/* Library support for -fsplit-stack. */ /* Copyright (C) 2009-2014 Free Software Foundation, Inc. Contributed by Ian Lance Taylor . This file is part of GCC. GCC is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version. GCC is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. Under Section 7 of GPL version 3, you are granted additional permissions described in the GCC Runtime Library Exception, version 3.1, as published by the Free Software Foundation. You should have received a copy of the GNU General Public License and a copy of the GCC Runtime Library Exception along with this program; see the files COPYING3 and COPYING.RUNTIME respectively. If not, see . */ #include "tconfig.h" #include "tsystem.h" #include "coretypes.h" #include "tm.h" #include "libgcc_tm.h" /* If inhibit_libc is defined, we can not compile this file. The effect is that people will not be able to use -fsplit-stack. That is much better than failing the build particularly since people will want to define inhibit_libc while building a compiler which can build glibc. */ #ifndef inhibit_libc #include #include #include #include #include #include #include #include #include "generic-morestack.h" typedef unsigned uintptr_type __attribute__ ((mode (pointer))); /* This file contains subroutines that are used by code compiled with -fsplit-stack. */ /* Declare functions to avoid warnings--there is no header file for these internal functions. We give most of these functions the flatten attribute in order to minimize their stack usage--here we must minimize stack usage even at the cost of code size, and in general inlining everything will do that. */ extern void __generic_morestack_set_initial_sp (void *sp, size_t len) __attribute__ ((no_split_stack, flatten, visibility ("hidden"))); extern void * __generic_morestack (size_t *frame_size, void *old_stack, size_t param_size) __attribute__ ((no_split_stack, flatten, visibility ("hidden"))); extern void * __generic_releasestack (size_t *pavailable) __attribute__ ((no_split_stack, flatten, visibility ("hidden"))); extern void __morestack_block_signals (void) __attribute__ ((no_split_stack, flatten, visibility ("hidden"))); extern void __morestack_unblock_signals (void) __attribute__ ((no_split_stack, flatten, visibility ("hidden"))); extern size_t __generic_findstack (void *stack) __attribute__ ((no_split_stack, flatten, visibility ("hidden"))); extern void __morestack_load_mmap (void) __attribute__ ((no_split_stack, visibility ("hidden"))); extern void * __morestack_allocate_stack_space (size_t size) __attribute__ ((visibility ("hidden"))); /* These are functions which -fsplit-stack code can call. These are not called by the compiler, and are not hidden. FIXME: These should be in some header file somewhere, somehow. */ extern void * __splitstack_find (void *, void *, size_t *, void **, void **, void **) __attribute__ ((visibility ("default"))); extern void __splitstack_block_signals (int *, int *) __attribute__ ((visibility ("default"))); extern void __splitstack_getcontext (void *context[10]) __attribute__ ((no_split_stack, visibility ("default"))); extern void __splitstack_setcontext (void *context[10]) __attribute__ ((no_split_stack, visibility ("default"))); extern void * __splitstack_makecontext (size_t, void *context[10], size_t *) __attribute__ ((visibility ("default"))); extern void * __splitstack_resetcontext (void *context[10], size_t *) __attribute__ ((visibility ("default"))); extern void __splitstack_releasecontext (void *context[10]) __attribute__ ((visibility ("default"))); extern void __splitstack_block_signals_context (void *context[10], int *, int *) __attribute__ ((visibility ("default"))); extern void * __splitstack_find_context (void *context[10], size_t *, void **, void **, void **) __attribute__ ((visibility ("default"))); /* These functions must be defined by the processor specific code. */ extern void *__morestack_get_guard (void) __attribute__ ((no_split_stack, visibility ("hidden"))); extern void __morestack_set_guard (void *) __attribute__ ((no_split_stack, visibility ("hidden"))); extern