[Bug libc/31405] Switch dl_load_write_lock to rwlock for better ASAN performance

["adhemerval.zanella at linaro dot org" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=31405

Adhemerval Zanella <adhemerval.zanella at linaro dot org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |adhemerval.zanella at linaro dot o
                   |                            |rg

--- Comment #1 from Adhemerval Zanella <adhemerval.zanella at linaro dot org> ---
I think we can use _dl_find_object instead, as used on libbacktrace for other
ABIs. The API was designed for exactly this scalability issue and
dlfo_eh_frame/dlfo_eh_count maps to PT_ARM_EXIDX vaddr start and length on ARM.


diff --git a/sysdeps/arm/find_exidx.c b/sysdeps/arm/find_exidx.c
index d647865e5a..a7a76b09da 100644
--- a/sysdeps/arm/find_exidx.c
+++ b/sysdeps/arm/find_exidx.c
@@ -16,64 +16,15 @@
    <https://www.gnu.org/licenses/>.  */

 #include <link.h>
-#include <unwind.h>
-
-struct unw_eh_callback_data
-{
-  _Unwind_Ptr pc;
-  _Unwind_Ptr exidx_start;
-  int exidx_len;
-};
-
-
-/* Callback to determines if the PC lies within an object, and remember the
-   location of the exception index table if it does.  */
-
-static int
-find_exidx_callback (struct dl_phdr_info * info, size_t size, void * ptr)
-{
-  struct unw_eh_callback_data * data;
-  const ElfW(Phdr) *phdr;
-  int i;
-  int match;
-  _Unwind_Ptr load_base;
-
-  data = (struct unw_eh_callback_data *) ptr;
-  load_base = info->dlpi_addr;
-  phdr = info->dlpi_phdr;
-
-  match = 0;
-  for (i = info->dlpi_phnum; i > 0; i--, phdr++)
-    {
-      if (phdr->p_type == PT_LOAD)
-        {
-          _Unwind_Ptr vaddr = phdr->p_vaddr + load_base;
-          if (data->pc >= vaddr && data->pc < vaddr + phdr->p_memsz)
-            match = 1;
-        }
-      else if (phdr->p_type == PT_ARM_EXIDX)
-       {
-         data->exidx_start = (_Unwind_Ptr) (phdr->p_vaddr + load_base);
-         data->exidx_len = phdr->p_memsz;
-       }
-    }
-
-  return match;
-}
-

 /* Find the exception index table containing PC.  */

 _Unwind_Ptr
 __gnu_Unwind_Find_exidx (_Unwind_Ptr pc, int * pcount)
 {
-  struct unw_eh_callback_data data;
-
-  data.pc = pc;
-  data.exidx_start = 0;
-  if (__dl_iterate_phdr (find_exidx_callback, &data) <= 0)
+  struct dl_find_object data;
+  if (_dl_find_object ((void *) pc, &data) < 0)
     return 0;
-
-  *pcount = data.exidx_len / 8;
-  return data.exidx_start;
+  *pcount = data.dlfo_eh_count;
+  return (_Unwind_Ptr) data.dlfo_eh_frame;
 }

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