Improve __libdw_dieabbrev performance by removing abbrev_lock. This
lock protects the Dwarf_Die abbrev member due to lazy loading.
Instead, eagerly load abbrev during Dwarf_Die initialization so that
the member is readonly and requires no locking.
Signed-off-by: Aaron Merey <ame...@redhat.com>
---
libdw/dwarf_decl_file.c | 3 +-
libdw/dwarf_end.c | 1 -
libdw/dwarf_getscopevar.c | 3 +-
libdw/libdwP.h | 65 +++++++++++++++++----------------------
libdw/libdw_findcu.c | 1 -
5 files changed, 32 insertions(+), 41 deletions(-)
diff --git a/libdw/dwarf_decl_file.c b/libdw/dwarf_decl_file.c
index 1b91a4e9..03040e12 100644
--- a/libdw/dwarf_decl_file.c
+++ b/libdw/dwarf_decl_file.c
@@ -50,7 +50,8 @@ dwarf_decl_file (Dwarf_Die *die)
Dwarf_Files *files;
size_t nfiles;
- if (INTUSE(dwarf_getsrcfiles) (&CUDIE (attr_mem.cu), &files, &nfiles) != 0)
+ Dwarf_Die cudie = CUDIE (attr_mem.cu);
+ if (INTUSE(dwarf_getsrcfiles) (&cudie, &files, &nfiles) != 0)
return NULL;
if (idx >= nfiles)
diff --git a/libdw/dwarf_end.c b/libdw/dwarf_end.c
index 1628e448..51021d64 100644
--- a/libdw/dwarf_end.c
+++ b/libdw/dwarf_end.c
@@ -68,7 +68,6 @@ cu_free (void *arg)
&& p != p->dbg->fake_addr_cu)
{
Dwarf_Abbrev_Hash_free (&p->abbrev_hash);
- rwlock_fini (p->abbrev_lock);
rwlock_fini (p->split_lock);
mutex_fini (p->src_lock);
mutex_fini (p->str_off_base_lock);
diff --git a/libdw/dwarf_getscopevar.c b/libdw/dwarf_getscopevar.c
index 7b1416f3..306ccae0 100644
--- a/libdw/dwarf_getscopevar.c
+++ b/libdw/dwarf_getscopevar.c
@@ -40,7 +40,8 @@
static int
getfiles (Dwarf_Die *die, Dwarf_Files **files)
{
- return INTUSE(dwarf_getsrcfiles) (&CUDIE (die->cu), files, NULL);
+ Dwarf_Die cudie = CUDIE (die->cu);
+ return INTUSE(dwarf_getsrcfiles) (&cudie, files, NULL);
}
/* Fetch an attribute that should have a constant integer form. */
diff --git a/libdw/libdwP.h b/libdw/libdwP.h
index de80cd4e..4a528c9c 100644
--- a/libdw/libdwP.h
+++ b/libdw/libdwP.h
@@ -455,10 +455,6 @@ struct Dwarf_CU
Don't access directly, call __libdw_cu_locs_base. */
Dwarf_Off locs_base;
- /* Synchronize access to the abbrev member of a Dwarf_Die that
- refers to this Dwarf_CU. Covers __libdw_die_abbrev. */
- rwlock_define(, abbrev_lock);
-
/* Synchronize access to the split member of this Dwarf_CU.
Covers __libdw_find_split_unit. */
rwlock_define(, split_lock);
@@ -595,23 +591,6 @@ __libdw_first_die_off_from_cu (struct Dwarf_CU *cu)
cu->unit_type);
}
-#define CUDIE(fromcu) \
- ((Dwarf_Die) \
- { \
- .cu = (fromcu), \
- .addr = ((char *) (fromcu)->dbg->sectiondata[cu_sec_idx (fromcu)]->d_buf \
- + __libdw_first_die_off_from_cu (fromcu)) \
- })
-
-#define SUBDIE(fromcu) \
- ((Dwarf_Die) \
- { \
- .cu = (fromcu), \
- .addr = ((char *) (fromcu)->dbg->sectiondata[cu_sec_idx (fromcu)]->d_buf \
- + (fromcu)->start + (fromcu)->subdie_offset) \
- })
-
-
/* Prototype of a single .debug_macro operator. */
typedef struct
{
@@ -820,12 +799,7 @@ __nonnull_attribute__ (1)
__libdw_dieabbrev (Dwarf_Die *die, const unsigned char **readp)
{
if (unlikely (die->cu == NULL))
- {
- die->abbrev = DWARF_END_ABBREV;
- return DWARF_END_ABBREV;
- }
-
- rwlock_wrlock (die->cu->abbrev_lock);
+ return DWARF_END_ABBREV;
/* Do we need to get the abbreviation, or need to read after the code? */
if (die->abbrev == NULL || readp != NULL)
@@ -835,25 +809,20 @@ __libdw_dieabbrev (Dwarf_Die *die, const unsigned char
**readp)
const unsigned char *addr = die->addr;
if (addr >= (const unsigned char *) die->cu->endp)
- {
- die->abbrev = DWARF_END_ABBREV;
- rwlock_unlock (die->cu->abbrev_lock);
- return DWARF_END_ABBREV;
- }
+ return DWARF_END_ABBREV;
get_uleb128 (code, addr, die->cu->endp);
if (readp != NULL)
*readp = addr;
- /* Find the abbreviation. */
+ /* Find the abbreviation. To improve performance, this write is not
+ protected by a lock. It should only be reachable by a single thread
+ when initializing the DIE. */
if (die->abbrev == NULL)
die->abbrev = __libdw_findabbrev (die->cu, code);
}
- Dwarf_Abbrev *result = die->abbrev;
- rwlock_unlock (die->cu->abbrev_lock);
-
- return result;
+ return die->abbrev;
}
/* Helper functions for form handling. */
@@ -1112,6 +1081,28 @@ cu_sec_idx (struct Dwarf_CU *cu)
return cu->sec_idx;
}
+static inline Dwarf_Die
+CUDIE (Dwarf_CU *fromcu)
+{
+ Dwarf_Die res = {0};
+ res.cu = fromcu;
+ res.addr = ((char *) (fromcu)->dbg->sectiondata[cu_sec_idx (fromcu)]->d_buf
+ + __libdw_first_die_off_from_cu (fromcu));
+ (void) dwarf_tag (&res); /* Set .abbrev */
+ return res;
+}
+
+static inline Dwarf_Die
+SUBDIE (Dwarf_CU *fromcu)
+{
+ Dwarf_Die res = {0};
+ res.cu = fromcu;
+ res.addr = ((char *) (fromcu)->dbg->sectiondata[cu_sec_idx (fromcu)]->d_buf
+ + (fromcu)->start + (fromcu)->subdie_offset);
+ (void) dwarf_tag (&res); /* Set .abbrev */
+ return res;
+}
+
static inline bool
is_cudie (Dwarf_Die *cudie)
{
diff --git a/libdw/libdw_findcu.c b/libdw/libdw_findcu.c
index 0e4dcc37..857ebd38 100644
--- a/libdw/libdw_findcu.c
+++ b/libdw/libdw_findcu.c
@@ -177,7 +177,6 @@ __libdw_intern_next_unit (Dwarf *dbg, bool debug_types)
newp->startp = data->d_buf + newp->start;
newp->endp = data->d_buf + newp->end;
eu_search_tree_init (&newp->locs_tree);
- rwlock_init (newp->abbrev_lock);
rwlock_init (newp->split_lock);
mutex_init (newp->src_lock);
mutex_init (newp->str_off_base_lock);
--
2.49.0
