diff options
author | Jonathon Anderson <jma14@rice.edu> | 2019-08-25 10:07:00 -0500 |
---|---|---|
committer | Mark Wielaard <mark@klomp.org> | 2019-11-08 17:14:52 +0100 |
commit | 32cd9c4ad5b888da9c4f94a702a02d380b2a745b (patch) | |
tree | a797f90d2a2844d8dd1e297c2d33f4a6948f6086 | |
parent | 5e2a8e25e2b76066ef8a7976225f9ed1d959ce03 (diff) |
libdw: Rewrite the memory handler to be more robust.
Pthread's thread-local variables are highly limited, which makes
it difficult to use many Dwarfs. This replaces that with a
less efficient (or elegant) but more robust method.
Signed-off-by: Jonathon Anderson <jma14@rice.edu>
-rw-r--r-- | libdw/ChangeLog | 9 | ||||
-rw-r--r-- | libdw/dwarf_begin_elf.c | 7 | ||||
-rw-r--r-- | libdw/dwarf_end.c | 24 | ||||
-rw-r--r-- | libdw/libdwP.h | 67 | ||||
-rw-r--r-- | libdw/libdw_alloc.c | 68 |
5 files changed, 122 insertions, 53 deletions
diff --git a/libdw/ChangeLog b/libdw/ChangeLog index 2bcb642f..d308172b 100644 --- a/libdw/ChangeLog +++ b/libdw/ChangeLog @@ -1,3 +1,12 @@ +2019-10-28 Jonathon Anderson <jma14@rice.edu> + + * libdw_alloc.c: Added __libdw_alloc_tail. + (__libdw_allocate): Switch to use the mem_tails array. + * libdwP.h (Dwarf): Likewise. + * dwarf_begin_elf.c (dwarf_begin_elf): Support for above. + * dwarf_end.c (dwarf_end): Likewise. + * atomics.h: Add support for thread_local. + 2019-10-28 Mark Wielaard <mark@klomp.org> * dwarf_sig8_hash.h: Include libdw.h. Remove COMPARE. Include diff --git a/libdw/dwarf_begin_elf.c b/libdw/dwarf_begin_elf.c index 8c116847..85343088 100644 --- a/libdw/dwarf_begin_elf.c +++ b/libdw/dwarf_begin_elf.c @@ -430,13 +430,14 @@ dwarf_begin_elf (Elf *elf, Dwarf_Cmd cmd, Elf_Scn *scngrp) actual allocation. */ result->mem_default_size = mem_default_size; result->oom_handler = __libdw_oom; - if (pthread_key_create (&result->mem_key, NULL) != 0) + if (pthread_rwlock_init(&result->mem_rwl, NULL) != 0) { free (result); - __libdw_seterrno (DWARF_E_NOMEM); /* no memory or max pthread keys. */ + __libdw_seterrno (DWARF_E_NOMEM); /* no memory. */ return NULL; } - atomic_init (&result->mem_tail, (uintptr_t)NULL); + result->mem_stacks = 0; + result->mem_tails = NULL; if (cmd == DWARF_C_READ || cmd == DWARF_C_RDWR) { diff --git a/libdw/dwarf_end.c b/libdw/dwarf_end.c index 7e194a55..77f537a7 100644 --- a/libdw/dwarf_end.c +++ b/libdw/dwarf_end.c @@ -100,17 +100,19 @@ dwarf_end (Dwarf *dwarf) tdestroy (dwarf->split_tree, noop_free); /* Free the internally allocated memory. */ - struct libdw_memblock *memp; - memp = (struct libdw_memblock *) (atomic_load_explicit - (&dwarf->mem_tail, - memory_order_relaxed)); - while (memp != NULL) - { - struct libdw_memblock *prevp = memp->prev; - free (memp); - memp = prevp; - } - pthread_key_delete (dwarf->mem_key); + for (size_t i = 0; i < dwarf->mem_stacks; i++) + { + struct libdw_memblock *memp = dwarf->mem_tails[i]; + while (memp != NULL) + { + struct libdw_memblock *prevp = memp->prev; + free (memp); + memp = prevp; + } + } + if (dwarf->mem_tails != NULL) + free (dwarf->mem_tails); + pthread_rwlock_destroy (&dwarf->mem_rwl); /* Free the pubnames helper structure. */ free (dwarf->pubnames_sets); diff --git a/libdw/libdwP.h b/libdw/libdwP.h index ad2599eb..3e1ef59b 100644 --- a/libdw/libdwP.h +++ b/libdw/libdwP.h @@ -149,17 +149,6 @@ enum #include "dwarf_sig8_hash.h" -/* Structure for internal memory handling. This is basically a simplified - reimplementation of obstacks. Unfortunately the standard obstack - implementation is not usable in libraries. */ -struct libdw_memblock -{ - size_t size; - size_t remaining; - struct libdw_memblock *prev; - char mem[0]; -}; - /* This is the structure representing the debugging state. */ struct Dwarf { @@ -231,11 +220,22 @@ struct Dwarf /* Similar for addrx/constx, which will come from .debug_addr section. */ struct Dwarf_CU *fake_addr_cu; - /* Internal memory handling. Each thread allocates separately and only - allocates from its own blocks, while all the blocks are pushed atomically - onto a unified stack for easy deallocation. */ - pthread_key_t mem_key; - atomic_uintptr_t mem_tail; + /* Supporting lock for internal memory handling. Ensures threads that have + an entry in the mem_tails array are not disturbed by new threads doing + allocations for this Dwarf. */ + pthread_rwlock_t mem_rwl; + + /* Internal memory handling. This is basically a simplified thread-local + reimplementation of obstacks. Unfortunately the standard obstack + implementation is not usable in libraries. */ + size_t mem_stacks; + struct libdw_memblock + { + size_t size; + size_t remaining; + struct libdw_memblock *prev; + char mem[0]; + } **mem_tails; /* Default size of allocated memory blocks. */ size_t mem_default_size; @@ -578,34 +578,31 @@ libdw_valid_user_form (int form) extern void __libdw_seterrno (int value) internal_function; -/* Memory handling, the easy parts. This macro does not do nor need to do any - locking for proper concurrent operation. */ +/* Memory handling, the easy parts. */ #define libdw_alloc(dbg, type, tsize, cnt) \ - ({ struct libdw_memblock *_tail = pthread_getspecific (dbg->mem_key); \ - size_t _req = (tsize) * (cnt); \ - type *_result; \ - if (unlikely (_tail == NULL)) \ - _result = (type *) __libdw_allocate (dbg, _req, __alignof (type)); \ + ({ struct libdw_memblock *_tail = __libdw_alloc_tail(dbg); \ + size_t _required = (tsize) * (cnt); \ + type *_result = (type *) (_tail->mem + (_tail->size - _tail->remaining));\ + size_t _padding = ((__alignof (type) \ + - ((uintptr_t) _result & (__alignof (type) - 1))) \ + & (__alignof (type) - 1)); \ + if (unlikely (_tail->remaining < _required + _padding)) \ + _result = (type *) __libdw_allocate (dbg, _required, __alignof (type));\ else \ { \ - _result = (type *) (_tail->mem + (_tail->size - _tail->remaining)); \ - size_t _padding = ((__alignof (type) \ - - ((uintptr_t) _result & (__alignof (type) - 1))) \ - & (__alignof (type) - 1)); \ - if (unlikely (_tail->remaining < _req + _padding)) \ - _result = (type *) __libdw_allocate (dbg, _req, __alignof (type)); \ - else \ - { \ - _req += _padding; \ - _result = (type *) ((char *) _result + _padding); \ - _tail->remaining -= _req; \ - } \ + _required += _padding; \ + _result = (type *) ((char *) _result + _padding); \ + _tail->remaining -= _required; \ } \ _result; }) #define libdw_typed_alloc(dbg, type) \ libdw_alloc (dbg, type, sizeof (type), 1) +/* Callback to choose a thread-local memory allocation stack. */ +extern struct libdw_memblock *__libdw_alloc_tail (Dwarf* dbg) + __nonnull_attribute__ (1); + /* Callback to allocate more. */ extern void *__libdw_allocate (Dwarf *dbg, size_t minsize, size_t align) __attribute__ ((__malloc__)) __nonnull_attribute__ (1); diff --git a/libdw/libdw_alloc.c b/libdw/libdw_alloc.c index f2e74d18..0eb02c34 100644 --- a/libdw/libdw_alloc.c +++ b/libdw/libdw_alloc.c @@ -35,7 +35,67 @@ #include <stdlib.h> #include "libdwP.h" #include "system.h" +#include "atomics.h" +#if USE_VG_ANNOTATIONS == 1 +#include <helgrind.h> +#else +#define ANNOTATE_HAPPENS_BEFORE(X) +#define ANNOTATE_HAPPENS_AFTER(X) +#endif +#define THREAD_ID_UNSET ((size_t) -1) +static __thread size_t thread_id = THREAD_ID_UNSET; +static atomic_size_t next_id = ATOMIC_VAR_INIT(0); + +struct libdw_memblock * +__libdw_alloc_tail (Dwarf *dbg) +{ + if (thread_id == THREAD_ID_UNSET) + thread_id = atomic_fetch_add (&next_id, 1); + + pthread_rwlock_rdlock (&dbg->mem_rwl); + if (thread_id >= dbg->mem_stacks) + { + pthread_rwlock_unlock (&dbg->mem_rwl); + pthread_rwlock_wrlock (&dbg->mem_rwl); + + /* Another thread may have already reallocated. In theory using an + atomic would be faster, but given that this only happens once per + thread per Dwarf, some minor slowdown should be fine. */ + if (thread_id >= dbg->mem_stacks) + { + dbg->mem_tails = realloc (dbg->mem_tails, (thread_id+1) + * sizeof (struct libdw_memblock *)); + if (dbg->mem_tails == NULL) + { + pthread_rwlock_unlock (&dbg->mem_rwl); + dbg->oom_handler(); + } + for (size_t i = dbg->mem_stacks; i <= thread_id; i++) + dbg->mem_tails[i] = NULL; + dbg->mem_stacks = thread_id + 1; + ANNOTATE_HAPPENS_BEFORE (&dbg->mem_tails); + } + + pthread_rwlock_unlock (&dbg->mem_rwl); + pthread_rwlock_rdlock (&dbg->mem_rwl); + } + + /* At this point, we have an entry in the tail array. */ + ANNOTATE_HAPPENS_AFTER (&dbg->mem_tails); + struct libdw_memblock *result = dbg->mem_tails[thread_id]; + if (result == NULL) + { + result = malloc (dbg->mem_default_size); + result->size = dbg->mem_default_size + - offsetof (struct libdw_memblock, mem); + result->remaining = result->size; + result->prev = NULL; + dbg->mem_tails[thread_id] = result; + } + pthread_rwlock_unlock (&dbg->mem_rwl); + return result; +} void * __libdw_allocate (Dwarf *dbg, size_t minsize, size_t align) @@ -52,10 +112,10 @@ __libdw_allocate (Dwarf *dbg, size_t minsize, size_t align) newp->size = size - offsetof (struct libdw_memblock, mem); newp->remaining = (uintptr_t) newp + size - (result + minsize); - newp->prev = (struct libdw_memblock*)atomic_exchange_explicit( - &dbg->mem_tail, (uintptr_t)newp, memory_order_relaxed); - if (pthread_setspecific (dbg->mem_key, newp) != 0) - dbg->oom_handler (); + pthread_rwlock_rdlock (&dbg->mem_rwl); + newp->prev = dbg->mem_tails[thread_id]; + dbg->mem_tails[thread_id] = newp; + pthread_rwlock_unlock (&dbg->mem_rwl); return (void *) result; } |