Re: [PATCH 4/4] libbacktrace: get debug information for loaded dlls

[Ian Lance Taylor <iant@google.com>]

On Fri, Jan 20, 2023 at 2:55 AM Björn Schäpers <gcc@hazardy.de> wrote:
>
> From: Björn Schäpers <bjoern@hazardy.de>
>
> Fixes https://github.com/ianlancetaylor/libbacktrace/issues/53, except
> that libraries loaded after the backtrace_initialize are not handled.
> But as far as I can see that's the same for elf.

Thanks, but I don't want a patch that loops using goto statements.
Please rewrite to avoid that.  It may be simpler to call a function.

Also starting with a module count of 1000 seems like a lot.  Do
typical Windows programs load that many modules?

Ian




> Tested on x86_64-linux and i686-w64-mingw32.
>
> -- >8 --
>
>         * pecoff.c (coff_add): New argument for the module handle of the
>         file, to get the base address.
>         * pecoff.c (backtrace_initialize): Iterate over loaded libraries
>         and call coff_add.
>
> Signed-off-by: Björn Schäpers <bjoern@hazardy.de>
> ---
>  libbacktrace/pecoff.c | 76 ++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 72 insertions(+), 4 deletions(-)
>
> diff --git a/libbacktrace/pecoff.c b/libbacktrace/pecoff.c
> index 296f1357b5f..40395109e51 100644
> --- a/libbacktrace/pecoff.c
> +++ b/libbacktrace/pecoff.c
> @@ -49,6 +49,7 @@ POSSIBILITY OF SUCH DAMAGE.  */
>  #endif
>
>  #include <windows.h>
> +#include <psapi.h>
>  #endif
>
>  /* Coff file header.  */
> @@ -592,7 +593,8 @@ coff_syminfo (struct backtrace_state *state, uintptr_t addr,
>  static int
>  coff_add (struct backtrace_state *state, int descriptor,
>           backtrace_error_callback error_callback, void *data,
> -         fileline *fileline_fn, int *found_sym, int *found_dwarf)
> +         fileline *fileline_fn, int *found_sym, int *found_dwarf,
> +         uintptr_t module_handle ATTRIBUTE_UNUSED)
>  {
>    struct backtrace_view fhdr_view;
>    off_t fhdr_off;
> @@ -623,7 +625,6 @@ coff_add (struct backtrace_state *state, int descriptor,
>    int is_64;
>    uintptr_t image_base;
>    uintptr_t base_address = 0;
> -  uintptr_t module_handle;
>    struct dwarf_sections dwarf_sections;
>
>    *found_sym = 0;
> @@ -871,7 +872,6 @@ coff_add (struct backtrace_state *state, int descriptor,
>      }
>
>  #ifdef HAVE_WINDOWS_H
> -    module_handle = (uintptr_t) GetModuleHandleW (NULL);
>      base_address = module_handle - image_base;
>  #endif
>
> @@ -914,12 +914,80 @@ backtrace_initialize (struct backtrace_state *state,
>    int found_sym;
>    int found_dwarf;
>    fileline coff_fileline_fn;
> +  uintptr_t module_handle = 0;
> +
> +#ifdef HAVE_WINDOWS_H
> +  DWORD i;
> +  DWORD module_count;
> +  DWORD bytes_needed_for_modules;
> +  HMODULE *modules;
> +  char module_name[MAX_PATH];
> +  int module_found_sym;
> +  fileline module_fileline_fn;
> +
> +  module_handle = (uintptr_t) GetModuleHandleW (NULL);
> +#endif
>
>    ret = coff_add (state, descriptor, error_callback, data,
> -                 &coff_fileline_fn, &found_sym, &found_dwarf);
> +                 &coff_fileline_fn, &found_sym, &found_dwarf, module_handle);
>    if (!ret)
>      return 0;
>
> +#ifdef HAVE_WINDOWS_H
> +  module_count = 1000;
> + alloc_modules:
> +  modules = backtrace_alloc (state, module_count * sizeof(HMODULE),
> +                            error_callback, data);
> +  if (modules == NULL)
> +    goto skip_modules;
> +  if (!EnumProcessModules (GetCurrentProcess (), modules, module_count,
> +                          &bytes_needed_for_modules))
> +    {
> +      error_callback(data, "Could not enumerate process modules",
> +                    (int) GetLastError ());
> +      goto free_modules;
> +    }
> +  if (bytes_needed_for_modules > module_count * sizeof(HMODULE))
> +    {
> +      backtrace_free (state, modules, module_count * sizeof(HMODULE),
> +                     error_callback, data);
> +      // Add an extra of 2, if some module is loaded in another thread.
> +      module_count = bytes_needed_for_modules / sizeof(HMODULE) + 2;
> +      modules = NULL;
> +      goto alloc_modules;
> +    }
> +
> +  for (i = 0; i < bytes_needed_for_modules / sizeof(HMODULE); ++i)
> +    {
> +      if (GetModuleFileNameA (modules[i], module_name, MAX_PATH - 1))
> +       {
> +         if (strcmp (filename, module_name) == 0)
> +           continue;
> +
> +         module_handle = (uintptr_t) GetModuleHandleA (module_name);
> +         if (module_handle == 0)
> +           continue;
> +
> +         descriptor = backtrace_open (module_name, error_callback, data, NULL);
> +         if (descriptor < 0)
> +           continue;
> +
> +         coff_add (state, descriptor, error_callback, data,
> +                   &module_fileline_fn, &module_found_sym, &found_dwarf,
> +                   module_handle);
> +         if (module_found_sym)
> +           found_sym = 1;
> +       }
> +    }
> +
> + free_modules:
> +  if (modules)
> +    backtrace_free(state, modules, module_count * sizeof(HMODULE),
> +                  error_callback, data);
> +  modules = NULL;
> + skip_modules:
> +#endif
> +
>    if (!state->threaded)
>      {
>        if (found_sym)
> --
> 2.38.1
>