DWARF_GET_FDE_LIST(3)

💅 DWARF_GET_FDE_LIST(3) — Library Functions Manual

okay so first things first bestie: this is a page from the DWARF Access Library manual — that's libdwarf, link it with -ldwarf and you're golden ✨

---

🎀 NAME 🎀

dwarf_get_fde_list — retrieve frame information

📚 LIBRARY 📚

DWARF Access Library (libdwarf, -ldwarf)

✨ SYNOPSIS ✨

#include <libdwarf.h>

int
dwarf_get_fde_list(Dwarf_Debug dbg, Dwarf_Cie **cie_list,
    Dwarf_Signed *cie_count, Dwarf_Fde **fde_list,
    Dwarf_Signed *fde_count, Dwarf_Error *err);

int
dwarf_get_fde_list_eh(Dwarf_Debug dbg, Dwarf_Cie **cie_list,
    Dwarf_Signed *cie_count, Dwarf_Fde **fde_list,
    Dwarf_Signed *fde_count, Dwarf_Error *err);

🦋 DESCRIPTION 🦋

So these two functions go and grab all your frame related information for the DWARF debug context you point them at. Like, they pull up the whole frame situation for you 🫶

Here's the tea on who pulls from where:

• dwarf_get_fde_list() grabs frame info out of the DWARF section named .debug_frame.
• dwarf_get_fde_list_eh() is for objects that carry GNU style C++ exception handling information — it grabs frame info from the section named .eh_frame. iykyk 💅

Frame info comes back to you as opaque descriptors of type Dwarf_Cie and Dwarf_Fde. And like — they're opaque, so you can't just peek inside. Applications need to use the other frame related functions in the DWARF(3) API set to actually retrieve the information chilling inside these descriptors. main character energy only through the proper API, no cap 🔥

now the arguments, one by one, because we're being thorough:

• Argument dbg should reference a DWARF debug context allocated using dwarf_init(3).
• Argument cie_list should point to a location that will be set to a pointer to an array of Dwarf_Cie descriptors.
• Argument cie_count should point to a location that will be set to the number of Dwarf_Cie descriptors returned.
• Argument fde_list should point to a location that will be set to a pointer to an array of Dwarf_Fde descriptors.
• Argument fde_count should point to a location that will be set to the number of Dwarf_Fde descriptors returned.
• If argument err is not NULL, it will be used to store error information in case of an error. 🙈

🧠 Memory Management 🧠

okay this part is important, listen up:

The memory areas used for the arrays returned in arguments cie_list and fde_list are owned by the DWARF Access Library (libdwarf, -ldwarf). Application code should not attempt to directly free these areas. 😭

Portable applications should instead use the dwarf_fde_cie_list_dealloc(3) function to indicate that these memory areas may be freed. That's the vibe-check-approved way 🎀

🌈 RETURN VALUES 🌈

On success, these functions returns DW_DLV_OK. 👑

They return DW_DLV_NO_ENTRY if there is no frame information associated with the given DWARF debug context. (like, nothing to see here, moving on 💀)

In case of an error, they return DW_DLV_ERROR and set the argument err.

🍓 EXAMPLES 🍓

To obtain frame information from the .debug_frame section, use:

      Dwarf_Debug dbg;
      Dwarf_Cie *cie_list, cie;
      Dwarf_Fde *fde_list, fde;
      Dwarf_Off fde_offset, cie_offset;
      Dwarf_Unsigned func_len, fde_length, fde_instlen;
      Dwarf_Signed cie_count, fde_count, cie_index;
      Dwarf_Addr low_pc;
      Dwarf_Ptr fde_addr, fde_inst, cie_inst;
      Dwarf_Error de;
      int i;

      if (dwarf_get_fde_list(dbg, &cie_list, &cie_count,
          &fde_list, &fde_count, &de) != DW_DLV_OK) {
              errx(EXIT_FAILURE, "dwarf_get_fde_list failed: %s",
                  dwarf_errmsg(de));
      }

      for (i = 0; i < fde_count; i++) {
              if (dwarf_get_fde_n(fde_list, i, &fde, &de) != DW_DLV_OK) {
                      warnx("dwarf_get_fde_n failed: %s",
                          dwarf_errmsg(de));
                      continue;
              }
              if (dwarf_get_cie_of_fde(fde, &cie, &de) != DW_DLV_OK) {
                      warnx("dwarf_get_fde_n failed: %s",
                          dwarf_errmsg(de));
                      continue;
              }
              if (dwarf_get_fde_range(fde, &low_pc, &func_len, &fde_addr,
                  &fde_length, &cie_offset, &cie_index, &fde_offset,
                  &de) != DW_DLV_OK) {
                      warnx("dwarf_get_fde_range failed: %s",
                          dwarf_errmsg(de));
                      continue;
              }
              if (dwarf_get_fde_instr_bytes(fde, &fde_inst, &fde_instlen,
                  &de) != DW_DLV_OK) {
                      warnx("dwarf_get_fde_instr_bytes failed: %s",
                          dwarf_errmsg(de));
                      continue;
              }

              /* ... Use the retrieved frame information ... */
      }

      /* Indicate that the returned arrays may be freed. */
      dwarf_fde_cie_list_dealloc(dbg, cie_list, cie_count, fde_list,
          fde_count);

like, obsessed with how clean that is 🧚

💀 ERRORS 💀

These functions may fail with the following errors:

• [DW_DLE_ARGUMENT] — One of the arguments dbg, cie_list, cie_count, fde_list or fde_count was NULL. (bestie, you forgot to pass something 😭)
• [DW_DLE_NO_ENTRY] — There is no frame information associated with the giving DWARF debug context.

👑 SEE ALSO 👑

dwarf(3), dwarf_fde_cie_list_dealloc(3), dwarf_get_cie_index(3), dwarf_get_cie_of_fde(3), dwarf_get_fde_at_pc(3), dwarf_get_fde_instr_bytes(3), dwarf_get_fde_n(3), dwarf_get_fde_range(3), dwarf_set_frame_cfa_value(3), dwarf_set_frame_rule_initial_value(3), dwarf_set_frame_rule_table_size(3), dwarf_set_frame_same_value(3), dwarf_set_frame_undefined_value(3)

---

💖 and that's the whole page, bestie — this one's from Debian, dated November 9, 2011, living at DWARF_GET_FDE_LIST(3). slay, go read some stack frames 🦋✨