[PATCH 04/10] i386: Implement backtrace on top of <unwind-link.h>

[Carlos O'Donell]

On 2/17/21 11:03 AM, Florian Weimer via Libc-alpha wrote:

LGTM. And the i386 version.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

> ---
>  sysdeps/i386/backtrace.c | 82 +++++++++-------------------------------
>  1 file changed, 18 insertions(+), 64 deletions(-)
> 
> diff --git a/sysdeps/i386/backtrace.c b/sysdeps/i386/backtrace.c
> index 124b0b73e3..4631f68fdc 100644
> --- a/sysdeps/i386/backtrace.c
> +++ b/sysdeps/i386/backtrace.c
> @@ -17,52 +17,18 @@
>     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 <stdlib.h>
> -#include <unwind.h>
> +#include <unwind-link.h>
>  
>  struct trace_arg
>  {
>    void **array;
> +  struct unwind_link *unwind_link;
>    int cnt, size;
>    void *lastebp, *lastesp;
>  };
>  
> -#ifdef SHARED
> -static _Unwind_Reason_Code (*unwind_backtrace) (_Unwind_Trace_Fn, void *);
> -static _Unwind_Ptr (*unwind_getip) (struct _Unwind_Context *);
> -static _Unwind_Ptr (*unwind_getcfa) (struct _Unwind_Context *);
> -static _Unwind_Ptr (*unwind_getgr) (struct _Unwind_Context *, int);
> -static void *libgcc_handle;
> -
> -static void
> -init (void)
> -{
> -  libgcc_handle = __libc_dlopen ("libgcc_s.so.1");
> -
> -  if (libgcc_handle == NULL)
> -    return;
> -
> -  unwind_backtrace = __libc_dlsym (libgcc_handle, "_Unwind_Backtrace");
> -  unwind_getip = __libc_dlsym (libgcc_handle, "_Unwind_GetIP");
> -  unwind_getcfa = __libc_dlsym (libgcc_handle, "_Unwind_GetCFA");
> -  unwind_getgr = __libc_dlsym (libgcc_handle, "_Unwind_GetGR");
> -  if (unwind_getip == NULL || unwind_getgr == NULL || unwind_getcfa == NULL)
> -    {
> -      unwind_backtrace = NULL;
> -      __libc_dlclose (libgcc_handle);
> -      libgcc_handle = NULL;
> -    }
> -}
> -#else
> -# define unwind_backtrace _Unwind_Backtrace
> -# define unwind_getip _Unwind_GetIP
> -# define unwind_getcfa _Unwind_GetCFA
> -# define unwind_getgr _Unwind_GetGR
> -#endif
> -
>  static _Unwind_Reason_Code
>  backtrace_helper (struct _Unwind_Context *ctx, void *a)
>  {
> @@ -71,13 +37,16 @@ backtrace_helper (struct _Unwind_Context *ctx, void *a)
>    /* We are first called with address in the __backtrace function.
>       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 == arg->size)
>      return _URC_END_OF_STACK;
>  
>    /* %ebp is DWARF2 register 5 on IA-32.  */
> -  arg->lastebp = (void *) unwind_getgr (ctx, 5);
> -  arg->lastesp = (void *) unwind_getcfa (ctx);
> +  arg->lastebp
> +    = (void *) UNWIND_LINK_PTR (arg->unwind_link, _Unwind_GetGR) (ctx, 5);
> +  arg->lastesp
> +    = (void *) UNWIND_LINK_PTR (arg->unwind_link, _Unwind_GetCFA) (ctx);
>    return _URC_NO_REASON;
>  }
>  
> @@ -111,20 +80,19 @@ struct layout
>  int
>  __backtrace (void **array, int size)
>  {
> -  struct trace_arg arg = { .array = array, .size = size, .cnt = -1 };
> -
> -  if (size <= 0)
> -    return 0;
> -
> -#ifdef SHARED
> -  __libc_once_define (static, once);
> +  struct trace_arg arg =
> +    {
> +     .array = array,
> +     .unwind_link = __libc_unwind_link_get (),
> +     .size = size,
> +     .cnt = -1,
> +    };
>  
> -  __libc_once (once, init);
> -  if (unwind_backtrace == NULL)
> +  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);
>  
>    if (arg.cnt > 1 && arg.array[arg.cnt - 1] == NULL)
>      --arg.cnt;
> @@ -147,17 +115,3 @@ __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
> 


-- 
Cheers,
Carlos.