How do I write a loop in a gdb script?

Question

After adapting this answer, I wrote the following loop to simply print an array in gdb in a script called "gdb_script.gs". What am I doing wrong?

set $end=64  
while ($i<$end)
   print $i
   print volfrac($i, :, 1)
   set $i=$i+1
end

where volfrac(:,:,:) is a fortran array. I am getting the error:

 gdb_script.gs:14: Error in sourced command file:
 A syntax error in expression, near `<$end)'.

Don't you want to initialize `$i` before comparing it to anything? — Employed Russian, Sep 28 '17 at 02:19

score 12 · Accepted Answer · answered Apr 05 '18 at 14:53

The other answer totally missed the point. The hint was the reported error:

    gdb_script.gs:14: Error in sourced command file:
    A syntax error in expression, near `<$end)'.

The hint is <$end), which means there is a syntax error in the while statement. By experimenting further, I am posting my results if others need it in the future:

 set $ipx=0
 set $end=32

 while ($ipx .lt. 32)
     print $ipx
     print ro($ipx, 1)
     set $ipx=$ipx+1
 end

The key was to use the fortran syntax for comparison ($ipx .lt. 32) instead of the usual "c" syntax ($ipx < 32).

score 4 · Answer 2 · edited Nov 07 '19 at 17:01

4

GDB newbies (as myself) should know that the accepted answer does not work unless you remove the blank between while and the first brace.

Also, the .lt. syntax probably works only for Fortran (https://sourceware.org/gdb/current/onlinedocs/gdb/Fortran.html). As the title of the question is not formulated specifically toward Fortran developers, the accepted answer can be misleading.

edited Nov 07 '19 at 17:01

S.S. Anne

15,171
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answered Nov 07 '19 at 13:33

Nefira

77
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1

You should perhaps mention the GDB version you used. – Armali Nov 07 '19 at 13:57
Not in title but the text of the question does mention Fortran. Also when I was posting the question, I did not know gdb syntax depends on the language being debugged. – wander95 Nov 07 '19 at 17:56
1

@Armali, I am using GDB 7.7.1. – Nefira Nov 15 '19 at 13:06

score 3 · Answer 3 · answered Jan 06 '20 at 09:04

3

set $i = 0
p $i++

keep pressing Enter this is one of the easiest logic I found

answered Jan 06 '20 at 09:04

Ravi Kumar Yadav

193
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Irrelevant. You didn't read the question. I am trying to print an big Fortran array. If the array is 512x512x4 are you willing to press enter 262144x4 times ? See accepted answer – wander95 Jan 06 '20 at 14:59
1

this was helpful for my small use case, thank you – TheGaldozer May 06 '23 at 02:02

Peter Teoh · Answer 4 · 2017-10-13T13:29:46.943

Since voltrac() is an array, then I think it is a syntax error as show in your output - it should be "print volfrac[]" instead.

Below I showed you the step by step in detail for a C program (since you are working with gdb, and gdb only worked with ELF file, and so it is the same here - gdb + ELF file for C):

(gdb) run
Starting program: /home/tthtlc/a.out 

Breakpoint 1, main () at main.c:5
5 main(){

First I step through a few times and noticed my assignment:

(gdb) s
8     for(i=0;i<10;i++)
(gdb) 
9     for(j=0;j<10;j++)
(gdb) 
10        for(k=0;k<10;k++) {
(gdb) 
**11      volfrac[i][j][k]=0xdeadbeef;**
(gdb)

Now is the printing out (and notice the different ways of printing the array):

(gdb) print /x volfrac[0][0][0]
$5 = 0xdeadbeef
(gdb) print /x volfrac[0][0]
$6 = {0xdeadbeef, 0xdeadbeef, 0xdeadbeef, 0xdeadbeef, 0xdeadbeef, 0xdeadbeef, 
  0x0, 0x0, 0x0, 0x0}
(gdb) print /x volfrac[0]
$7 = {{0xdeadbeef, 0xdeadbeef, 0xdeadbeef, 0xdeadbeef, 0xdeadbeef, 0xdeadbeef, 
(gdb) print /x volfrac
$8 = {{{0xdeadbeef, 0xdeadbeef, 0xdeadbeef, 0xdeadbeef, 0xdeadbeef, 
      0xdeadbeef, 0x0, 0x0, 0x0, 0x0}, {0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 
(gdb) print /x volfrac(0,0,0)
Invalid data type for function to be called.

How do I write a loop in a gdb script?

4 Answers4

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