. function signatures were chosen to facilitate tail call optimization and reduce the need for additional accessor functions. with these changes, static linked programs that do not use stdio no longer have an open file list at all.
* byte-based C locale, phase 3: make MB_CUR_MAX variable to activate codeRich Felker2015-06-161-0/+3
| | | | | | | | this patch activates the new byte-based C locale (high bytes treated as abstract code unit "characters" rather than decoded as multibyte characters) by making the value of MB_CUR_MAX depend on the active locale. for the C locale, the LC_CTYPE category pointer is null, yielding a value of 1. all other locales yield a value of 4.
* byte-based C locale, phase 2: stdio and iconv (multibyte callers)Rich Felker2015-06-167-8/+40
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | this patch adjusts libc components which use the multibyte functions internally, and which depend on them operating in a particular encoding, to make the appropriate locale changes before calling them and restore the calling thread's locale afterwards. activating the byte-based C locale without these changes would cause regressions in stdio and iconv. in the case of iconv, the current implementation was simply using the multibyte functions as UTF-8 conversions. setting a multibyte UTF-8 locale for the duration of the iconv operation allows the code to continue working. in the case of stdio, POSIX requires that FILE streams have an encoding rule bound at the time of setting wide orientation. as long as all locales, including the C locale, used the same encoding, treating high bytes as UTF-8, there was no need to store an encoding rule as part of the stream's state. a new locale field in the FILE structure points to the locale that should be made active during fgetwc/fputwc/ungetwc on the stream. it cannot point to the locale active at the time the stream becomes oriented, because this locale could be mutable (the global locale) or could be destroyed (locale_t objects produced by newlocale) before the stream is closed. instead, a pointer to the static C or C.UTF-8 locale object added in commit commit aeeac9ca5490d7d90fe061ab72da446c01ddf746 is used. this is valid since categories other than LC_CTYPE will not affect these functions.
* byte-based C locale, phase 1: multibyte character handling functionsRich Felker2015-06-1610-7/+53
| | | | | | | | | | | | | | | | | | this patch makes the functions which work directly on multibyte characters treat the high bytes as individual abstract code units rather than as multibyte sequences when MB_CUR_MAX is 1. since MB_CUR_MAX is presently defined as a constant 4, all of the new code added is dead code, and optimizing compilers' code generation should not be affected at all. a future commit will activate the new code. as abstract code units, bytes 0x80 to 0xff are represented by wchar_t values 0xdf80 to 0xdfff, at the end of the surrogates range. this ensures that they will never be misinterpreted as Unicode characters, and that all wctype functions return false for these "characters" without needing locale-specific logic. a high range outside of Unicode such as 0x7fffff80 to 0x7fffffff was also considered, but since C11's char16_t also needs to be able to represent conversions of these bytes, the surrogate range was the natural choice.
* fix btowc corner caseRich Felker2015-06-161-0/+1
| | | | | | | btowc is required to interpret its argument by conversion to unsigned char, unless the argument is equal to EOF. since the conversion to produces a non-character value anyway, we can just unconditionally convert, for now.
* refactor malloc's expand_heap to share with __simple_mallocRich Felker2015-06-143-81/+126
| | | | | | | | | | | | | | | | | | | this extends the brk/stack collision protection added to full malloc in commit 276904c2f6bde3a31a24ebfa201482601d18b4f9 to also protect the __simple_malloc function used in static-linked programs that don't reference the free function. it also extends support for using mmap when brk fails, which full malloc got in commit 5446303328adf4b4e36d9fba21848e6feb55fab4, to __simple_malloc. since __simple_malloc may expand the heap by arbitrarily large increments, the stack collision detection is enhanced to detect interval overlap rather than just proximity of a single address to the stack. code size is increased a bit, but this is partly offset by the sharing of code between the two malloc implementations, which due to linking semantics, both get linked in a program that needs the full malloc with realloc/free support.
* remove cancellation points in stdioRich Felker2015-06-133-24/+3
| | | | | | | | | | | | | | | | commit 58165923890865a6ac042fafce13f440ee986fd9 added these optional cancellation points on the basis that cancellable stdio could be useful, to unblock threads stuck on stdio operations that will never complete. however, the only way to ensure that cancellation can achieve this is to violate the rules for side effects when cancellation is acted upon, discarding knowledge of any partial data transfer already completed. our implementation exhibited this behavior and was thus non-conforming. in addition to improving correctness, removing these cancellation points moderately reduces code size, and should significantly improve performance on i386, where sysenter/syscall instructions can be used instead of "int $128" for non-cancellable syscalls.