[arch-general] debug package repositories again
Joe Julian
me at joejulian.name
Thu Aug 13 17:09:00 UTC 2015
On 08/13/2015 06:47 AM, Leonid Isaev wrote:
> On Thu, Aug 13, 2015 at 03:11:58PM +0200, Evan Penner wrote:
>>>> I would personally prefer that most packages come with debugging enabled
>>>> by
>>>> default. Surely, there will be a performance cost, but speed is not
>>>> crucial in
>>>> most cases.
>>>>
>>>> Cheers,
>>>>
>>> There's no performance impact, just disk space and bandwidth.
>>>
>> Bandwidth is probably the main problem, although anyone who wants to debug
>> will probably be fine with that.
> I think you guys misunderstood me. The biggest problem IMHO with building debug
> versions locally is not compiling itself, but setting up the environment. So, I
> meant that packages come with debugging enabled (compiled with gcc -O0 -g and
> perhaps ./configure options). This way, there will be not many new packages.
No, the biggest problem with building debug versions locally is that it
takes hours of developer time multiplied by every bug found. Why are we
wasting such a limited resource when it's so easy not to? Life is finite.
>
> Of course, this is not a good idea for things like FF/Gnome/KDE because of a
> slow-down, but a performance penalty for smaller programs like vim, links,
> XFCE4 etc. will not be noticeable (at least I don't see any for a self-compiled
> xfce4 desktop on a single-core Intel Atom based netbook).
>
> Cheers,
What is this slow-down you keep talking about? I'm not asking to do away
with optimization, just give us a way to get the debug symbols without
rebuilding. The debug symbols are located in totally different sections
from the code/data sections. You can check it with objdump:
$ objdump -h a.out
a.out: file format elf64-x86-64
Sections:
Idx Name Size VMA LMA File
off Algn
0 .interp 0000001c 0000000000400200 0000000000400200
00000200 2**0
CONTENTS, ALLOC, LOAD, READONLY, DATA
1 .note.ABI-tag 00000020 000000000040021c 000000000040021c
0000021c 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
2 .note.gnu.build-id 00000024 000000000040023c 000000000040023c
0000023c 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
3 .hash 00000018 0000000000400260 0000000000400260
00000260 2**3
CONTENTS, ALLOC, LOAD, READONLY, DATA
4 .gnu.hash 0000001c 0000000000400278 0000000000400278
00000278 2**3
CONTENTS, ALLOC, LOAD, READONLY, DATA
5 .dynsym 00000048 0000000000400298 0000000000400298
00000298 2**3
CONTENTS, ALLOC, LOAD, READONLY, DATA
6 .dynstr 00000038 00000000004002e0 00000000004002e0
000002e0 2**0
CONTENTS, ALLOC, LOAD, READONLY, DATA
7 .gnu.version 00000006 0000000000400318 0000000000400318
00000318 2**1
CONTENTS, ALLOC, LOAD, READONLY, DATA
8 .gnu.version_r 00000020 0000000000400320 0000000000400320
00000320 2**3
CONTENTS, ALLOC, LOAD, READONLY, DATA
9 .rela.dyn 00000018 0000000000400340 0000000000400340
00000340 2**3
CONTENTS, ALLOC, LOAD, READONLY, DATA
10 .rela.plt 00000018 0000000000400358 0000000000400358
00000358 2**3
CONTENTS, ALLOC, LOAD, READONLY, DATA
11 .init 00000018 0000000000400370 0000000000400370
00000370 2**2
CONTENTS, ALLOC, LOAD, READONLY, CODE
12 .plt 00000020 0000000000400388 0000000000400388
00000388 2**2
CONTENTS, ALLOC, LOAD, READONLY, CODE
13 .text 000001c8 00000000004003b0 00000000004003b0
000003b0 2**4
CONTENTS, ALLOC, LOAD, READONLY, CODE
14 .fini 0000000e 0000000000400578 0000000000400578
00000578 2**2
CONTENTS, ALLOC, LOAD, READONLY, CODE
15 .rodata 00000004 0000000000400588 0000000000400588
00000588 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
