Take the following trivial program:
#include <iostream>int main() { return 0;}If I run this using valgrind, I'm told that there are 72,704 bytes in 1 blocks that are still reachable. There have been extensive discussions on SO about whether or not to worry about still reachable warnings--I'm not concerned about that. I'd just like to understand how simply including a standard library header could cause a still reachable warning, when none of the objects from that library were allocated in the program itself.
Here is the full valgrind output:
$ valgrind --leak-check=full --track-origins=yes --show-reachable=yes ./ValgrindTest==27671== Memcheck, a memory error detector==27671== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.==27671== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info==27671== Command: ./ValgrindTest==27671== ==27671== ==27671== HEAP SUMMARY:==27671== in use at exit: 72,704 bytes in 1 blocks==27671== total heap usage: 1 allocs, 0 frees, 72,704 bytes allocated==27671== ==27671== 72,704 bytes in 1 blocks are still reachable in loss record 1 of 1==27671== at 0x4C2AB9D: malloc (vg_replace_malloc.c:296)==27671== by 0x4EC060F: ??? (in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.21)==27671== by 0x400F305: call_init.part.0 (dl-init.c:85)==27671== by 0x400F3DE: call_init (dl-init.c:52)==27671== by 0x400F3DE: _dl_init (dl-init.c:134)==27671== by 0x40016E9: ??? (in /lib/x86_64-linux-gnu/ld-2.15.so)==27671== ==27671== LEAK SUMMARY:==27671== definitely lost: 0 bytes in 0 blocks==27671== indirectly lost: 0 bytes in 0 blocks==27671== possibly lost: 0 bytes in 0 blocks==27671== still reachable: 72,704 bytes in 1 blocks==27671== suppressed: 0 bytes in 0 blocks==27671== ==27671== For counts of detected and suppressed errors, rerun with: -v==27671== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)And an object dump:
$ objdump -d ValgrindTest ValgrindTest: file format elf64-x86-64Disassembly of section .init:0000000000400718 <_init>: 400718: 48 83 ec 08 sub $0x8,%rsp 40071c: e8 8b 00 00 00 callq 4007ac <call_gmon_start> 400721: 48 83 c4 08 add $0x8,%rsp 400725: c3 retq Disassembly of section .plt:0000000000400730 <_ZNSt8ios_base4InitC1Ev@plt-0x10>: 400730: ff 35 ba 08 20 00 pushq 0x2008ba(%rip) # 600ff0 <_GLOBAL_OFFSET_TABLE_+0x8> 400736: ff 25 bc 08 20 00 jmpq *0x2008bc(%rip) # 600ff8 <_GLOBAL_OFFSET_TABLE_+0x10> 40073c: 0f 1f 40 00 nopl 0x0(%rax)0000000000400740 <_ZNSt8ios_base4InitC1Ev@plt>: 400740: ff 25 ba 08 20 00 jmpq *0x2008ba(%rip) # 601000 <_GLOBAL_OFFSET_TABLE_+0x18> 400746: 68 00 00 00 00 pushq $0x0 40074b: e9 e0 ff ff ff jmpq 400730 <_init+0x18>0000000000400750 <__libc_start_main@plt>: 400750: ff 25 b2 08 20 00 jmpq *0x2008b2(%rip) # 601008 <_GLOBAL_OFFSET_TABLE_+0x20> 400756: 68 01 00 00 00 pushq $0x1 40075b: e9 d0 ff ff ff jmpq 400730 <_init+0x18>0000000000400760 <__cxa_atexit@plt>: 400760: ff 25 aa 08 20 00 jmpq *0x2008aa(%rip) # 601010 <_GLOBAL_OFFSET_TABLE_+0x28> 400766: 68 02 00 00 00 pushq $0x2 40076b: e9 c0 ff ff ff jmpq 400730 <_init+0x18>0000000000400770 <_ZNSt8ios_base4InitD1Ev@plt>: 400770: ff 25 a2 08 20 00 jmpq *0x2008a2(%rip) # 601018 <_GLOBAL_OFFSET_TABLE_+0x30> 400776: 68 03 00 00 00 pushq $0x3 40077b: e9 b0 ff ff ff jmpq 400730 <_init+0x18>Disassembly of section .text:0000000000400780 <_start>: 400780: 31 ed xor %ebp,%ebp 400782: 49 89 d1 mov %rdx,%r9 400785: 5e pop %rsi 400786: 48 89 e2 mov %rsp,%rdx 400789: 48 83 e4 f0 and $0xfffffffffffffff0,%rsp 40078d: 50 push %rax 40078e: 54 push %rsp 40078f: 49 c7 c0 80 09 40 00 mov $0x400980,%r8 400796: 48 c7 c1 f0 08 40 00 mov $0x4008f0,%rcx 40079d: 48 c7 c7 90 08 40 00 mov $0x400890,%rdi 4007a4: e8 a7 ff ff ff callq 400750 <__libc_start_main@plt> 4007a9: f4 hlt 4007aa: 90 nop 4007ab: 90 nop00000000004007ac <call_gmon_start>: 4007ac: 48 83 ec 08 sub $0x8,%rsp 4007b0: 48 8b 05 29 08 20 00 mov 0x200829(%rip),%rax # 600fe0 <_DYNAMIC+0x1f0> 4007b7: 48 85 c0 test %rax,%rax 4007ba: 74 02 je 4007be <call_gmon_start+0x12> 4007bc: ff d0 callq *%rax 4007be: 48 83 c4 08 add $0x8,%rsp 4007c2: c3 retq 4007c3: 90 nop 4007c4: 90 nop 4007c5: 90 nop 4007c6: 90 nop 4007c7: 90 nop 4007c8: 90 nop 4007c9: 90 nop 4007ca: 90 nop 4007cb: 90 nop 4007cc: 90 nop 4007cd: 90 nop 4007ce: 90 nop 4007cf: 90 nop00000000004007d0 <deregister_tm_clones>: 4007d0: b8 37 10 60 00 mov $0x601037,%eax 4007d5: 55 push %rbp 4007d6: 48 2d 30 10 60 00 sub $0x601030,%rax 4007dc: 48 83 f8 0e cmp $0xe,%rax 4007e0: 48 89 e5 mov %rsp,%rbp 4007e3: 77 02 ja 4007e7 <deregister_tm_clones+0x17> 4007e5: 5d pop %rbp 4007e6: c3 retq 4007e7: b8 00 00 00 00 mov $0x0,%eax 4007ec: 48 85 c0 test %rax,%rax 4007ef: 74 f4 je 4007e5 <deregister_tm_clones+0x15> 4007f1: 5d pop %rbp 4007f2: bf 30 10 60 00 mov $0x601030,%edi 4007f7: ff e0 jmpq *%rax 4007f9: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)0000000000400800 <register_tm_clones>: 400800: b8 30 10 60 00 mov $0x601030,%eax 400805: 55 push %rbp 400806: 48 2d 30 10 60 00 sub $0x601030,%rax 40080c: 48 c1 f8 03 sar $0x3,%rax 400810: 48 89 e5 mov %rsp,%rbp 400813: 48 89 c2 mov %rax,%rdx 400816: 48 c1 ea 3f shr $0x3f,%rdx 40081a: 48 01 d0 add %rdx,%rax 40081d: 48 d1 f8 sar %rax 400820: 75 02 jne 400824 <register_tm_clones+0x24> 400822: 5d pop %rbp 400823: c3 retq 400824: ba 00 00 00 00 mov $0x0,%edx 400829: 48 85 d2 test %rdx,%rdx 40082c: 74 f4 je 400822 <register_tm_clones+0x22> 40082e: 5d pop %rbp 40082f: 48 89 c6 mov %rax,%rsi 400832: bf 30 10 60 00 mov $0x601030,%edi 400837: ff e2 jmpq *%rdx 400839: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)0000000000400840 <__do_global_dtors_aux>: 400840: 80 3d e9 07 20 00 00 cmpb $0x0,0x2007e9(%rip) # 601030 <__bss_start> 400847: 75 11 jne 40085a <__do_global_dtors_aux+0x1a> 400849: 55 push %rbp 40084a: 48 89 e5 mov %rsp,%rbp 40084d: e8 7e ff ff ff callq 4007d0 <deregister_tm_clones> 400852: 5d pop %rbp 400853: c6 05 d6 07 20 00 01 movb $0x1,0x2007d6(%rip) # 601030 <__bss_start> 40085a: f3 c3 repz retq 40085c: 0f 1f 40 00 nopl 0x0(%rax)0000000000400860 <frame_dummy>: 400860: 48 83 3d 80 05 20 00 cmpq $0x0,0x200580(%rip) # 600de8 <__JCR_END__> 400867: 00 400868: 74 1e je 400888 <frame_dummy+0x28> 40086a: b8 00 00 00 00 mov $0x0,%eax 40086f: 48 85 c0 test %rax,%rax 400872: 74 14 je 400888 <frame_dummy+0x28> 400874: 55 push %rbp 400875: bf e8 0d 60 00 mov $0x600de8,%edi 40087a: 48 89 e5 mov %rsp,%rbp 40087d: ff d0 callq *%rax 40087f: 5d pop %rbp 400880: e9 7b ff ff ff jmpq 400800 <register_tm_clones> 400885: 0f 1f 00 nopl (%rax) 400888: