[Bug gdb/18436] Can't print dynamically allocated global array

["stanton at haas dot berkeley.edu" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=18436

--- Comment #7 from stanton at haas dot berkeley.edu ---
Thanks, Keith. I found a port of readelf, but it doesn’t like my executable:

Richards-Mac-Pro:C stanton$ greadelf -w main | grep producer
readelf: Error: Not an ELF file - it has the wrong magic bytes at the start

> On May 20, 2015, at 10:48 AM, keiths at redhat dot com <sourceware-bugzilla@sourceware.org> wrote:
> 
> https://sourceware.org/bugzilla/show_bug.cgi?id=18436
> 
> --- Comment #5 from Keith Seitz <keiths at redhat dot com> ---
> (In reply to stanton from comment #2)
>> Thanks for the response, Keith First, I’m running OS X 10.10.3.
>> 
>> Test 1: MacPorts versions of gdb and gcc
>> gdb version = GNU gdb (GDB) 7.7.1
>> gcc version = gcc version 4.9.2 (MacPorts gcc49 4.9.2_1) 
>> 
>> (gdb) print vec[0]
>> cannot subscript something of type `<data variable, no debug info>'
>> (gdb) info var ^vec$
>> All variables matching regular expression "^vec$":
>> 
>> Non-debugging symbols:
>> 0x0000000100001028  vec
>> 
> 
> Considering you have source files and can step through your program, this tells
> me that there is a debug info problem concerning the global variable vec or
> there is some obscure bug in gdb preventing this from working.
> 
> I have some vague recollection of custom Apple DWARF extensions making their
> way into GCC for MacOS, but not GDB. That might explain why LLDB can
> successfully inspect the variable.
> 
> Does "readelf -w" (does that exist on Mac?) show any output DIEs?
> 
> For example, for the test case associated with this bug,
> 
> $ readelf -w main | grep producer
>     <c>   DW_AT_producer    : (indirect string, offset: 0xb6): GNU C 4.9.2
> 20150212 (Red Hat 4.9.2-6) -mtune=generic -march=x86-64 -g  
>    DW_AT_producer     DW_FORM_strp
> 
> Other than the fact that we have debug DIEs, we can also see the "-g" was
> passed to GCC to output debug info.
> 
> Also, what is the debug info for "vec" (if any)? In my build of the test, I
> have:
> <1><d7>: Abbrev Number: 8 (DW_TAG_variable)
>    <d8>   DW_AT_name        : vec      
>    <dc>   DW_AT_decl_file   : 1        
>    <dd>   DW_AT_decl_line   : 4        
>    <de>   DW_AT_type        : <0xec>   
>    <e2>   DW_AT_external    : 1        
>    <e2>   DW_AT_location    : 9 byte block: 3 50 10 60 0 0 0 0 0      
> (DW_OP_addr: 601050)
> 
> A (not satisfactory IMO) workaround is to tell gdb what "vec" is:
> (gdb) file ~/tmp/18436.nodebug
> (gdb) start
> Temporary breakpoint 1 at 0x4005ca
> Starting program: /home/keiths/tmp/18436.nodebug 
> 
> Temporary breakpoint 1, 0x00000000004005ca in main ()
> (gdb) ni 50
> Item 0 =               0
> 0x000000000040062b in main ()
> (gdb) p vec[0]
> cannot subscript something of type `<data variable, no debug info>'
> (gdb) p ((double*)vec)[0]
> $1 = 0
> (gdb)
> 
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From: "stanton at haas dot berkeley.edu" <sourceware-bugzilla@sourceware.org>
To: gdb-prs@sourceware.org
Subject: [Bug gdb/18436] Can't print dynamically allocated global array
Date: Wed, 20 May 2015 18:18:00 -0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=18436

--- Comment #8 from stanton at haas dot berkeley.edu ---
Unfortunately, the workaround below doesn’t work on my system:

(gdb) print vec[0]
cannot subscript something of type `<data variable, no debug info>'
(gdb) print ((double*)vec)[0]
Cannot access memory at address 0x200000

I just installed MacPorts gcc 5.1.0, and also hand-compiled gdb 7.9.1. It
didn’t help.

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From: "stanton at haas dot berkeley.edu" <sourceware-bugzilla@sourceware.org>
To: gdb-prs@sourceware.org
Subject: [Bug gdb/18436] Can't print dynamically allocated global array
Date: Wed, 20 May 2015 20:16:00 -0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=18436

--- Comment #9 from stanton at haas dot berkeley.edu ---
I just noticed something odd. Using gcc 5.1 and gdb 7.7.1 (both MacPorts), I
can inspect v[0] fine if I compile like this:

gcc -g main.c -o main

It fails if I compile the same program (same gcc, some gdb) like this:

gcc -g -c -o main.o main.c
gcc -o main main.o 

Any idea why this should be different? 


> On May 20, 2015, at 11:17 AM, Richard Stanton <stanton@haas.berkeley.edu> wrote:
> 
> Unfortunately, the workaround below doesn’t work on my system:
> 
> (gdb) print vec[0]
> cannot subscript something of type `<data variable, no debug info>'
> (gdb) print ((double*)vec)[0]
> Cannot access memory at address 0x200000
> 
> I just installed MacPorts gcc 5.1.0, and also hand-compiled gdb 7.9.1. It didn’t help.
> 
>

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From: "dje at google dot com" <sourceware-bugzilla@sourceware.org>
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Subject: [Bug python/11324] python pretty-printers uglify backtraces
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https://sourceware.org/bugzilla/show_bug.cgi?id\x11324

dje at google dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |dje at google dot com
         Resolution|---                         |FIXED

--- Comment #2 from dje at google dot com ---
IIUC the intended solution is now implemented: gdbpy_gdb_memory_error and
print_stack_unless_memory_error.

Please reopen and clarify if not.

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