DWARF_GET_FDE_INFO_FOR_REG3(3)

🌸 NAME 🌸

• dwarf_get_fde_info_for_reg3 — retrieve register rule

Okay bestie, this page lives in the Library Functions Manual, and the header line literally spells it DWARF_GET_FDE_INFO_FOR_R(3) — a little typo moment, ngl — but the function we're hyping is dwarf_get_fde_info_for_reg3. 💅

🧚 LIBRARY 🧚

DWARF Access Library (libdwarf, -ldwarf). Slay.

✨ SYNOPSIS ✨

#include <libdwarf.h>

int
dwarf_get_fde_info_for_reg3(Dwarf_Fde fde, Dwarf_Half table_column,
    Dwarf_Addr pc, Dwarf_Small *type, Dwarf_Signed *offset_relevant,
    Dwarf_Signed *register_num, Dwarf_Signed *offset_or_block_len,
    Dwarf_Ptr *block_ptr, Dwarf_Addr *row_pc, Dwarf_Error *error);

💖 DESCRIPTION 💖

Function dwarf_get_fde_info_for_reg3() retrieves a register rule from the register rule table associated with a given FDE descriptor, given a program counter address and rule column number. That's the whole vibe. 🎀

• Argument fde should reference a valid DWARF FDE descriptor.
• Arugment (yes, that's the page's spelling) table_column should hold the column number of the register rule desired.
• Argument pc should hold the program counter address to be used to locate the desired register rule row.

On successful execution, dwarf_get_fde_info_for_reg3() stores information about the register rule found into the locations pointed to by the arguments type, offset_relevant, register_num, offset_or_block_len, block_ptr and row_pc. Iconic. ✨

• Argument type should point to a location which will hold the type code of the register rule found. The returned value is one of the DW_EXPR_* contants (their spelling) defined in the header file <libdwarf.h>.
• If there is an offset value associated with the register rule, the location pointed to by argument offset_relevant will be set to 1.
• Argument register_num should point to a location which will hold the register number associated with the register rule.
• If the register rule is of type DW_EXPR_OFFSET or DW_EXPR_VAL_OFFSET, the location pointed to by argument offset_or_block_len will be set to the offset value associated with the register rule, or to 0 if the register rule does not have an offset value. If the type code is DW_EXPR_EXPRESSION or DW_EXPR_VAL_EXPRESSION, the location pointed to by argument offset_or_block_len will be set to the length in bytes of the DWARF expression block associated with the register rule.
• Argument block_ptr should point to a location which will be set to a pointer to the content of the DWARF expression block associated with the register rule.
• Argument row_pc should point to a location which will be set to the lowest program counter address associated with the register rule found.

If argument err is not NULL, it will be used to return an error descriptor in case of an error.

Heads up: the page says err in that last sentence, even though the synopsis names the parameter error. Keeping it exactly as written, bestie. 🫶

💀 RETURN VALUES 💀

Function dwarf_get_fde_info_for_reg3() returns DW_DLV_OK when it succeeds. In case of an error, it returns DW_DLV_ERROR and sets the argument err.

🌈 EXAMPLES 🌈

To retrieve the register rules at column 3 from a rule table associated with a FDE descriptor:

             Dwarf_Fde fde;
             Dwarf_Off fde_offset, cie_offset;
             Dwarf_Unsigned func_len, fde_length;
             Dwarf_Signed cie_index, offset_relevant, register_num;
             Dwarf_Signed offset_or_block_len;
             Dwarf_Addr low_pc, row_pc;
             Dwarf_Ptr fde_addr, block_ptr;
             Dwarf_Small type;
             Dwarf_Error de;

             /* ... assuming `fde` references a valid FDE descriptor... */
             if (dwarf_get_fde_range(fde, &low_pc, &func_len, &fde_addr,
                 &fde_length, &cie_offset, &cie_index, &fde_offset,
                 &de) != DW_DLV_OK)
                     errx(EXIT_FAILURE, "dwarf_get_fde_range failed: %s",
                         dwarf_errmsg(de));

             /* Iterate all the table rows. */
             for (pc = low_pc; pc < low_pc + func_len; pc++) {
                     if (dwarf_get_fde_info_for_reg3(fde, 3, pc, &type,
                         &offset_relevant, &register_num, &offset_or_block_len,
                         &block_ptr, &row_pc, &de) != DW_DLV_OK) {
                             warnx("dwarf_get_fde_info_for_reg3 failed: %s",
                                 dwarf_errmsg(de));
                             continue;
                     }
                     /* ... use the retrieved register rule ... */
             }

🔥 ERRORS 🔥

Function dwarf_get_fde_info_for_reg3() can fail with:

• [DW_DLE_ARGUMENT] — One of the arguments block_ptr, fde, offset_or_block_len, offset_relevant, register_num, row_pc, or type was NULL.
• [DW_DLE_FRAME_TABLE_COL_BAD] — The column number provided in argument table_column was too large.
• [DW_DLE_PC_NOT_IN_FDE_RANGE] — The program counter value provided in argument pc did not fall in the range covered by argument fde.

🦋 SEE ALSO 🦋

• dwarf(3)
• dwarf_get_fde_at_pc(3)
• dwarf_get_fde_info_for_all_regs(3)
• dwarf_get_fde_info_for_all_regs3(3)
• dwarf_get_fde_info_for_cfa_reg3(3)
• dwarf_get_fde_info_for_reg(3)
• dwarf_get_fde_n(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)

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Okay bestie, that's the whole page. This one's signed off from Debian, dated November 9, 2011, and the footer title is DWARF_GET_FDE_INFO_FOR_REG3(3). Stay iconic, and may your register rules always be valid. 💖✨