[PATCH] D32492: [llvm-dwarfdump] - Change format for .gdb_index dump.

Wed Apr 26 14:26:52 PDT 2017

I'd have a mild preference for [x, y) and also okay with x – y without the [) around the pair.  The [x – y) does just look funny. Although of course in context it's clear what's intended, so it's just a mild preference.
--paulr

From: llvm-commits [mailto:llvm-commits-bounces at lists.llvm.org] On Behalf Of David Blaikie via llvm-commits
Sent: Wednesday, April 26, 2017 10:41 AM
To: reviews+D32492+public+d04ad76ab213883a at reviews.llvm.org; grimar at accesssoftek.com; dccitaliano at gmail.com; rafael.espindola at gmail.com; Adrian Prantl
Cc: llvm-commits at lists.llvm.org
Subject: Re: [PATCH] D32492: [llvm-dwarfdump] - Change format for .gdb_index dump.

On Wed, Apr 26, 2017 at 3:31 AM George Rimar via Phabricator <reviews at reviews.llvm.org<mailto:reviews at reviews.llvm.org>> wrote:
grimar added inline comments.

================
Comment at: lib/DebugInfo/DWARF/DWARFGdbIndex.cpp:42
     OS << format(
-        "    Low address = 0x%llx, High address = 0x%llx, CU index = %d\n",
-        Addr.LowAddress, Addr.HighAddress, Addr.CuIndex);
+        "    Low/High address = [0x%llx, 0x%llx] (Size: 0x%llx), CU id = %d\n",
+        Addr.LowAddress, Addr.HighAddress, Addr.HighAddress - Addr.LowAddress,
----------------
dblaikie wrote:
> While you're here, probably makes sense to fix the range to render as [x, y) rather than [x, y] ? (since it's a half open range, if I recall correctly)
I am not sure I understand why it is half open. If I got your idea correctly then probably output would be:
```
[a, b) (c, d) (e, f) (g, h]

Nah, more like:

[a, b)
[c, d)
[e, f)
[g, h)

```

But I do not think it would be correct.
.gdb_index format (https://sourceware.org/gdb/onlinedocs/gdb/Index-Section-Format.html) defines address area as:
> The address area. The address area consists of a sequence of address entries. Each address entry has three elements:
> The low address. This is a 64-bit little-endian value.
> The high address. This is a 64-bit little-endian value. Like DW_AT_high_pc, the value is one byte beyond the end.

This bit here ^ "the value is one byte beyond the end" is what I mean by a half open range.

If a range in a range list includes bytes at offset/address 5, 6, 7, and 8. Then the range would be emitted as "5, 9" which is half open or written mathematically [5, 9)

( https://en.wikipedia.org/wiki/Interval_(mathematics) - "A half-open interval includes only one of its endpoints, and is denoted by mixing the notations for open and closed intervals. (0,1] means greater than 0 and less than or equal to 1, while [0,1) means greater than or equal to 0 and less than 1.")

> The CU index. This is an offset_type value.
>

So we have set of elements that have begining and end marks. It looks to be set of closed segments/snippets, if I am not missing something, so I think [x, y] is more appropriate then.

I was interested how readelf dumps the .gdb_index for the same file used in testcase.
It was:
readelf --debug-dump=gdb_index dwarfdump-gdbindex-v7.elf-x86-64
```
Contents of the .gdb_index section:
Version 7

CU table:
[  0] 0x0 - 0x33
[  1] 0x34 - 0x67

TU table:

Address table:
00000000004000e8 00000000004000f3 0
00000000004000f3 00000000004000fe 1

Symbol table:
[489] main: 0 [global, function]
[754] int:
        0 [static, type]
        1 [static, type]
[956] main2: 1 [global, function]
```

Basing on above I can suggest 2 solutions:
1) Leave [x, y] as is.
2) Change dump output to something that avoids use of []() if that can be confusing, for example to:

```
Address area offset = 0x38, has 2 entries:
0x4000e8 - 0x4000f3, Size = 0xb, CU id = 0
0x4000f3 - 0x4000fe, Size = 0xb, CU id = 1
```

What do you think ?

'-' could be ambiguous with the minus sign here.

Indeed llvm-dwarfdump uses the half open range notation [x, y) in the DW_AT_ranges dumping such as here:
  DW_AT_ranges [DW_FORM_sec_offset] (0x00000000
     [0x00000000004004f0 - 0x00000000004004f6)
     [0x0000000000400500 - 0x0000000000400508))

though it also uses - rather than ','... which is weird.

Adrian - what do you reckon we should standardize on here? I do sort of get the x - y syntax, but it seems a bit awkward when combined with the [x, y) syntax (which I also like, for clarity about the boundaries). I'd tend to lean towards [x, y)? But I could live with sticking with the [x - y)

https://reviews.llvm.org/D32492

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20170426/52f0200b/attachment.html>