void *__morestack_make_guard (void *, size_t) __attribute__ ((no_split_stack, visibility ("hidden"))); /* When we allocate a stack segment we put this header at the start. */ struct stack_segment { /* The previous stack segment--when a function running on this stack segment returns, it will run on the previous one. */ struct stack_segment *prev; /* The next stack segment, if it has been allocated--when a function is running on this stack segment, the next one is not being used. */ struct stack_segment *next; /* The total size of this stack segment. */ size_t size; /* The stack address when this stack was created. This is used when popping the stack. */ void *old_stack; /* A list of memory blocks allocated by dynamic stack allocation. */ struct dynamic_allocation_blocks *dynamic_allocation; /* A list of dynamic memory blocks no longer needed. */ struct dynamic_allocation_blocks *free_dynamic_allocation; /* An extra pointer in case we need some more information some day. */ void *extra; }; /* This structure holds the (approximate) initial stack pointer and size for the system supplied stack for a thread. This is set when the thread is created. We also store a sigset_t here to hold the signal mask while splitting the stack, since we don't want to store that on the stack. */ struct initial_sp { /* The initial stack pointer. */ void *sp; /* The stack length. */ size_t len; /* A signal mask, put here so that the thread can use it without needing stack space. */ sigset_t mask; /* Non-zero if we should not block signals. This is a reversed flag so that the default zero value is the safe value. The type is uintptr_type because it replaced one of the void * pointers in extra. */ uintptr_type dont_block_signals; /* Some extra space for later extensibility. */ void *extra[4]; }; /* A list of memory blocks allocated by dynamic stack allocation. This is used for code that calls alloca or uses variably sized arrays. */ struct dynamic_allocation_blocks { /* The next block in the list. */ struct dynamic_allocation_blocks *next; /* The size of the allocated memory. */ size_t size; /* The allocated memory. */ void *block; }; /* These thread local global variables must be shared by all split stack code across shared library boundaries. Therefore, they have default visibility. They have extensibility fields if needed for new versions. If more radical changes are needed, new code can be written using new variable names, while still using the existing variables in a backward compatible manner. Symbol versioning is also used, although, since these variables are only referenced by code in this file and generic-morestack-thread.c, it is likely that simply using new names will suffice. */ /* The first stack segment allocated for this thread. */ __thread struct stack_segment *__morestack_segments __attribute__ ((visibility ("default"))); /* The stack segment that we think we are currently using. This will be correct in normal usage, but will be incorrect if an exception unwinds into a different stack segment or if longjmp jumps to a different stack segment. */ __thread struct stack_segment *__morestack_current_segment __attribute__ ((visibility ("default"))); /* The initial stack pointer and size for this thread. */ __thread struct initial_sp __morestack_initial_sp __attribute__ ((visibility ("default"))); /* A static signal mask, to avoid taking up stack space. */ static sigset_t __morestack_fullmask; /* Convert an integer to a decimal string without using much stack space. Return a pointer to the part of the buffer to use. We this instead of sprintf because sprintf will require too much stack space. */ static char * print_int (int val, char *buf, int buflen, size_t *print_len) { int is_negative; int i; unsigned int uval; uval = (unsigned int) val; if (val >= 0) is_negative = 0; else { is_negative = 1; uval = - uval; } i = buflen; do { --i; buf[i] = '0' + (uval % 10); uval /= 10; } while (uval != 0 && i > 0); if (is_negative) { if (i > 0) --i; buf[i] = '-'; } *print_len = buflen - i; return buf + i; } /* Print the string MSG/LEN, the errno number ERR, and