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More advanced emergency allocator from GCC5.1
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@earlephilhower
earlephilhower committed Nov 27, 2018
1 parent 6ca3eff commit 695e597
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27 changes: 0 additions & 27 deletions patches/gcc4.8/gcc-exception-arena.patch
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331 changes: 331 additions & 0 deletions patches/gcc4.8/gcc-exception-emergency.patch
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Original file line number Diff line number Diff line change
@@ -0,0 +1,331 @@

Modified from https://github.com/gcc-mirror/gcc/commit/ba0b98683c4e8453c35dd17c581ea59755665bc0.patch

diff --git a/libstdc++-v3/libsupc++/eh_alloc.cc b/libstdc++-v3/libsupc++/eh_alloc.cc
index 9b3fb4d..5be017c 100644
--- a/libstdc++-v3/libsupc++/eh_alloc.cc
+++ b/libstdc++-v3/libsupc++/eh_alloc.cc
@@ -34,6 +34,7 @@
#include <exception>
#include "unwind-cxx.h"
#include <ext/concurrence.h>
+#include <new>

#if _GLIBCXX_HOSTED
using std::free;
@@ -56,6 +57,11 @@ using namespace __cxxabiv1;
// so on a system with PSImode pointers we're talking about 56 bytes
// just for overhead.

+#ifdef ESP8266
+# define EMERGENCY_OBJ_SIZE 48
+# define EMERGENCY_OBJ_COUNT 4
+#else
+
#if INT_MAX == 32767
# define EMERGENCY_OBJ_SIZE 128
# define EMERGENCY_OBJ_COUNT 16
@@ -72,28 +78,175 @@ using namespace __cxxabiv1;
# define EMERGENCY_OBJ_COUNT 4
#endif

-#if INT_MAX == 32767 || EMERGENCY_OBJ_COUNT <= 32
-typedef unsigned int bitmask_type;
-#else
-#if defined (_GLIBCXX_LLP64)
-typedef unsigned long long bitmask_type;
-#else
-typedef unsigned long bitmask_type;
-#endif
#endif

+namespace
+{
+ // A fixed-size heap, variable size object allocator
+ class pool
+ {
+ public:
+ pool();
+
+ void *allocate (std::size_t);
+ void free (void *);
+
+ bool in_pool (void *);
+
+ private:
+ struct free_entry {
+ std::size_t size;
+ free_entry *next;
+ };
+ struct allocated_entry {
+ std::size_t size;
+ char data[];
+ };
+
+ // A single mutex controlling emergency allocations.
+ __gnu_cxx::__mutex emergency_mutex;
+
+ // The free-list
+ free_entry *first_free_entry;
+ // The arena itself - we need to keep track of these only
+ // to implement in_pool.
+ char *arena;
+ std::size_t arena_size;
+ };
+
+ pool::pool()
+ {
+ // Allocate the arena - we could add a GLIBCXX_EH_ARENA_SIZE environment
+ // to make this tunable.
+ arena_size = (EMERGENCY_OBJ_SIZE * EMERGENCY_OBJ_COUNT
+ + EMERGENCY_OBJ_COUNT * sizeof (__cxa_dependent_exception));
+ arena = (char *)malloc (arena_size);
+ if (!arena)
+ {
+ // If the allocation failed go without an emergency pool.
+ arena_size = 0;
+ first_free_entry = NULL;
+ return;
+ }
+
+ // Populate the free-list with a single entry covering the whole arena
+ first_free_entry = reinterpret_cast <free_entry *> (arena);
+ new (first_free_entry) free_entry;
+ first_free_entry->size = arena_size;
+ first_free_entry->next = NULL;
+ }

