/* Library support for -fsplit-stack. */
/* Copyright (C) 2009-2020 Free Software Foundation, Inc.
Contributed by Ian Lance Taylor <iant@google.com>.
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
<http://www.gnu.org/licenses/>. */
#pragma GCC optimize ("no-isolate-erroneous-paths-dereference")
/* powerpc 32-bit not supported. */
#if !defined __powerpc__ || defined __powerpc64__
#include "tconfig.h"
#include "tsystem.h"
#include "coretypes.h"
#include "tm.h"
#include "libgcc_tm.h"
/* If inhibit_libc is defined, we cannot 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 <assert.h>
#include <errno.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/uio.h>
#include "generic-morestack.h"
/* Some systems use LD_PRELOAD or similar tricks to add hooks to
mmap/munmap. That breaks this code, because when we call mmap
there is enough stack space for the system call but there is not,
in general, enough stack space to run a hook. Try to avoid the
problem by calling syscall directly. We only do this on GNU/Linux
for now, but it should be easy to add support for more systems with
testing. */
#if defined(__gnu_linux__)
#include <sys/syscall.h>
#if defined(SYS_mmap) || defined(SYS_mmap2)
#ifdef SYS_mmap2
#define MORESTACK_MMAP SYS_mmap2
#define MORESTACK_ADJUST_OFFSET(x) ((x) / 4096ULL)
#else
#define MORESTACK_MMAP SYS_mmap
#define MORESTACK_ADJUST_OFFSET(x) (x)
#endif
static void *
morestack_mmap (void *addr, size_t length, int prot, int flags, int fd,
off_t offset)
{
offset = MORESTACK_ADJUST_OFFSET (offset);
#ifdef __s390__
long args[6] = { (long) addr, (long) length, (long) prot, (long) flags,
(long) fd, (long) offset };
return (void *) syscall (MORESTACK_MMAP, args);
#else
return (void *) syscall (MORESTACK_MMAP, addr, length, prot, flags, fd,
offset);
#endif
}
#define mmap morestack_mmap
#endif /* defined(SYS_MMAP) || defined(SYS_mmap2) */
#if defined(SYS_munmap)
static int
morestack_munmap (void * addr, size_t length)
{
return (int) syscall (SYS_munmap, addr, length);
}
#define munmap morestack_munmap
#endif /* defined(SYS_munmap) */
#endif /* defined(__gnu_linux__) */
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;
/* Page size, as returned from getpagesize(). Set on startup. */
static unsigned int static_pagesize;
/* Set on startup to non-zero value if SPLIT_STACK_GUARD env var is set. */
static int use_guard_page;
/* 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)
{
unsigned int pagesize;
unsigned int overhead;
unsigned int allocate;
void *space;
struct stack_segment *pss;
pagesize = static_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.
Similarly, invoke getenv here to check for split-stack related control
variables, since doing do as part of the __morestack path can result
in unwanted use of SSE/AVX registers (see GCC PR 86213). */
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, static_pagesize);
/* Initialize these values here, so as to avoid dynamic linker
activity as part of a __morestack call. */
static_pagesize = getpagesize();
use_guard_page = getenv ("SPLIT_STACK_GUARD") != 0;
}
/* 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 *);
#elif defined __powerpc64__
#elif defined __s390x__
nsp -= 2 * 160;
#elif defined __s390__
nsp -= 2 * 96;
#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) */
#endif /* not powerpc 32-bit */