a newline on stderr. Then crash. */ void __morestack_fail (const char *, size_t, int) __attribute__ ((noreturn)); void __morestack_fail (const char *msg, size_t len, int err) { char buf[24]; static const char nl[] = "\n"; struct iovec iov[3]; union { char *p; const char *cp; } const_cast; const_cast.cp = msg; iov[0].iov_base = const_cast.p; iov[0].iov_len = len; /* We can't call strerror, because it may try to translate the error message, and that would use too much stack space. */ iov[1].iov_base = print_int (err, buf, sizeof buf, &iov[1].iov_len); const_cast.cp = &nl[0]; iov[2].iov_base = const_cast.p; iov[2].iov_len = sizeof nl - 1; /* FIXME: On systems without writev we need to issue three write calls, or punt on printing errno. For now this is irrelevant since stack splitting only works on GNU/Linux anyhow. */ writev (2, iov, 3); abort (); } /* Allocate a new stack segment. FRAME_SIZE is the required frame size. */ static struct stack_segment * allocate_segment (size_t frame_size) { static unsigned int static_pagesize; static int use_guard_page; unsigned int pagesize; unsigned int overhead; unsigned int allocate; void *space; struct stack_segment *pss; pagesize = static_pagesize; if (pagesize == 0) { unsigned int p; pagesize = getpagesize (); #ifdef __GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 p = __sync_val_compare_and_swap (&static_pagesize, 0, pagesize); #else /* Just hope this assignment is atomic. */ static_pagesize = pagesize; p = 0; #endif use_guard_page = getenv ("SPLIT_STACK_GUARD") != 0; /* FIXME: I'm not sure this assert should be in the released code. */ assert (p == 0 || p == pagesize); } overhead = sizeof (struct stack_segment); allocate = pagesize; if (allocate < MINSIGSTKSZ) allocate = ((MINSIGSTKSZ + overhead + pagesize - 1) & ~ (pagesize - 1)); if (allocate < frame_size) allocate = ((frame_size + overhead + pagesize - 1) & ~ (pagesize - 1)); if (use_guard_page) allocate += pagesize; /* FIXME: If this binary requires an executable stack, then we need to set PROT_EXEC. Unfortunately figuring that out is complicated and target dependent. We would need to use dl_iterate_phdr to see if there is any object which does not have a PT_GNU_STACK phdr, though only for architectures which use that mechanism. */ space = mmap (NULL, allocate, PROT_READ | PROT_WRITE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0); if (space == MAP_FAILED) { static const char msg[] = "unable to allocate additional stack space: errno "; __morestack_fail (msg, sizeof msg - 1, errno); } if (use_guard_page) { void *guard; #ifdef __LIBGCC_STACK_GROWS_DOWNWARD__ guard = space; space = (char *) space + pagesize; #else guard = space + allocate - pagesize; #endif mprotect (guard, pagesize, PROT_NONE); allocate -= pagesize; } pss = (struct stack_segment *) space; pss->prev = NULL; pss->next = NULL; pss->size = allocate - overhead; pss->dynamic_allocation = NULL; pss->free_dynamic_allocation = NULL; pss->extra = NULL; return pss; } /* Free a list of dynamic blocks. */ static void free_dynamic_blocks (struct dynamic_allocation_blocks *p) { while (p != NULL) { struct dynamic_allocation_blocks *next; next = p->next; free (p->block); free (p); p = next; } } /* Merge two lists of dynamic blocks. */ static struct dynamic_allocation_blocks * merge_dynamic_blocks (struct dynamic_allocation_blocks *a, struct dynamic_allocation_blocks *b) { struct dynamic_allocation_blocks **pp; if (a == NULL) return b; if (b == NULL) return a; for (pp = &a->next; *pp != NULL; pp = &(*pp)->next) ; *pp = b; return a; } /* Release stack segments. If FREE_DYNAMIC is non-zero, we also free any dynamic blocks. Otherwise we return them. */ struct dynamic_allocation_blocks * __morestack_release_segments (struct stack_segment **pp, int free_dynamic) { struct dynamic_allocation_blocks *ret; struct stack_segment *pss; ret = NULL; pss = *pp; while (pss != NULL) { struct stack_segment *next; unsigned int allocate; next = pss->next; if (pss->dynamic_allocation != NULL || pss->free_dynamic_allocation != NULL) { if (free_dynamic) { free_dynamic_blocks (pss->dynamic_allocation); free_dynamic_blocks (pss->free_dynamic_allocation); } else { ret = merge_dynamic_blocks (pss->dynamic_allocation, ret); ret = merge_dynamic_blocks (pss->free_dynamic_allocation, ret); } } allocate = pss->size + sizeof (struct stack_segment); if (munmap (pss, allocate) < 0) { static const char msg[] = "munmap of stack space failed: errno "; __morestack_fail (msg, sizeof msg - 1, errno); } pss = next; } *pp = NULL; return ret; } /* This function is called by a processor specific function to set the initial stack pointer for a thread. The operating system will always create a stack for a thread. Here we record a stack pointer near the base of that stack. The size argument lets the processor specific code estimate how much stack space is available on this initial stack. */ void __generic_morestack_set_initial_sp (void *sp, size_t len) { /* The stack pointer most likely starts on a page boundary. Adjust to the nearest 512 byte boundary. It's not essential that we be precise here; getting it wrong will just leave some stack space unused. */ #ifdef __LIBGCC_STACK_GROWS_DOWNWARD__ sp = (void *) ((((__UINTPTR_TYPE__) sp + 511U) / 512U) * 512U); #else sp = (void *) ((((__UINTPTR_TYPE__) sp - 511U) / 512U) * 512U); #endif __morestack_initial_sp.sp = sp; __morestack_initial_sp.len = len; sigemptyset (&__morestack_initial_sp.mask); sigfillset (&__morestack_fullmask); #if defined(__GLIBC__) && defined(__linux__) /* In glibc, the first two real time signals are used by the NPTL threading library. By taking them out of the set of signals, we avoiding copying the signal mask in pthread_sigmask. More importantly, pthread_sigmask uses less stack space on x86_64. */ sigdelset (&__morestack_fullmask, __SIGRTMIN); sigdelset (&__morestack_fullmask, __SIGRTMIN + 1); #endif } /* This function is called by a processor specific function which is run in the prologue when more stack is needed. The processor specific function handles the details of saving registers and frobbing the actual stack pointer. This function is responsible for allocating a new stack segment and for copying a parameter block from the old stack to the new one. On function entry *PFRAME_SIZE is the size of the required stack frame--the returned stack must be at least this large. On function exit *PFRAME_SIZE is the amount of space remaining on the allocated stack. OLD_STACK points at the parameters the old stack (really the current one while this function is running). OLD_STACK is saved so that it can be returned by a later call to __generic_releasestack. PARAM_SIZE is the size in bytes of parameters to copy to the new stack. This function returns a pointer to the new stack segment, pointing to the memory after the parameters have been copied. The returned value minus the returned *PFRAME_SIZE (or plus if the stack grows upward) is the first address on the stack which should not be used. This function is running on the old stack and has only a limited amount of stack space available. */ void * __generic_morestack (size_t *pframe_size, void *old_stack, size_t param_size) { size_t frame_size = *pframe_size; struct stack_segment *current; struct stack_segment **pp; struct dynamic_allocation_blocks *dynamic; char *from; char *to; void *ret; size_t i; size_t aligned; current = __morestack_current_segment; pp = current != NULL ? ¤t->next : &__morestack_segments; if (*pp != NULL && (*pp)->size < frame_size) dynamic = __morestack_release_segments (pp, 0); else dynamic = NULL; current = *pp; if (current == NULL) { current = allocate_segment (frame_size + param_size); current->prev = __morestack_current_segment; *pp = current; } current->old_stack = old_stack; __morestack_current_segment = current; if (dynamic != NULL) { /* Move the free blocks onto our list. We don't want to call free here, as we are short on stack space. */ current->free_dynamic_allocation = merge_dynamic_blocks (dynamic, current->free_dynamic_allocation); } *pframe_size = current->size - param_size; /* Align the returned stack to a 32-byte boundary. */ aligned = (param_size + 31) & ~ (size_t) 31; #ifdef __LIBGCC_STACK_GROWS_DOWNWARD__ { char *bottom = (char *) (current + 1) + current->size; to = bottom - aligned; ret = bottom - aligned; } #else to = current + 1; to += aligned - param_size; ret = (char *) (current + 1) + aligned; #endif /* We don't call memcpy to avoid worrying about the dynamic linker trying to resolve it. */ from = (char *) old_stack; for (i = 0; i < param_size; i++) *to++ = *from++; return ret; } /* This function is called by a processor specific function when it is ready to release a stack segment. We don't actually release the stack segment, we just move back to the previous one. The current stack segment will still be available if we need it in __generic_morestack. This returns a pointer to the new stack segment to use, which is the one saved by a previous call to __generic_morestack. The processor specific function is then responsible for actually updating the stack pointer. This sets *PAVAILABLE to the amount of stack space now available. */ void * __generic_releasestack (size_t *pavailable) { struct stack_segment *current; void *old_stack; current = __morestack_current_segment; old_stack = current->old_stack; current = current->prev; __morestack_current_segment = current; if (current != NULL) { #ifdef __LIBGCC_STACK_GROWS_DOWNWARD__ *pavailable = (char *) old_stack - (char *) (current + 1); #else *pavailable = (char *) (current + 1) + current->size - (char *) old_stack; #endif } else { size_t used; /* We have popped back to the original stack. */ #ifdef __LIBGCC_STACK_GROWS_DOWNWARD__ if ((char *) old_stack >= (char *) __morestack_initial_sp.sp) used = 0; else used = (char *) __morestack_initial_sp.sp - (char *) old_stack; #else if ((char *) old_stack <= (char *) __morestack_initial_sp.sp) used = 0; else used = (char *) old_stack - (char *) __morestack_initial_sp.sp; #endif if (used > __morestack_initial_sp.len) *pavailable = 0; else *pavailable = __morestack_initial_sp.len - used; } return old_stack; } /* Block signals while splitting the stack. This avoids trouble if we try to invoke a signal handler which itself wants to split the stack. */ extern int pthread_sigmask (int, const sigset_t *, sigset_t *) __attribute__ ((weak)); void __morestack_block_signals (void) { if (__morestack_initial_sp.dont_block_signals) ; else if (pthread_sigmask) pthread_sigmask (SIG_BLOCK, &__morestack_fullmask, &__morestack_initial_sp.mask); else sigprocmask (SIG_BLOCK, &__morestack_fullmask, &__morestack_initial_sp.mask); } /* Unblock signals while splitting the stack. */ void __morestack_unblock_signals (void) { if (__morestack_initial_sp.dont_block_signals) ; else if (pthread_sigmask) pthread_sigmask (SIG_SETMASK, &__morestack_initial_sp.mask, NULL); else sigprocmask (SIG_SETMASK, &__morestack_initial_sp.mask, NULL); } /* This function is called to allocate dynamic stack space, for alloca or a variably sized array. This is a regular function with sufficient stack space, so we just use malloc to allocate the space. We attach the allocated blocks to the current stack segment, so that they will eventually be reused or freed. */ void * __morestack_allocate_stack_space (size_t size) { struct stack_segment *seg, *current; struct dynamic_allocation_blocks *p; /* We have to block signals to avoid getting confused if we get interrupted by a signal whose handler itself uses alloca or a variably sized array. */ __morestack_block_signals (); /* Since we don't want to call free while we are low on stack space, we may have a list of already allocated blocks waiting to be freed. Release them all, unless we find one that is large enough. We don't look at every block to see if one is large enough, just the first one, because we aren't trying to build a memory allocator here, we're just trying to speed up common cases. */ current = __morestack_current_segment; p = NULL; for (seg = __morestack_segments; seg != NULL; seg = seg->next) { p = seg->free_dynamic_allocation; if (p != NULL) { if (p->size >= size) { seg->free_dynamic_allocation = p->next; break; } free_dynamic_blocks (p); seg->free_dynamic_allocation = NULL; p = NULL; } } if (p == NULL) { /* We need