Bug 532660 – sys-devel/gdb-7.7.1 - strange printing of a number in a string

• Product: Gentoo Linux
• Status: RESOLVED INVALID

[Description georg 2014-12-15 19:46:28 UTC]

The printing of variables inside gdb is sometimes very ugly.

Reproducible: Always

Steps to Reproduce:
1. compile attached program (gcc main.c -g -O0 -o test)
2. attach debugger (gdb test)
3. run until you pass the sprintf line
4. print v and buffer
Actual Results:  
 print v
$1 = 5.4000000000000004
print buffer
$2 = "5.40000000\000\377\377\177\000\000\230\221\244\367\377\177\000\000X\246\377\367\377\177\000\000H\341\377\367\377\177\000\000\000\000\000\000\000\000\000\000\001\000\000\000\000\000\000\000\375\006@\000\000\000\000\000\377\262\360", '\000' <repeats 13 times>, "\260\006@\000\000\000\000\000\020\005@\000\000\000\000\000`\340\377\377"


Expected Results:  
 print v
$1 = 5.4000000000000004
 print buffer
$2 = 5.40000000

It seems to be related to the pretty printing code.

[Comment 1 georg 2014-12-15 19:46:54 UTC]

Created attachment 391786 [details]
test source code

[Comment 2 georg 2014-12-15 19:48:24 UTC]

Created attachment 391788 [details]
gdb emerge info

[Comment 3 georg 2014-12-15 19:50:39 UTC]

I am uncertain if this is a bug which should be reported upstream or if it is related to some patch from gentoo ...

[Comment 4 georg 2014-12-15 20:00:07 UTC]

I got aware of such issue as i debugged some c++ application. See this snippet.

[INFO ] mgr::impl::check_create_config: int_config exists
[DEBUG] set sql: INSERT INTO myStructType (id, val1, val2, number, name) values ('100', '3.3999999999999999', '5.5999999999999996', '42', 'Georg')

Breakpoint 2, base::entity::mgr::impl::set (this=0x628d60, id=100, name="myStructType", desc=std::vector of length 4, capacity 4 = {...}, fnames=std::vector of length 4, capacity 4 = {...}, 
    values=std::vector of length 4, capacity 4 = {...}) at /home/georg/Dokumente/Entwicklung/misc/Comp/src/base/entity-mgr.cpp:201
201             char* err;
(gdb) print sql
$1 = "INSERT INTO myStructType (id, val1, val2, number, name) values ('100', '3.3", '9' <repeats 15 times>, "', '5.5", '9' <repeats 14 times>, "6', '42', 'Georg')"

I got
print sql
$1 = "INSERT INTO myStructType (id, val1, val2, number, name) values ('100', '3.3", '9' <repeats 15 times>, "', '5.5", '9' <repeats 14 times>, "6', '42', 'Georg')"

I expected
print sql
$1 = "INSERT INTO myStructType (id, val1, val2, number, name) values ('100', '3.3999999999999999', '5.5999999999999996', '42', 'Georg')"

[Comment 5 SpanKY 2015-02-20 15:49:21 UTC]

it's a fixed size buffer, so gdb prints out the whole thing.  if you cast it to a pointer w/out a size, it displays as you expect:
(gdb) print (char *)buffer
$4 = 0x7fffffffcb10 "5.40000000"

there might be some option controlling this behavior, but i'd have to read the manual to find out