Add load_lock to Dwfl for serializing module loading, including loading
of module's elf, dwarf, symbols as well as performing relocations.
load_lock is used only for lazy loading of these components. Hot paths
are kept lock-free using atomics. New Dwfl_Module fields elf_loaded,
dwarf_loaded and symbols_loaded have been added. These are set to
true when lazy loading of elf, dwarf and symbols is completed. They are
also set to true when initialization has been attempted and failed.
This commit serializes only the lazy loading entry points.
libdwfl/
* dwfl_begin.c (dwfl_begin): Initialize load_lock. Also move
the debuginfod_lock init to avoid NULL dereference.
* dwfl_end.c (dwfl_end): Tear down load_lock.
* dwfl_module_build_id.c (found_build_id): Store build_id_len
atomically.
(dwfl_module_build_id): Attempt to read build_id_len
atomically. If it hasn't been loaded, acquire load_lock
first.
* dwfl_module_getdwarf.c (find_symtab_locked): Renamed from
find_symtab.
(find_symtab): Wrapper for find_symtab_locked that handles
locking and checking symbols_loaded.
(get_dwarf_locked): Renamed from dwfl_module_getdwarf.
(dwfl_module_getdwarf): Wrapper for get_dwarf_locked that
handles locking and checking dwarf_loaded.
* dwfl_module_getelf.c (get_elf_locked): Renamed from
dwfl_module_getelf.
(dwfl_module_getelf): Wrapper for get_elf_locked that handles
locking and checking elf_loaded.
* dwfl_module_getsym.c (__libdwfl_getsym): Check symbols_loaded
before calling dwfl_module_getsymtab.
* libdwflP.h (struct Dwfl): Add load_lock.
(struct Dwfl_Module): Add bools symbols_loaded, dwarf_loaded
and elf_loaded.
Signed-off-by: Aaron Merey <[email protected]>
---
libdwfl/dwfl_begin.c | 4 +--
libdwfl/dwfl_end.c | 1 +
libdwfl/dwfl_module_build_id.c | 31 +++++++++++-----
libdwfl/dwfl_module_getdwarf.c | 64 ++++++++++++++++++++++++----------
libdwfl/dwfl_module_getelf.c | 33 +++++++++++++++---
libdwfl/dwfl_module_getsym.c | 3 +-
libdwfl/libdwflP.h | 8 +++++
7 files changed, 109 insertions(+), 35 deletions(-)
diff --git a/libdwfl/dwfl_begin.c b/libdwfl/dwfl_begin.c
index 835de8e3..2b029426 100644
--- a/libdwfl/dwfl_begin.c
+++ b/libdwfl/dwfl_begin.c
@@ -48,10 +48,10 @@ dwfl_begin (const Dwfl_Callbacks *callbacks)
{
dwfl->callbacks = callbacks;
dwfl->offline_next_address = OFFLINE_REDZONE;
+ mutex_init (dwfl->debuginfod_lock);
+ mutex_init (dwfl->load_lock);
}
- mutex_init (dwfl->debuginfod_lock);
-
return dwfl;
}
INTDEF (dwfl_begin)
diff --git a/libdwfl/dwfl_end.c b/libdwfl/dwfl_end.c
index c82d83fb..97516a01 100644
--- a/libdwfl/dwfl_end.c
+++ b/libdwfl/dwfl_end.c
@@ -54,6 +54,7 @@ dwfl_end (Dwfl *dwfl)
free (dwfl->lookup_segndx);
free (dwfl->sysroot);
mutex_fini (dwfl->debuginfod_lock);
+ mutex_fini (dwfl->load_lock);
Dwfl_Module *next = dwfl->modulelist;
while (next != NULL)
diff --git a/libdwfl/dwfl_module_build_id.c b/libdwfl/dwfl_module_build_id.c
index 0c198f23..c3ff08f8 100644
--- a/libdwfl/dwfl_module_build_id.c
+++ b/libdwfl/dwfl_module_build_id.c
@@ -52,7 +52,9 @@ found_build_id (Dwfl_Module *mod, bool set,
mod->build_id_bits = memcpy (copy, bits, len);
mod->build_id_vaddr = vaddr;
- mod->build_id_len = len;
+
+ /* Build id readers check len to tell if bits and vaddr are also loaded. */