-typedef char one_buffer[EMERGENCY_OBJ_SIZE] __attribute__((aligned));
-static one_buffer emergency_buffer[EMERGENCY_OBJ_COUNT];
-static bitmask_type emergency_used;
+ void *pool::allocate (std::size_t size)
+ {
+ __gnu_cxx::__scoped_lock sentry(emergency_mutex);
+ // We need an additional size_t member.
+ size += sizeof (std::size_t);
+ // And we need to at least hand out objects of the size of
+ // a freelist entry.
+ if (size < sizeof (free_entry))
+ size = sizeof (free_entry);
+ // And we need to align objects we hand out to the required
+ // alignment of a freelist entry (this really aligns the
+ // tail which will become a new freelist entry).
+ size = ((size + __alignof__(free_entry) - 1)
+ & ~(__alignof__(free_entry) - 1));
+ // Search for an entry of proper size on the freelist.
+ free_entry **e;
+ for (e = &first_free_entry;
+ *e && (*e)->size < size;
+ e = &(*e)->next)
+ ;
+ if (!*e)
+ return NULL;
+ allocated_entry *x;
+ if ((*e)->size - size >= sizeof (free_entry))
+ {
+ // Slit block if it is too large.
+ free_entry *f = reinterpret_cast <free_entry *>
+ (reinterpret_cast <char *> (*e) + size);
+ std::size_t sz = (*e)->size;
+ free_entry *next = (*e)->next;
+ new (f) free_entry;
+ f->next = next;
+ f->size = sz - size;
+ x = reinterpret_cast <allocated_entry *> (*e);
+ new (x) allocated_entry;
+ x->size = size;
+ *e = f;
+ }
+ else
+ {
+ // Exact size match or too small overhead for a free entry.
+ std::size_t sz = (*e)->size;
+ free_entry *next = (*e)->next;
+ x = reinterpret_cast <allocated_entry *> (*e);
+ new (x) allocated_entry;
+ x->size = sz;
+ *e = next;
+ }
+ return &x->data;
+ }

-static __cxa_dependent_exception dependents_buffer[EMERGENCY_OBJ_COUNT];
-static bitmask_type dependents_used;
+ void pool::free (void *data)
+ {
+ __gnu_cxx::__scoped_lock sentry(emergency_mutex);
+ allocated_entry *e = reinterpret_cast <allocated_entry *>
+ (reinterpret_cast <char *> (data) - sizeof (std::size_t));
+ std::size_t sz = e->size;
+ if (!first_free_entry)
+ {
+ // If the free list is empty just put the entry there.
+ free_entry *f = reinterpret_cast <free_entry *> (e);
+ new (f) free_entry;
+ f->size = sz;
+ f->next = NULL;
+ first_free_entry = f;
+ }
+ else if (reinterpret_cast <char *> (e) + sz
+ == reinterpret_cast <char *> (first_free_entry))
+ {
+ // Check if we can merge with the first free entry being right
+ // after us.
+ free_entry *f = reinterpret_cast <free_entry *> (e);
+ new (f) free_entry;
+ f->size = sz + first_free_entry->size;
+ f->next = first_free_entry->next;
+ first_free_entry = f;
+ }
+ else
+ {
+ // Else search for a free item we can merge with at its end.
+ free_entry **fe;
+ for (fe = &first_free_entry;
+ (*fe)->next
+ && (reinterpret_cast <char *> ((*fe)->next)
+ > reinterpret_cast <char *> (e) + sz);
+ fe = &(*fe)->next)
+ ;
+ if (reinterpret_cast <char *> (*fe) + (*fe)->size
+ == reinterpret_cast <char *> (e))
+ /* Merge with the freelist entry. */
+ (*fe)->size += sz;
+ else
+ {
+ // Else put it after it which keeps the freelist sorted.
+ free_entry *f = reinterpret_cast <free_entry *> (e);
+ new (f) free_entry;
+ f->size = sz;
+ f->next = (*fe)->next;
+ (*fe)->next = f;
+ }
+ }
+ }

