Hi!
I have the following code snippet
char nf= *null_flags;
char r1nf= *(null_flags + s->rec_buff_length);
int eq= nf==r1nf;
fprintf(stderr, "man compare: %x\n", eq);
fprintf(stderr, "byte compare: %d\n",
(char)((char)*(char*)(null_flags)) == (char)(*(char*)(null_flags +
s->rec_buff_length)));
fprintf(stderr, "memcmp compare: %d\n", memcmp(null_flags ,
null_flags + s->rec_buff_length, 1));
Where the first printf (and the code leading to it) runs fine. No
problem at all.
The second and third printf calls here get a valgrind warning.
First printf:
==18960== Use of uninitialised value of size 8
==18960== at 0x792485B: _itoa_word (_itoa.c:195)
==18960== by 0x7926474: vfprintf (vfprintf.c:1600)
==18960== by 0x792A19F: buffered_vfprintf (vfprintf.c:2241)
==18960== by 0x7924FAD: vfprintf (vfprintf.c:1306)
==18960== by 0x792FB47: fprintf (fprintf.c:33)
==18960== by 0x5C3953: Table::compare_record() (table.cc:3522)
==18960== by 0x55CAFC: write_record(Session*, Table*,
st_copy_info*) (sql_insert.cc:846)
==18960== Conditional jump or move depends on uninitialised value(s)
==18960== at 0x7924865: _itoa_word (_itoa.c:195)
==18960== by 0x7926474: vfprintf (vfprintf.c:1600)
==18960== by 0x792A19F: buffered_vfprintf (vfprintf.c:2241)
==18960== by 0x7924FAD: vfprintf (vfprintf.c:1306)
==18960== by 0x792FB47: fprintf (fprintf.c:33)
==18960== by 0x5C3953: Table::compare_record() (table.cc:3522)
And the second in the memcmp() call (which if i copy the valgrind
implementation in, it gets the warning on the if(res) line of it:
res = ((int)a0) - ((int)b0); \
-->> if (res != 0) \
return res; \
I've disassembled both parts, and it looks correct (although perhaps
I'm wrong, help welcome)
leading up to first printf:
90 nop
48 8b 45 d8 mov -0x28(%rbp),%rax
48 8b 80 e0 00 00 00 mov 0xe0(%rax),%rax
0f b6 00 movzbl (%rax),%eax
88 45 ff mov %al,-0x1(%rbp)
48 8b 45 d8 mov -0x28(%rbp),%rax
48 8b 90 e0 00 00 00 mov 0xe0(%rax),%rdx
48 8b 45 d8 mov -0x28(%rbp),%rax
48 8b 00 mov (%rax),%rax
8b 80 24 02 00 00 mov 0x224(%rax),%eax
89 c0 mov %eax,%eax
48 8d 04 02 lea (%rdx,%rax,1),%rax
0f b6 00 movzbl (%rax),%eax
88 45 fe mov %al,-0x2(%rbp)
0f b6 45 ff movzbl -0x1(%rbp),%eax
3a 45 fe cmp -0x2(%rbp),%al
0f 94 c0 sete %al
0f b6 c0 movzbl %al,%eax
89 45 f0 mov %eax,-0x10(%rbp)
48 8b 05 ef 6b 62 00 mov 0x626bef(%rip),%rax # bf86f8
<stderr>
8b 55 f0 mov -0x10(%rbp),%edx
be d5 d1 8b 00 mov $0x8bd1d5,%esi
48 89 c7 mov %rax,%rdi
b8 00 00 00 00 mov $0x0,%eax
e8 12 10 42 00 callq 9f2b30 <fpri...@plt>
for the 2nd:
48 8b 45 d8 mov -0x28(%rbp),%rax
48 8b 80 e0 00 00 00 mov 0xe0(%rax),%rax
0f b6 10 movzbl (%rax),%edx
48 8b 45 d8 mov -0x28(%rbp),%rax
48 8b 80 98 00 00 00 mov 0x98(%rax),%rax
0f b6 00 movzbl (%rax),%eax
38 c2 cmp %al,%dl
0f 94 c0 sete %al
0f b6 d0 movzbl %al,%edx
48 8b 05 ae 6b 62 00 mov 0x626bae(%rip),%rax # bf86f8
<stderr>
be e6 d1 8b 00 mov $0x8bd1e6,%esi
48 89 c7 mov %rax,%rdi
b8 00 00 00 00 mov $0x0,%eax
e8 d4 0f 42 00 callq 9f2b30 <fpri...@plt>
So I'm a bit stuck... at first I thought we could in fact have
unitialized data... but doing the manual compare there (the first one)
and not getting a warning as well as inspecting the code and memory
contents for sanity, I'm quite stuck.
There has been no difference between gcc 4.3 and 4.4 nor between
valgrind 3.5 and trunk.
Does anybody have any ideas on what I can look at next? or tips on
debugging valgrind? perhaps tracking back as to exactly which operand
to what instruction it's complaining about? or if can get it to warn earlier?
--
Stewart Smith
------------------------------------------------------------------------------
Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day
trial. Simplify your report design, integration and deployment - and focus on
what you do best, core application coding. Discover what's new with
Crystal Reports now. http://p.sf.net/sfu/bobj-july
_______________________________________________
Valgrind-users mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/valgrind-users