+ atomic_store_release (&mod->build_id_len, len);
return len;
}
@@ -85,23 +87,34 @@ dwfl_module_build_id (Dwfl_Module *mod,
if (mod == NULL)
return -1;
- if (mod->build_id_len == 0 && mod->main.elf != NULL)
+ int len = atomic_load_acquire (&mod->build_id_len);
+ if (len == 0)
{
- /* We have the file, but have not examined it yet. */
- int result = __libdwfl_find_build_id (mod, true, mod->main.elf);
- if (result <= 0)
+ mutex_lock (mod->dwfl->load_lock);
+ len = mod->build_id_len;
+ if (len == 0 && mod->main.elf != NULL)
{
- mod->build_id_len = -1; /* Cache negative result. */
- return result;
+ /* We have the file, but have not examined it yet. */
+ len = __libdwfl_find_build_id (mod, true, mod->main.elf);
+ if (len <= 0)
+ {
+ /* Cache negative result. */
+ atomic_store_release (&mod->build_id_len, -1);
+ mutex_unlock (mod->dwfl->load_lock);
+ return len;
+ }
}
+
+ mutex_unlock (mod->dwfl->load_lock);
}
- if (mod->build_id_len <= 0)
+ if (len <= 0)
return 0;
*bits = mod->build_id_bits;
*vaddr = mod->build_id_vaddr;
- return mod->build_id_len;
+
+ return len;
}
NEW_INTDEF (dwfl_module_build_id)
diff --git a/libdwfl/dwfl_module_getdwarf.c b/libdwfl/dwfl_module_getdwarf.c
index 430c3236..247fbbd2 100644
--- a/libdwfl/dwfl_module_getdwarf.c
+++ b/libdwfl/dwfl_module_getdwarf.c
@@ -1075,12 +1075,8 @@ find_aux_sym (Dwfl_Module *mod __attribute__ ((unused)),
/* Try to find a symbol table in either MOD->main.elf or MOD->debug.elf. */
static void
-find_symtab (Dwfl_Module *mod)
+find_symtab_locked (Dwfl_Module *mod)
{
- if (mod->symdata != NULL || mod->aux_symdata != NULL /* Already done. */
- || mod->symerr != DWFL_E_NOERROR) /* Cached previous failure. */
- return;
-
__libdwfl_getelf (mod);
mod->symerr = mod->elferr;
if (mod->symerr != DWFL_E_NOERROR)
@@ -1325,6 +1321,24 @@ find_symtab (Dwfl_Module *mod)
}
}
+/* Load the symtab if it isn't already loaded. */
+static void
+find_symtab (Dwfl_Module *mod)
+{
+ if (likely (atomic_load_acquire (&mod->symbols_loaded)))
+ return;
+
+ mutex_lock (mod->dwfl->load_lock);
+ if (!mod->symbols_loaded && mod->symdata == NULL
+ && mod->aux_symdata == NULL && mod->symerr == DWFL_E_NOERROR)
+ {
+ find_symtab_locked (mod);
+ mod->symerr = __libdwfl_canon_error (mod->symerr);
+ atomic_store_release (&mod->symbols_loaded, true);
+ }
+
+ mutex_unlock (mod->dwfl->load_lock);
+}
/* Try to open a libebl backend for MOD. */
Dwfl_Error
@@ -1411,10 +1425,6 @@ load_dw (Dwfl_Module *mod, struct dwfl_file *debugfile)
static void
find_dw (Dwfl_Module *mod)
{
- if (mod->dw != NULL /* Already done. */
- || mod->dwerr != DWFL_E_NOERROR) /* Cached previous failure. */
- return;
-
__libdwfl_getelf (mod);
mod->dwerr = mod->elferr;
if (mod->dwerr != DWFL_E_NOERROR)
@@ -1471,12 +1481,9 @@ find_dw (Dwfl_Module *mod)
mod->dwerr = __libdwfl_canon_error (mod->dwerr);
}
-Dwarf *
-dwfl_module_getdwarf (Dwfl_Module *mod, Dwarf_Addr *bias)
+static void
+get_dwarf_locked (Dwfl_Module *mod)
{
- if (mod == NULL)
- return NULL;
-
find_dw (mod);
if (mod->dwerr == DWFL_E_NOERROR)
{
@@ -1489,13 +1496,34 @@ dwfl_module_getdwarf (Dwfl_Module *mod, Dwarf_Addr
*bias)
if (mod->debug.elf != mod->main.elf)
(void) __libdwfl_relocate (mod, mod->debug.elf, false);