-namespace
-{
- // A single mutex controlling emergency allocations.
- __gnu_cxx::__mutex emergency_mutex;
+ bool pool::in_pool (void *ptr)
+ {
+ char *p = reinterpret_cast <char *> (ptr);
+ return (p > arena
+ && p < arena + arena_size);
+ }
+
+ pool emergency_pool;
}

extern "C" void *
@@ -104,30 +257,11 @@ __cxxabiv1::__cxa_allocate_exception(std::size_t thrown_size) _GLIBCXX_NOTHROW
thrown_size += sizeof (__cxa_refcounted_exception);
ret = malloc (thrown_size);

- if (! ret)
- {
- __gnu_cxx::__scoped_lock sentry(emergency_mutex);
-
- bitmask_type used = emergency_used;
- unsigned int which = 0;
-
- if (thrown_size > EMERGENCY_OBJ_SIZE)
- goto failed;
- while (used & 1)
- {
- used >>= 1;
- if (++which >= EMERGENCY_OBJ_COUNT)
- goto failed;
- }
-
- emergency_used |= (bitmask_type)1 << which;
- ret = &emergency_buffer[which][0];
-
- failed:;
+ if (!ret)
+ ret = emergency_pool.allocate (thrown_size);

- if (!ret)
- std::terminate ();
- }
+ if (!ret)
+ std::terminate ();

// We have an uncaught exception as soon as we allocate memory. This
// yields uncaught_exception() true during the copy-constructor that
@@ -144,19 +278,11 @@ __cxxabiv1::__cxa_allocate_exception(std::size_t thrown_size) _GLIBCXX_NOTHROW
extern "C" void
__cxxabiv1::__cxa_free_exception(void *vptr) _GLIBCXX_NOTHROW
{
- char *base = (char *) emergency_buffer;
- char *ptr = (char *) vptr;
- if (ptr >= base
- && ptr < base + sizeof (emergency_buffer))
- {
- const unsigned int which
- = (unsigned) (ptr - base) / EMERGENCY_OBJ_SIZE;
-
- __gnu_cxx::__scoped_lock sentry(emergency_mutex);
- emergency_used &= ~((bitmask_type)1 << which);
- }
+ char *ptr = (char *) vptr - sizeof (__cxa_refcounted_exception);
+ if (emergency_pool.in_pool (ptr))
+ emergency_pool.free (ptr);
else
- free (ptr - sizeof (__cxa_refcounted_exception));
+ free (ptr);
}


@@ -169,27 +295,11 @@ __cxxabiv1::__cxa_allocate_dependent_exception() _GLIBCXX_NOTHROW
(malloc (sizeof (__cxa_dependent_exception)));

if (!ret)
- {
- __gnu_cxx::__scoped_lock sentry(emergency_mutex);
-
- bitmask_type used = dependents_used;
- unsigned int which = 0;
-
- while (used & 1)
- {
- used >>= 1;
- if (++which >= EMERGENCY_OBJ_COUNT)
- goto failed;
- }
-
- dependents_used |= (bitmask_type)1 << which;
- ret = &dependents_buffer[which];
+ ret = static_cast <__cxa_dependent_exception*>
+ (emergency_pool.allocate (sizeof (__cxa_dependent_exception)));

- failed:;
-
- if (!ret)
- std::terminate ();
- }
+ if (!ret)
+ std::terminate ();

// We have an uncaught exception as soon as we allocate memory. This
// yields uncaught_exception() true during the copy-constructor that
@@ -207,17 +317,8 @@ extern "C" void
__cxxabiv1::__cxa_free_dependent_exception
(__cxa_dependent_exception *vptr) _GLIBCXX_NOTHROW
{
- char *base = (char *) dependents_buffer;
- char *ptr = (char *) vptr;
- if (ptr >= base
- && ptr < base + sizeof (dependents_buffer))
- {
- const unsigned int which
- = (unsigned) (ptr - base) / sizeof (__cxa_dependent_exception);
-
- __gnu_cxx::__scoped_lock sentry(emergency_mutex);
- dependents_used &= ~((bitmask_type)1 << which);
- }
+ if (emergency_pool.in_pool (vptr))
+ emergency_pool.free (vptr);
else
free (vptr);
}

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