[PATCH] D36313: [llvm-dwarfdump] - Print section name and index when dumping .debug_info ranges

[George Rimar via Phabricator via llvm-commits]

grimar added inline comments.


================
Comment at: lib/DebugInfo/DWARF/DWARFContext.cpp:1044
 public:
   DWARFObjInMemory(const StringMap<std::unique_ptr<MemoryBuffer>> &Sections,
                    uint8_t AddrSize, bool IsLittleEndian)
----------------
dblaikie wrote:
> If/how do section indexes work in this codepath? Are they provided & printed but without names (because the section itself cannot be looked up)? Is there a way to support that? (probably not necessary, but consistency is nice where it's possible)
Currently I think only 2 tools use `DIContext::dump()` call: `llvm-dwarfdump` and `llvm-objdump`,
both are creating `DWARFObjInMemory` using another codepatch, where `ObjectFile` is provided.
If it is not, then `getSectionName()` (introduced in this patch) would just return empty section name
for any index, because it checks `Obj` member and takes section index from it. 

But that is not so simple to implement because currently we take `SectionIndex` from relocations and
this constructor assumes to take relocated data. That mean we have no section index to take from.

Fortunately tools do not need it. I would leave this place as is.


================
Comment at: lib/DebugInfo/DWARF/DWARFContext.cpp:1194-1200
+    StringRef Ret;
+    if (Obj) {
+      auto SecI = Obj->section_begin();
+      std::advance(SecI, Index);
+      (*SecI).getName(Ret);
+    }
+    return Ret;
----------------
dblaikie wrote:
> Maybe invert this for an early return:
> 
>   if (!Obj)
>     return "";
>   return std::next(Obj->sections(), Index)->getName(Ret);
Done.


================
Comment at: lib/DebugInfo/DWARF/DWARFDie.cpp:64
+
+    std::string NameIndex = "N/A";
+    if (Range.SectionIndex != -1ULL)
----------------
aprantl wrote:
> dblaikie wrote:
> > Rather than creating a temporary string, maybe move this to after the format line, and print it directly to the stream with a format call as well?
> I think I would prefer an empty string instead of "N/A".
Done.


================
Comment at: lib/DebugInfo/DWARF/DWARFDie.cpp:64-67
+    std::string NameIndex = "N/A";
+    if (Range.SectionIndex != -1ULL)
+      NameIndex = Obj.getSectionName(Range.SectionIndex).str() + "(" +
+                  std::to_string(Range.SectionIndex) + ")";
----------------
grimar wrote:
> aprantl wrote:
> > dblaikie wrote:
> > > Rather than creating a temporary string, maybe move this to after the format line, and print it directly to the stream with a format call as well?
> > I think I would prefer an empty string instead of "N/A".
> Done.
Done.


================
Comment at: test/DebugInfo/X86/dwarfdump-ranges-unrelocated.s:7-8
+# CHECK: DW_AT_ranges [DW_FORM_sec_offset] (0x00000000
+# CHECK-NEXT:  [0x0000000000000000 - 0x0000000000000001) .text.foo1(3)
+# CHECK-NEXT:  [0x0000000000000000 - 0x0000000000000002) .text.foo2(4))
+
----------------
dblaikie wrote:
> It'd be nice to columnize the section number  - but maybe that's too much work? (scanning through to find the longest section name, etc)
> 
> Also, similar amount of work: Do you think it'd be worth it/good to omit the section number if the section names are not ambiguous in this list? (or perhaps necessary to only do this if the name is not ambiguous in the whole file (so you on't look at the ranges for two functions and see them describing what appears to be the same section))
> 
> & what about omitting the name or putting it somewhere else (like at the start on a separate line) if every entry is in the same section? (which will be the case for all ranges except the compile_unit ranges, most likely)
> 
> Maybe that's all overkill - wouldn't mind getting Adrian's take on this, as he was driving a bunch of the dwarfdump improvements like this inline range dumping.
I would not scan over all sections of file, because it looks too much. Scanning over all sections can be slow.
I would not omit something dependent on third conditions too, because it makes logic of output unclear for
people that are not familar with tool. ("Why it prints section index for "foo" and does not for "bar" ? BUUUG !")

Also I think often I am looking for section number in readelf/objdump/other tools, so I would not omit
it to be able to find it as fast as possible without manual eye-mapping name to index by myself.

Basing on above I think I like "omitting the name or putting it somewhere else (like at the start on a separate line) if every entry is in the same section" as it avoids printing the same name+index multiple times.
It also removes need to columnize anything probably and thus scan through to find longest index/section name, what should leave code simple.

What do you think about new version of output ? (I am wondering if we still want to columnize the section index, I am not sure).


================
Comment at: test/DebugInfo/dwarfdump-ranges.test:7-8
 CHECK:  DW_AT_ranges [DW_FORM_data4]      (0x00000000
-CHECK-NEXT:          [0x000000000000062c - 0x0000000000000637)
-CHECK-NEXT:          [0x0000000000000637 - 0x000000000000063d))
+CHECK-NEXT:          [0x000000000000062c - 0x0000000000000637) N/A
+CHECK-NEXT:          [0x0000000000000637 - 0x000000000000063d) N/A)
 
----------------
dblaikie wrote:
> Why does this print N/A in this test case?
dwarfdump-test4.elf-x86-64 is not an object but DSO. It does not have .rel[a] sections
(targeted to debug sections I mean), and so all `RelocAddrMaps` are empty and we can not
take `SectionIndex` from relocation.


https://reviews.llvm.org/D36313