searchSymtab

pub fn searchSymtab(ef: *ElfFile, gpa: Allocator, vaddr: u64) error{
    NoSymtab,
    NoStrtab,
    BadSymtab,
    OutOfMemory,
}!std.debug.Symbol {
    const symtab = ef.symtab orelse return error.NoSymtab;
    const strtab = ef.strtab orelse return error.NoStrtab;

    if (symtab.bytes.len % symtab.entry_size != 0) return error.BadSymtab;

    const swap_endian = ef.endian != @import("builtin").cpu.arch.endian();

    switch (ef.is_64) {
        inline true, false => |is_64| {
            const Sym = if (is_64) elf.Elf64_Sym else elf.Elf32_Sym;
            if (symtab.entry_size != @sizeOf(Sym)) return error.BadSymtab;
            const symbols: []align(1) const Sym = @ptrCast(symtab.bytes);
            if (ef.symbol_search_table == null) {
                ef.symbol_search_table = try buildSymbolSearchTable(gpa, ef.endian, Sym, symbols);
            }
            const search_table = ef.symbol_search_table.?;
            const SearchContext = struct {
                swap_endian: bool,
                target: u64,
                symbols: []align(1) const Sym,
                fn predicate(ctx: @This(), sym_index: usize) bool {
                    // We need to return `true` for the first N items, then `false` for the rest --
                    // the index we'll get out is the first `false` one. So, we'll return `true` iff
                    // the target address is after the *end* of this symbol. This synchronizes with
                    // the logic in `buildSymbolSearchTable` which sorts by *end* address.
                    var sym = ctx.symbols[sym_index];
                    if (ctx.swap_endian) std.mem.byteSwapAllFields(Sym, &sym);
                    const sym_end = sym.st_value + sym.st_size;
                    return ctx.target >= sym_end;
                }
            };
            const sym_index_index = std.sort.partitionPoint(usize, search_table, @as(SearchContext, .{
                .swap_endian = swap_endian,
                .target = vaddr,
                .symbols = symbols,
            }), SearchContext.predicate);
            if (sym_index_index == search_table.len) return .unknown;
            var sym = symbols[search_table[sym_index_index]];
            if (swap_endian) std.mem.byteSwapAllFields(Sym, &sym);
            if (vaddr < sym.st_value or vaddr >= sym.st_value + sym.st_size) return .unknown;
            return .{
                .name = std.mem.sliceTo(strtab[sym.st_name..], 0),
                .compile_unit_name = null,
                .source_location = null,
            };
        },
    }
}