to allocate additional memory. */ p = malloc (sizeof (*p)); if (p == NULL) abort (); p->size = size; p->block = malloc (size); if (p->block == NULL) abort (); } /* If we are still on the initial stack, then we have a space leak. FIXME. */ if (current != NULL) { p->next = current->dynamic_allocation; current->dynamic_allocation = p; } __morestack_unblock_signals (); return p->block; } /* Find the stack segment for STACK and return the amount of space available. This is used when unwinding the stack because of an exception, in order to reset the stack guard correctly. */ size_t __generic_findstack (void *stack) { struct stack_segment *pss; size_t used; for (pss = __morestack_current_segment; pss != NULL; pss = pss->prev) { if ((char *) pss < (char *) stack && (char *) pss + pss->size > (char *) stack) { __morestack_current_segment = pss; #ifdef __LIBGCC_STACK_GROWS_DOWNWARD__ return (char *) stack - (char *) (pss + 1); #else return (char *) (pss + 1) + pss->size - (char *) stack; #endif } } /* We have popped back to the original stack. */ if (__morestack_initial_sp.sp == NULL) return 0; #ifdef __LIBGCC_STACK_GROWS_DOWNWARD__ if ((char *) stack >= (char *) __morestack_initial_sp.sp) used = 0; else used = (char *) __morestack_initial_sp.sp - (char *) stack; #else if ((char *) stack <= (char *) __morestack_initial_sp.sp) used = 0; else used = (char *) stack - (char *) __morestack_initial_sp.sp; #endif if (used > __morestack_initial_sp.len) return 0; else return __morestack_initial_sp.len - used; } /* This function is called at program startup time to make sure that mmap, munmap, and getpagesize are resolved if linking dynamically. We want to resolve them while we have enough stack for them, rather than calling into the dynamic linker while low on stack space. */ void __morestack_load_mmap (void) { /* Call with bogus values to run faster. We don't care if the call fails. Pass __MORESTACK_CURRENT_SEGMENT to make sure that any TLS accessor function is resolved. */ mmap (__morestack_current_segment, 0, PROT_READ, MAP_ANONYMOUS, -1, 0); mprotect (NULL, 0, 0); munmap (0, getpagesize ()); } /* This function may be used to iterate over the stack segments. This can be called like this. void *next_segment = NULL; void *next_sp = NULL; void *initial_sp = NULL; void *stack; size_t stack_size; while ((stack = __splitstack_find (next_segment, next_sp, &stack_size, &next_segment, &next_sp, &initial_sp)) != NULL) { // Stack segment starts at stack and is stack_size bytes long. } There is no way to iterate over the stack segments of a different thread. However, what is permitted is for one thread to call this with the first two values NULL, to pass next_segment, next_sp, and initial_sp to a different thread, and then to suspend one way or another. A different thread may run the subsequent __morestack_find iterations. Of course, this will only work if the first thread is suspended during the __morestack_find iterations. If not, the second thread will be looking at the stack while it is changing, and anything could happen. FIXME: This should be declared in some header file, but where? */ void * __splitstack_find (void *segment_arg, void *sp, size_t *len, void **next_segment, void **next_sp, void **initial_sp) { struct stack_segment *segment; void *ret; char *nsp; if (segment_arg == (void *) (uintptr_type) 1) { char *isp = (char *) *initial_sp; if (isp == NULL) return NULL; *next_segment = (void *) (uintptr_type) 2; *next_sp = NULL; #ifdef __LIBGCC_STACK_GROWS_DOWNWARD__ if ((char *) sp >= isp) return NULL; *len = (char *) isp - (char *) sp; return sp; #else if ((char *) sp <= (char *) isp) return NULL; *len = (char *) sp - (char *) isp; return (void *) isp; #endif } else if (segment_arg == (void *) (uintptr_type) 2) return NULL; else if (segment_arg != NULL) segment = (struct stack_segment *) segment_arg; else { *initial_sp = __morestack_initial_sp.sp; segment = __morestack_current_segment; sp = (void *) &segment; while (1) { if (segment == NULL) return __splitstack_find ((void *) (uintptr_type) 1, sp, len, next_segment, next_sp, initial_sp); if ((char *) sp >= (char *) (segment + 1) && (char *) sp <= (char *) (segment + 1) + segment->size) break; segment = segment->prev; } } if (segment->prev == NULL) *next_segment = (void *) (uintptr_type) 1; else *next_segment = segment->prev; /* The old_stack value is the address of the function parameters of the function which called __morestack. So if f1 called f2 which called __morestack, the stack looks like this: parameters <- old_stack return in f1 return in f2 registers pushed by __morestack The registers pushed by __morestack may not be visible on any other stack, if we are being called by a signal handler immediately after the call to __morestack_unblock_signals. We want to adjust our return value to include those registers. This is target dependent. */ nsp = (char *) segment->old_stack; if (nsp == NULL) { /* We've reached the top of the stack. */ *next_segment = (void *) (uintptr_type) 2; } else { #if defined (__x86_64__) nsp -= 12 * sizeof (void *); #elif defined (__i386__) nsp -= 6 * sizeof (void *); #else #error "unrecognized target" #endif *next_sp = (void *) nsp; } #ifdef __LIBGCC_STACK_GROWS_DOWNWARD__ *len = (char *) (segment + 1) + segment->size - (char *) sp; ret = (void *) sp; #else *len = (char *) sp - (char *) (segment + 1); ret = (void *) (segment + 1); #endif return ret; } /* Tell the split stack code whether it has to block signals while manipulating the stack. This is for programs in which some threads block all signals. If a thread already blocks signals, there is no need for the split stack code to block them as well. If NEW is not NULL, then if *NEW is non-zero signals will be blocked while splitting the stack, otherwise they will not. If OLD is not NULL, *OLD will be set to the old value. */ void __splitstack_block_signals (int *new, int *old) { if (old != NULL) *old = __morestack_initial_sp.dont_block_signals ? 0 : 1; if (new != NULL) __morestack_initial_sp.dont_block_signals = *new ? 0 : 1; } /* The offsets into the arrays used by __splitstack_getcontext and __splitstack_setcontext. */ enum __splitstack_context_offsets { MORESTACK_SEGMENTS = 0, CURRENT_SEGMENT = 1, CURRENT_STACK = 2, STACK_GUARD = 3, INITIAL_SP = 4, INITIAL_SP_LEN = 5, BLOCK_SIGNALS = 6, NUMBER_OFFSETS = 10 }; /* Get the current split stack context. This may be used for coroutine switching, similar to getcontext. The argument should have at least 10 void *pointers for extensibility, although we don't currently use all of them. This would normally be called immediately before a call to getcontext or swapcontext or setjmp. */ void __splitstack_getcontext (void *context[NUMBER_OFFSETS]) { memset (context, 0, NUMBER_OFFSETS * sizeof (void *)); context[MORESTACK_SEGMENTS] = (void *) __morestack_segments; context[CURRENT_SEGMENT] = (void *) __morestack_current_segment; context[CURRENT_STACK] = (void *) &context; context[STACK_GUARD] = __morestack_get_guard (); context[INITIAL_SP] = (void *) __morestack_initial_sp.sp; context[INITIAL_SP_LEN] = (void *) (uintptr_type) __morestack_initial_sp.len; context[BLOCK_SIGNALS] = (void *) __morestack_initial_sp.dont_block_signals; } /* Set the current split stack context. The argument should be a context previously passed to __splitstack_getcontext. This would normally be called immediately after a call to getcontext or swapcontext or setjmp if something jumped to it. */ void __splitstack_setcontext (void *context[NUMBER_OFFSETS]) { __morestack_segments = (struct stack_segment *) context[MORESTACK_SEGMENTS]; __morestack_current_segment = (struct stack_segment *) context[CURRENT_SEGMENT]; __morestack_set_guard (context[STACK_GUARD]); __morestack_initial_sp.sp = context[INITIAL_SP]; __morestack_initial_sp.len = (size_t) context[INITIAL_SP_LEN]; __morestack_initial_sp.dont_block_signals = (uintptr_type) context[BLOCK_SIGNALS]; } /* Create a new split stack context. This will allocate a new stack segment which may be used by a coroutine. STACK_SIZE is the minimum size of the new stack. The caller is responsible for actually setting the stack pointer. This would normally be called before a call to makecontext, and