}
+ }
+
+ atomic_store_release (&mod->dwarf_loaded, true);
+}
- *bias = dwfl_adjusted_dwarf_addr (mod, 0);
- return mod->dw;
+Dwarf *
+dwfl_module_getdwarf (Dwfl_Module *mod, Dwarf_Addr *bias)
+{
+ if (mod == NULL)
+ return NULL;
+
+ if (unlikely (!atomic_load_acquire (&mod->dwarf_loaded)))
+ {
+ mutex_lock (mod->dwfl->load_lock);
+ if (!mod->dwarf_loaded && mod->dw == NULL && mod->dwerr ==
DWFL_E_NOERROR)
+ get_dwarf_locked (mod);
+
+ mutex_unlock (mod->dwfl->load_lock);
+ }
+
+ if (mod->dwerr != DWFL_E_NOERROR)
+ {
+ __libdwfl_seterrno (mod->dwerr);
+ return NULL;
}
- __libdwfl_seterrno (mod->dwerr);
- return NULL;
+ *bias = dwfl_adjusted_dwarf_addr (mod, 0);
+ return mod->dw;
}
INTDEF (dwfl_module_getdwarf)
diff --git a/libdwfl/dwfl_module_getelf.c b/libdwfl/dwfl_module_getelf.c
index 6358de4c..e3a0197b 100644
--- a/libdwfl/dwfl_module_getelf.c
+++ b/libdwfl/dwfl_module_getelf.c
@@ -32,12 +32,9 @@
#include "libdwflP.h"
-Elf *
-dwfl_module_getelf (Dwfl_Module *mod, GElf_Addr *loadbase)
+static Elf *
+get_elf_locked (Dwfl_Module *mod, GElf_Addr *loadbase)
{
- if (mod == NULL)
- return NULL;
-
__libdwfl_getelf (mod);
if (mod->elferr == DWFL_E_NOERROR)
{
@@ -68,4 +65,30 @@ dwfl_module_getelf (Dwfl_Module *mod, GElf_Addr *loadbase)
__libdwfl_seterrno (mod->elferr);
return NULL;
}
+
+Elf *
+dwfl_module_getelf (Dwfl_Module *mod, GElf_Addr *loadbase)
+{
+ if (mod == NULL)
+ return NULL;
+
+ if (likely (atomic_load_acquire (&mod->elf_loaded)))
+ {
+ if (mod->elferr != DWFL_E_NOERROR)
+ {
+ __libdwfl_seterrno (mod->elferr);
+ return NULL;
+ }
+
+ *loadbase = dwfl_adjusted_address (mod, 0);
+ return mod->main.elf;
+ }
+
+ mutex_lock (mod->dwfl->load_lock);
+ Elf *elf = get_elf_locked (mod, loadbase);
+ atomic_store_release (&mod->elf_loaded, true);
+ mutex_unlock (mod->dwfl->load_lock);
+
+ return elf;
+}
INTDEF (dwfl_module_getelf)
diff --git a/libdwfl/dwfl_module_getsym.c b/libdwfl/dwfl_module_getsym.c
index 8de9a3eb..2bb07fd8 100644
--- a/libdwfl/dwfl_module_getsym.c
+++ b/libdwfl/dwfl_module_getsym.c
@@ -41,7 +41,8 @@ __libdwfl_getsym (Dwfl_Module *mod, int ndx, GElf_Sym *sym,
GElf_Addr *addr,
if (unlikely (mod == NULL))
return NULL;
- if (unlikely (mod->symdata == NULL))
+ if (unlikely (!atomic_load_acquire (&mod->symbols_loaded)
+ || mod->symdata == NULL))
{
int result = INTUSE(dwfl_module_getsymtab) (mod);
if (result < 0)
diff --git a/libdwfl/libdwflP.h b/libdwfl/libdwflP.h
index 56014ff6..3b4df7e8 100644
--- a/libdwfl/libdwflP.h
+++ b/libdwfl/libdwflP.h
@@ -144,6 +144,10 @@ struct Dwfl
/* Serialize debuginfod_client usage. */
mutex_define (, debuginfod_lock);
+
+ /* Serialize loading of ELF/DWARF, relocations, symbols as well as
+ Dwfl_Callbacks.*/
+ mutex_define (, load_lock);
};
#define OFFLINE_REDZONE 0x10000
@@ -206,6 +210,10 @@ struct Dwfl_Module
Dwfl_Error symerr; /* Previous failure to load symbols. */
Dwfl_Error dwerr; /* Previous failure to load DWARF. */
+ bool symbols_loaded; /* True if symbols loaded or failed to load. */
+ bool dwarf_loaded; /* True if dwarf loaded or failed to load. */
+ bool elf_loaded; /* True if elf loaded or failed to load. */
+
/* Known CU's in this module. */
struct dwfl_cu *first_cu, **cu;
--
2.56.0
