gdb unable to print fn argument correctly

[Manoj Iyer <manjo at austin dot ibm dot com>]

I have an test program which has a function of the nature 'void fn(double
c){}', which is compiled as a PwerPC 64bit application. When I set a
breakpoint and stop on this function, GDB is not printing the arguments
passed to this function correctly.

I did some initial debugging, the dwarf information and dissassembly of
the function looks good to me. But I am not able to pin point who is
corrupting the stack. I believe gdb is just printing what is avaiable in
the stack to output.

Any pointers to help me identify the culprit deeply appreciated.


============= test.c ========================

#include <stdio.h>

void fn1(int a) {}
void fn2(long b){}
void fn3(double c){}

int
main()
{
    fn1(1234);
    fn2(123456789L);
    fn3(1234.4567);
    return 0;
}
============= end test.c ======================

============= GDB output ======================
(gdb) br main
Breakpoint 1 at 0x10000574: file /tmp/test1.c, line 10.
(gdb) br fn3
Breakpoint 2 at 0x10000544: file /tmp/test1.c, line 5.
(gdb) r
Starting program: /tmp/test.gdb

Breakpoint 1, main () at /tmp/test1.c:10
10          fn1(1234);
(gdb) c
Continuing.

Breakpoint 2, 0x0000000010000544 in fn3 (c=6.0995758190771502e-316)
    at /tmp/test1.c:5
5       void fn3(double c){}
(gdb)

================= end gdb output ==========================

When I change this testcase, change function fn3 to have something
meaningful in the body, gdb prints the arguments correctly.

=================== modified test.c ======================
#include <stdio.h>

void fn1(int a) {}
void fn2(long b){}
void fn3(double c){printf("hello world %lf\n", c);}

int
main()
{
    fn1(1234);
    fn2(123456789L);
    fn3(1234.4567);
    return 0;
}

================= end of test.c ==========================

================= output from gdb =======================
(gdb) br main
Breakpoint 1 at 0x100004c0: file test.c, line 9.
(gdb) br fn3
Breakpoint 2 at 0x10000488: file test.c, line 5.
(gdb) r
Starting program: /tmp/test

Breakpoint 1, main () at test.c:9
warning: Source file is more recent than executable.

9           fn1(1234);
(gdb) c
Continuing.

Breakpoint 2, fn3 (c=1234.4567) at test.c:5
5       void fn3(double c){printf("hello world %lf\n", c);}
(gdb)

================== end of output from gdb ===================

=================== DWARF info for fn3() ===================
 <1><2bf>: Abbrev Number: 4 (DW_TAG_subprogram)
     DW_AT_sibling     : <2e3>
     DW_AT_external    : 1
     DW_AT_name        : fn3
     DW_AT_decl_file   : 1
     DW_AT_decl_line   : 5
     DW_AT_prototyped  : 1
     DW_AT_low_pc      : 0x10000448 268436552
     DW_AT_high_pc     : 0x10000468 268436584
     DW_AT_frame_base  : 1 byte block: 6f       (DW_OP_reg31)
 <2><2d6>: Abbrev Number: 5 (DW_TAG_formal_parameter)
     DW_AT_name        : c
     DW_AT_decl_file   : 1
     DW_AT_decl_line   : 5
     DW_AT_type        : <2e3>
     DW_AT_location    : 2 byte block: 91 8     (DW_OP_fbreg: 8)
 <1><2e3>: Abbrev Number: 3 (DW_TAG_base_type)
     DW_AT_name        : double
     DW_AT_byte_size   : 8
     DW_AT_encoding    : 4      (float)
=================================================================

==== Disassembly of void fn3(double c){} =======================
fn3()
[5]     10000448:   94 21 ff e0   stwu       r1, -32(r1)
        1000044c:   93 e1 00 1c   stw        r31, 28(r1)
        10000450:   7c 3f 0b 78   mr         r31, r1
        10000454:   d8 3f 00 08   stfd       fr1, 8(r31)
        10000458:   81 61 00 00   lwz        r11, 0(r1)
        1000045c:   83 eb ff fc   lwz        r31, -4(r11)
        10000460:   7d 61 5b 78   mr         r1, r11
        10000464:   4e 80 00 20   blr
==================================================================

Thanks
-----
manjo
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+ Cogito ergo sum                                                          +
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