[glibc] backtrace: Implement on top of <unwind-link.h>

[glibc] backtrace: Implement on top of <unwind-link.h>

[Florian Weimer]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=e164d95abff6ad46c91ceb29fd688f9f03ca8a74

commit e164d95abff6ad46c91ceb29fd688f9f03ca8a74
Author: Florian Weimer <fweimer@redhat.com>
Date:   Mon Mar 1 15:56:36 2021 +0100

    backtrace: Implement on top of <unwind-link.h>
    
    This reimplements the generic version of backtrace.
    
    Reviewed-by: Carlos O'Donell <carlos@redhat.com>

Diff:
---
 debug/backtrace.c | 84 +++++++++++--------------------------------------------
 1 file changed, 17 insertions(+), 67 deletions(-)

diff --git a/debug/backtrace.c b/debug/backtrace.c
index 5ded57bfc4..187d911a0d 100644
--- a/debug/backtrace.c
+++ b/debug/backtrace.c
@@ -17,10 +17,7 @@
    License along with the GNU C Library; if not, see
    <https://www.gnu.org/licenses/>.  */
 
-#include <libc-lock.h>
-#include <dlfcn.h>
 #include <execinfo.h>
-#include <gnu/lib-names.h>
 #include <stdlib.h>
 #include <unwind.h>
 #include <unwind-link.h>
@@ -28,47 +25,12 @@
 struct trace_arg
 {
   void **array;
+  struct unwind_link *unwind_link;
   _Unwind_Word cfa;
   int cnt;
   int size;
 };
 
-#ifdef SHARED
-static _Unwind_Reason_Code (*unwind_backtrace) (_Unwind_Trace_Fn, void *);
-static _Unwind_Ptr (*unwind_getip) (struct _Unwind_Context *);
-static _Unwind_Word (*unwind_getcfa) (struct _Unwind_Context *);
-static void *libgcc_handle;
-
-
-/* Dummy version in case libgcc_s does not contain the real code.  */
-static _Unwind_Word
-dummy_getcfa (struct _Unwind_Context *ctx __attribute__ ((unused)))
-{
-  return 0;
-}
-
-
-static void
-init (void)
-{
-  libgcc_handle = __libc_dlopen (LIBGCC_S_SO);
-
-  if (libgcc_handle == NULL)
-    return;
-
-  unwind_backtrace = __libc_dlsym (libgcc_handle, "_Unwind_Backtrace");
-  unwind_getip = __libc_dlsym (libgcc_handle, "_Unwind_GetIP");
-  if (unwind_getip == NULL)
-    unwind_backtrace = NULL;
-  unwind_getcfa = (__libc_dlsym (libgcc_handle, "_Unwind_GetCFA")
-		  ?: dummy_getcfa);
-}
-#else
-# define unwind_backtrace _Unwind_Backtrace
-# define unwind_getip _Unwind_GetIP
-# define unwind_getcfa _Unwind_GetCFA
-#endif
-
 static _Unwind_Reason_Code
 backtrace_helper (struct _Unwind_Context *ctx, void *a)
 {
@@ -78,14 +40,16 @@ backtrace_helper (struct _Unwind_Context *ctx, void *a)
      Skip it.  */
   if (arg->cnt != -1)
     {
-      arg->array[arg->cnt] = (void *) unwind_getip (ctx);
+      arg->array[arg->cnt]
+	= (void *) UNWIND_LINK_PTR (arg->unwind_link, _Unwind_GetIP) (ctx);
       if (arg->cnt > 0)
 	arg->array[arg->cnt]
 	  = unwind_arch_adjustment (arg->array[arg->cnt - 1],
 				    arg->array[arg->cnt]);
 
       /* Check whether we make any progress.  */
-      _Unwind_Word cfa = unwind_getcfa (ctx);
+      _Unwind_Word cfa
+	= UNWIND_LINK_PTR (arg->unwind_link, _Unwind_GetCFA) (ctx);
 
       if (arg->cnt > 0 && arg->array[arg->cnt - 1] == arg->array[arg->cnt]
 	 && cfa == arg->cfa)
@@ -100,20 +64,20 @@ backtrace_helper (struct _Unwind_Context *ctx, void *a)
 int
 __backtrace (void **array, int size)
 {
-  struct trace_arg arg = { .array = array, .cfa = 0, .size = size, .cnt = -1 };
-
-  if (size <= 0)
-    return 0;
-
-#ifdef SHARED
-  __libc_once_define (static, once);
-
-  __libc_once (once, init);
-  if (unwind_backtrace == NULL)
+  struct trace_arg arg =
+    {
+     .array = array,
+     .unwind_link = __libc_unwind_link_get (),
+     .cfa = 0,
+     .size = size,
+     .cnt = -1
+    };
+
+  if (size <= 0 || arg.unwind_link == NULL)
     return 0;
-#endif
 
-  unwind_backtrace (backtrace_helper, &arg);
+  UNWIND_LINK_PTR (arg.unwind_link, _Unwind_Backtrace)
+    (backtrace_helper, &arg);
 
   /* _Unwind_Backtrace seems to put NULL address above
      _start.  Fix it up here.  */
@@ -123,17 +87,3 @@ __backtrace (void **array, int size)
 }
 weak_alias (__backtrace, backtrace)
 libc_hidden_def (__backtrace)
-
-
-#ifdef SHARED
-/* Free all resources if necessary.  */
-libc_freeres_fn (free_mem)
-{
-  unwind_backtrace = NULL;
-  if (libgcc_handle != NULL)
-    {
-      __libc_dlclose (libgcc_handle);
-      libgcc_handle = NULL;
-    }
-}
-#endif