e9 73 ff ff ff jmpq 400800 <register_tm_clones> 40088d: 90 nop 40088e: 90 nop 40088f: 90 nop0000000000400890 <main>: 400890: 55 push %rbp 400891: 48 89 e5 mov %rsp,%rbp 400894: b8 00 00 00 00 mov $0x0,%eax 400899: 5d pop %rbp 40089a: c3 retq 000000000040089b <_Z41__static_initialization_and_destruction_0ii>: 40089b: 55 push %rbp 40089c: 48 89 e5 mov %rsp,%rbp 40089f: 48 83 ec 10 sub $0x10,%rsp 4008a3: 89 7d fc mov %edi,-0x4(%rbp) 4008a6: 89 75 f8 mov %esi,-0x8(%rbp) 4008a9: 83 7d fc 01 cmpl $0x1,-0x4(%rbp) 4008ad: 75 27 jne 4008d6 <_Z41__static_initialization_and_destruction_0ii+0x3b> 4008af: 81 7d f8 ff ff 00 00 cmpl $0xffff,-0x8(%rbp) 4008b6: 75 1e jne 4008d6 <_Z41__static_initialization_and_destruction_0ii+0x3b> 4008b8: bf 34 10 60 00 mov $0x601034,%edi 4008bd: e8 7e fe ff ff callq 400740 <_ZNSt8ios_base4InitC1Ev@plt> 4008c2: ba 28 10 60 00 mov $0x601028,%edx 4008c7: be 34 10 60 00 mov $0x601034,%esi 4008cc: bf 70 07 40 00 mov $0x400770,%edi 4008d1: e8 8a fe ff ff callq 400760 <__cxa_atexit@plt> 4008d6: c9 leaveq 4008d7: c3 retq 00000000004008d8 <_GLOBAL__sub_I_main>: 4008d8: 55 push %rbp 4008d9: 48 89 e5 mov %rsp,%rbp 4008dc: be ff ff 00 00 mov $0xffff,%esi 4008e1: bf 01 00 00 00 mov $0x1,%edi 4008e6: e8 b0 ff ff ff callq 40089b <_Z41__static_initialization_and_destruction_0ii> 4008eb: 5d pop %rbp 4008ec: c3 retq 4008ed: 90 nop 4008ee: 90 nop 4008ef: 90 nop00000000004008f0 <__libc_csu_init>: 4008f0: 48 89 6c 24 d8 mov %rbp,-0x28(%rsp) 4008f5: 4c 89 64 24 e0 mov %r12,-0x20(%rsp) 4008fa: 48 8d 2d df 04 20 00 lea 0x2004df(%rip),%rbp # 600de0 <__init_array_end> 400901: 4c 8d 25 c8 04 20 00 lea 0x2004c8(%rip),%r12 # 600dd0 <__frame_dummy_init_array_entry> 400908: 4c 89 6c 24 e8 mov %r13,-0x18(%rsp) 40090d: 4c 89 74 24 f0 mov %r14,-0x10(%rsp) 400912: 4c 89 7c 24 f8 mov %r15,-0x8(%rsp) 400917: 48 89 5c 24 d0 mov %rbx,-0x30(%rsp) 40091c: 48 83 ec 38 sub $0x38,%rsp 400920: 4c 29 e5 sub %r12,%rbp 400923: 41 89 fd mov %edi,%r13d 400926: 49 89 f6 mov %rsi,%r14 400929: 48 c1 fd 03 sar $0x3,%rbp 40092d: 49 89 d7 mov %rdx,%r15 400930: e8 e3 fd ff ff callq 400718 <_init> 400935: 48 85 ed test %rbp,%rbp 400938: 74 1c je 400956 <__libc_csu_init+0x66> 40093a: 31 db xor %ebx,%ebx 40093c: 0f 1f 40 00 nopl 0x0(%rax) 400940: 4c 89 fa mov %r15,%rdx 400943: 4c 89 f6 mov %r14,%rsi 400946: 44 89 ef mov %r13d,%edi 400949: 41 ff 14 dc callq *(%r12,%rbx,8) 40094d: 48 83 c3 01 add $0x1,%rbx 400951: 48 39 eb cmp %rbp,%rbx 400954: 75 ea jne 400940 <__libc_csu_init+0x50> 400956: 48 8b 5c 24 08 mov 0x8(%rsp),%rbx 40095b: 48 8b 6c 24 10 mov 0x10(%rsp),%rbp 400960: 4c 8b 64 24 18 mov 0x18(%rsp),%r12 400965: 4c 8b 6c 24 20 mov 0x20(%rsp),%r13 40096a: 4c 8b 74 24 28 mov 0x28(%rsp),%r14 40096f: 4c 8b 7c 24 30 mov 0x30(%rsp),%r15 400974: 48 83 c4 38 add $0x38,%rsp 400978: c3 retq 400979: 0f 1f 80 00 00 00 00 nopl 0x0(%rax)0000000000400980 <__libc_csu_fini>: 400980: f3 c3 repz retq 400982: 90 nop 400983: 90 nopDisassembly of section .fini:0000000000400984 <_fini>: 400984: 48 83 ec 08 sub $0x8,%rsp 400988: 48 83 c4 08 add $0x8,%rsp 40098c: c3 retq For completeness, I'm using:
Ubuntu: 12.04
Valgrind: 3.10.1 3.7.0
g++: 4.8.1
NB: As a side note, this does not happen when I include other headers such as <fstream> or <cmath>.