3

我正在尝试将 DW_AT_data_member_location 属性值从 dwarf 信息打印到，get the member variables offset from a struct name但似乎没有帮助函数起作用。

这是来自的 dwarf_info objdump：

<1><1bf>: Abbrev Number: 5 (DW_TAG_structure_type)
<1c0>   DW_AT_name        : (indirect string, offset: 0xf0): class  
<1c4>   DW_AT_byte_size   : 208 
<1c5>   DW_AT_decl_file   : 1   
<1c6>   DW_AT_decl_line   : 10  
<1c7>   DW_AT_sibling     : <0x1f8> 
<2><1cb>: Abbrev Number: 6 (DW_TAG_member)
<1cc>   DW_AT_name        : (indirect string, offset: 0xc7): schools    
<1d0>   DW_AT_decl_file   : 1   
<1d1>   DW_AT_decl_line   : 11  
<1d2>   DW_AT_type        : <0x1f8> 
<1d6>   DW_AT_data_member_location: 2 byte block: 23 0  (DW_OP_plus_uconst: 0)
<2><1d9>: Abbrev Number: 6 (DW_TAG_member)
<1da>   DW_AT_name        : (indirect string, offset: 0xd8): size   
<1de>   DW_AT_decl_file   : 1   
<1df>   DW_AT_decl_line   : 12  
<1e0>   DW_AT_type        : <0x159> 
<1e4>   DW_AT_data_member_location: 3 byte block: 23 c8 1   (DW_OP_plus_uconst: 200)
<2><1e8>: Abbrev Number: 6 (DW_TAG_member)
<1e9>   DW_AT_name        : (indirect string, offset: 0xf6): record 
<1ed>   DW_AT_decl_file   : 1   
<1ee>   DW_AT_decl_line   : 13  
<1ef>   DW_AT_type        : <0x1b8> 
<1f3>   DW_AT_data_member_location: 3 byte block: 23 cc 1   (DW_OP_plus_uconst: 204)

我能够获得属性代码但不能获得属性值：

 if(dwarf_whatattr(attrs[i],&attrcode,&error) != DW_DLV_OK)
                      printf("Error");

 printf("Attrcode: %d\n",attrcode); // This one works

 if(attrcode==DW_AT_data_member_location) 
           dwarf_formudata(attrs[i],&offset,0) // This one does not work

这个变量的类型是什么？如何获得它的价值？哪个辅助函数可以在这里工作？

4

2 回答 2

3

DWARF 调试格式允许将成员的偏移量表示为简单的常量或需要计算偏移量的表达式。无论出于何种原因，您尝试处理的调试信息都以表达式的形式表达了一个简单的常量偏移量。您需要“评估”表达式以确定偏移量是多少。像这样的东西：

if (attrcode == DW_AT_data_member_location) {
    Dwarf_Half form;
    dwarf_whatform(attrs[i], &form, &error);
    if (form == DW_FORM_data1 || form == DW_FORM_data2
        form == DW_FORM_data2 || form == DW_FORM_data4
        form == DW_FORM_data8 || form == DW_FORM_udata) {
        dwarf_formudata(attrs[i], &offset, 0);
    } else if (form == DW_FORM_sdata) {
        Dwarf_Signed soffset;
        dwarf_formsdata(attrs[i], &soffset, 0);
        if (soffset < 0) {
             printf("unsupported negative offset\n");
             /* FAIL */
        }
        offset = (Dwarf_Unsigned) soffset;
    } else {
        Dwarf_Locdesc **locdescs;
        Dwarf_Signed len;
        if (dwarf_loclist_n(attrs[i], &locdescs, &len,  &error) == DW_DLV_ERROR) {
             printf("unsupported member offset\n");
             /* FAIL */
        }
        if (len != 1
            || locdescs[0]->ld_cents != 1
            || (locdescs[0]->ld_s[0]).lr_atom != DW_OP_plus_uconst) {
             printf("unsupported location expression\n");
             /* FAIL */
        }
        offset = (locdescs[0]->ld_s[0]).lr_number;
    }
}
于 2014-07-31T00:55:23.653 回答
1

如果您更喜欢使用 JVM，我编写了一个用于解析 dwarf 的简单库，它创建了一个基于 EMF 的模型。下面是打印结构成员位置的示例代码：

def someFunction() {
  var elf = new Elf32Context(buffer)
  var dwarf = new Dwarf32Context(elf)
  var model = DwarfModelFactory::createModel(dwarf)
  model.eAllContents.filter(StructureType).forEach[it.dumpStruct]
}


def dumpStruct(CompositeType struct) '''
  «switch(struct) {StructureType:'struct' UnionType:'union' default:'composite?'}» «struct.typedef?.name» {
    «FOR m : struct.members»
        «m.type.dumpType» «m.name»  @«m.dataMemberLocation»
    «ENDFOR»
  }
'''
于 2015-09-07T00:14:58.727 回答