16 .eh_frame_hdr 00000024 000000000040058c 000000000040058c
0000058c 2**2
CONTENTS, ALLOC, LOAD, READONLY, DATA
17 .eh_frame 0000007c 00000000004005b0 00000000004005b0
000005b0 2**3
CONTENTS, ALLOC, LOAD, READONLY, DATA
18 .ctors 00000010 0000000000600630 0000000000600630
00000630 2**3
CONTENTS, ALLOC, LOAD, DATA
19 .dtors 00000010 0000000000600640 0000000000600640
00000640 2**3
CONTENTS, ALLOC, LOAD, DATA
20 .jcr 00000008 0000000000600650 0000000000600650
00000650 2**3
CONTENTS, ALLOC, LOAD, DATA
21 .dynamic 000001a0 0000000000600658 0000000000600658
00000658 2**3
CONTENTS, ALLOC, LOAD, DATA
22 .got 00000008 00000000006007f8 00000000006007f8
000007f8 2**3
CONTENTS, ALLOC, LOAD, DATA
23 .got.plt 00000020 0000000000600800 0000000000600800
00000800 2**3
CONTENTS, ALLOC, LOAD, DATA
24 .data 00000010 0000000000600820 0000000000600820
00000820 2**3
CONTENTS, ALLOC, LOAD, DATA
25 .bss 00000010 0000000000600830 0000000000600830
00000830 2**3
ALLOC
26 .comment 00000039 0000000000000000 0000000000000000
00000830 2**0
CONTENTS, READONLY
27 .debug_aranges 00000030 0000000000000000 0000000000000000
00000869 2**0
CONTENTS, READONLY, DEBUGGING
28 .debug_pubnames 0000001b 0000000000000000 0000000000000000
00000899 2**0
CONTENTS, READONLY, DEBUGGING
29 .debug_info 00000055 0000000000000000 0000000000000000
000008b4 2**0
CONTENTS, READONLY, DEBUGGING
30 .debug_abbrev 00000034 0000000000000000 0000000000000000
00000909 2**0
CONTENTS, READONLY, DEBUGGING
31 .debug_line 0000003b 0000000000000000 0000000000000000
0000093d 2**0
CONTENTS, READONLY, DEBUGGING
32 .debug_str 00000026 0000000000000000 0000000000000000
00000978 2**0
CONTENTS, READONLY, DEBUGGING
33 .debug_loc 0000004c 0000000000000000 0000000000000000
0000099e 2**0
CONTENTS, READONLY, DEBUGGING
You can see the extra sections (27 through 33). These sections won't be
loaded at runtime, so there won't be any performance penalty. Using gdb,
you can also examine them at runtime
$ gdb ./a.out
(gdb) break main
(gdb) run
(gdb) info files
// blah blah ....
Local exec file:
`/home/kghost/a.out', file type elf64-x86-64.
Entry point: 0x4003b0
0x0000000000400200 - 0x000000000040021c is .interp
0x000000000040021c - 0x000000000040023c is .note.ABI-tag
0x000000000040023c - 0x0000000000400260 is .note.gnu.build-id
0x0000000000400260 - 0x0000000000400278 is .hash
0x0000000000400278 - 0x0000000000400294 is .gnu.hash
0x0000000000400298 - 0x00000000004002e0 is .dynsym
0x00000000004002e0 - 0x0000000000400318 is .dynstr
0x0000000000400318 - 0x000000000040031e is .gnu.version
0x0000000000400320 - 0x0000000000400340 is .gnu.version_r
0x0000000000400340 - 0x0000000000400358 is .rela.dyn
0x0000000000400358 - 0x0000000000400370 is .rela.plt
0x0000000000400370 - 0x0000000000400388 is .init
0x0000000000400388 - 0x00000000004003a8 is .plt
0x00000000004003b0 - 0x0000000000400578 is .text
0x0000000000400578 - 0x0000000000400586 is .fini
0x0000000000400588 - 0x000000000040058c is .rodata
0x000000000040058c - 0x00000000004005b0 is .eh_frame_hdr
0x00000000004005b0 - 0x000000000040062c is .eh_frame
0x0000000000600630 - 0x0000000000600640 is .ctors
0x0000000000600640 - 0x0000000000600650 is .dtors
0x0000000000600650 - 0x0000000000600658 is .jcr
0x0000000000600658 - 0x00000000006007f8 is .dynamic
0x00000000006007f8 - 0x0000000000600800 is .got
0x0000000000600800 - 0x0000000000600820 is .got.plt
0x0000000000600820 - 0x0000000000600830 is .data
0x0000000000600830 - 0x0000000000600840 is .bss
// blah blah ....
So the only penalty is that you need extra disk space to store this
information.
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