the returned stack pointer and size would be used to set the uc_stack field. A function called via makecontext on a stack created by __splitstack_makecontext may not return. Note that the returned pointer points to the lowest address in the stack space, and thus may not be the value to which to set the stack pointer. */ void * __splitstack_makecontext (size_t stack_size, void *context[NUMBER_OFFSETS], size_t *size) { struct stack_segment *segment; void *initial_sp; memset (context, 0, NUMBER_OFFSETS * sizeof (void *)); segment = allocate_segment (stack_size); context[MORESTACK_SEGMENTS] = segment; context[CURRENT_SEGMENT] = segment; #ifdef __LIBGCC_STACK_GROWS_DOWNWARD__ initial_sp = (void *) ((char *) (segment + 1) + segment->size); #else initial_sp = (void *) (segment + 1); #endif context[STACK_GUARD] = __morestack_make_guard (initial_sp, segment->size); context[INITIAL_SP] = NULL; context[INITIAL_SP_LEN] = 0; *size = segment->size; return (void *) (segment + 1); } /* Given an existing split stack context, reset it back to the start of the stack. Return the stack pointer and size, appropriate for use with makecontext. This may be used if a coroutine exits, in order to reuse the stack segments for a new coroutine. */ void * __splitstack_resetcontext (void *context[10], size_t *size) { struct stack_segment *segment; void *initial_sp; size_t initial_size; void *ret; /* Reset the context assuming that MORESTACK_SEGMENTS, INITIAL_SP and INITIAL_SP_LEN are correct. */ segment = context[MORESTACK_SEGMENTS]; context[CURRENT_SEGMENT] = segment; context[CURRENT_STACK] = NULL; if (segment == NULL) { initial_sp = context[INITIAL_SP]; initial_size = (uintptr_type) context[INITIAL_SP_LEN]; ret = initial_sp; #ifdef __LIBGCC_STACK_GROWS_DOWNWARD__ ret = (void *) ((char *) ret - initial_size); #endif } else { #ifdef __LIBGCC_STACK_GROWS_DOWNWARD__ initial_sp = (void *) ((char *) (segment + 1) + segment->size); #else initial_sp = (void *) (segment + 1); #endif initial_size = segment->size; ret = (void *) (segment + 1); } context[STACK_GUARD] = __morestack_make_guard (initial_sp, initial_size); context[BLOCK_SIGNALS] = NULL; *size = initial_size; return ret; } /* Release all the memory associated with a splitstack context. This may be used if a coroutine exits and the associated stack should be freed. */ void __splitstack_releasecontext (void *context[10]) { __morestack_release_segments (((struct stack_segment **) &context[MORESTACK_SEGMENTS]), 1); } /* Like __splitstack_block_signals, but operating on CONTEXT, rather than on the current state. */ void __splitstack_block_signals_context (void *context[NUMBER_OFFSETS], int *new, int *old) { if (old != NULL) *old = ((uintptr_type) context[BLOCK_SIGNALS]) != 0 ? 0 : 1; if (new != NULL) context[BLOCK_SIGNALS] = (void *) (uintptr_type) (*new ? 0 : 1); } /* Find the stack segments associated with a split stack context. This will return the address of the first stack segment and set *STACK_SIZE to its size. It will set next_segment, next_sp, and initial_sp which may be passed to __splitstack_find to find the remaining segments. */ void * __splitstack_find_context (void *context[NUMBER_OFFSETS], size_t *stack_size, void **next_segment, void **next_sp, void **initial_sp) { void *sp; struct stack_segment *segment; *initial_sp = context[INITIAL_SP]; sp = context[CURRENT_STACK]; if (sp == NULL) { /* Most likely this context was created but was never used. The value 2 is a code used by __splitstack_find to mean that we have reached the end of the list of stacks. */ *next_segment = (void *) (uintptr_type) 2; *next_sp = NULL; *initial_sp = NULL; return NULL; } segment = context[CURRENT_SEGMENT]; if (segment == NULL) { /* Most likely this context was saved by a thread which was not created using __splistack_makecontext and which has never split the stack. The value 1 is a code used by __splitstack_find to look at the initial stack. */ segment = (struct stack_segment *) (uintptr_type) 1; } return __splitstack_find (segment, sp, stack_size, next_segment, next_sp, initial_sp); } #endif /* !defined (inhibit_libc) */