如果简单的linux c程序链接到自定义的glibc库，则出现分段错误

Question

I am using 64bit Ubuntu 14.04.5 LTS(kernel:4.4.0-31-generic). The gcc version is

gcc --version
gcc (Ubuntu 4.8.4-2ubuntu1~14.04.3) 4.8.4

I am new to linux c and glibc. I don't know much about the internal of linux c runtime.

I hava a very simple c code:

#include <stdio.h>
#include <stdlib.h>

int main()
{
    char *str = NULL;
    str = (char *)malloc(sizeof(char));
    *str = 'a';

    char *p = (char *)realloc(str, sizeof(char) * 10);
    if (p != NULL)
    {
        str = p;
    }

    printf("%s\n", str);

    return 0;
}

I compile the code using gcc and make it 32bit executable on the x64 linux.

VirtualBox:/software/code/c++workspace/kernel$ gcc -g -m32 -o malc malloc.c
VirtualBox:/software/code/c++workspace/kernel$ ./malc   #here output a. It's correct
a
VirtualBox:/software/code/c++workspace/kernel$ ldd malc
    linux-gate.so.1 =>  (0xf7712000)
    libc.so.6 => /lib/i386-linux-gnu/libc.so.6 (0xf7541000)
    /lib/ld-linux.so.2 (0x565d9000)

Here the demostration is just want to show that, if I use default lib on the OS, everything is fine.

I would like to learn some functions in the glibc, so I want to compile a debug x86 mode libc.so object, then make it linked to my code.

I first want to compile the glibc source code into 64bit mode, then try to link to my code to check if my compiled glibc can work or not on 64bit runtime.

I met the same issue when I try to compile the glibc into 32bit and 64bit. So the below steps are just show the output of trying to compile into 64bit.

My steps are: 1)

git clone git://sourceware.org/git/glibc.git
cd glibc
git checkout --track -b local_glibc-2.25 origin/release/2.25/master

2)

VirtualBox:/software/code/c++workspace/glibc_source$ ./glibc/configure --prefix=/software/code/c++workspace/glibc_bin_x64
VirtualBox:/software/code/c++workspace/glibc_source$ make
VirtualBox:/software/code/c++workspace/glibc_source$ make install

3)

 VirtualBox:/software/code/c++workspace/kernel$ gcc -g -O0 -v -da -Q -o malc malloc.c -Wl,-rpath /software/code/c++workspace/glibc_bin_x64/lib
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/4.8/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.8.4-2ubuntu1~14.04.3' --with-bugurl=file:///usr/share/doc/gcc-4.8/README.Bugs --enable-languages=c,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-4.8 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.8 --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --enable-gnu-unique-object --disable-libmudflap --enable-plugin --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.8-amd64 --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.8-amd64 --with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.8.4 (Ubuntu 4.8.4-2ubuntu1~14.04.3) 
COLLECT_GCC_OPTIONS='-g' '-O0' '-v' '-da' '-Q' '-o' 'malc' '-mtune=generic' '-march=x86-64'
 /usr/lib/gcc/x86_64-linux-gnu/4.8/cc1 -v -imultiarch x86_64-linux-gnu malloc.c -dumpbase malloc.c -da -mtune=generic -march=x86-64 -auxbase malloc -g -O0 -version -fstack-protector -Wformat -Wformat-security -o /tmp/ccREHRcN.s
GNU C (Ubuntu 4.8.4-2ubuntu1~14.04.3) version 4.8.4 (x86_64-linux-gnu)
    compiled by GNU C version 4.8.4, GMP version 5.1.3, MPFR version 3.1.2-p3, MPC version 1.0.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory "/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../x86_64-linux-gnu/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/x86_64-linux-gnu/4.8/include
 /usr/local/include
 /usr/lib/gcc/x86_64-linux-gnu/4.8/include-fixed
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.
GNU C (Ubuntu 4.8.4-2ubuntu1~14.04.3) version 4.8.4 (x86_64-linux-gnu)
    compiled by GNU C version 4.8.4, GMP version 5.1.3, MPFR version 3.1.2-p3, MPC version 1.0.1
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
options passed:  -v -imultiarch x86_64-linux-gnu malloc.c -mtune=generic
 -march=x86-64 -g -O0 -fstack-protector -Wformat -Wformat-security
options enabled:  -faggressive-loop-optimizations
 -fasynchronous-unwind-tables -fauto-inc-dec -fbranch-count-reg -fcommon
 -fdelete-null-pointer-checks -fdwarf2-cfi-asm -fearly-inlining
 -feliminate-unused-debug-types -ffunction-cse -fgcse-lm -fgnu-runtime
 -fgnu-unique -fident -finline-atomics -fira-hoist-pressure
 -fira-share-save-slots -fira-share-spill-slots -fivopts
 -fkeep-static-consts -fleading-underscore -fmath-errno
 -fmerge-debug-strings -fmove-loop-invariants -fpeephole
 -fprefetch-loop-arrays -freg-struct-return -fsched-critical-path-heuristic
 -fsched-dep-count-heuristic -fsched-group-heuristic -fsched-interblock
 -fsched-last-insn-heuristic -fsched-rank-heuristic -fsched-spec
 -fsched-spec-insn-heuristic -fsched-stalled-insns-dep -fshow-column
 -fsigned-zeros -fsplit-ivs-in-unroller -fstack-protector
 -fstrict-volatile-bitfields -fsync-libcalls -ftrapping-math
 -ftree-coalesce-vars -ftree-cselim -ftree-forwprop -ftree-loop-if-convert
 -ftree-loop-im -ftree-loop-ivcanon -ftree-loop-optimize
 -ftree-parallelize-loops= -ftree-phiprop -ftree-pta -ftree-reassoc
 -ftree-scev-cprop -ftree-slp-vectorize -ftree-vect-loop-version
 -funit-at-a-time -funwind-tables -fvar-tracking -fvar-tracking-assignments
 -fzero-initialized-in-bss -m128bit-long-double -m64 -m80387
 -maccumulate-outgoing-args -malign-stringops -mfancy-math-387
 -mfp-ret-in-387 -mfxsr -mglibc -mieee-fp -mlong-double-80 -mmmx -mno-sse4
 -mpush-args -mred-zone -msse -msse2 -mtls-direct-seg-refs
Compiler executable checksum: a0a649d344b1ed798e33d30772d46437
 __bswap_32 __bswap_64 main
Analyzing compilation unit
Performing interprocedural optimizations
 <*free_lang_data> <visibility> <early_local_cleanups> <*free_inline_summary> <whole-program>Assembling functions:
 main
Execution times (seconds)
 phase setup             :   0.00 ( 0%) usr   0.00 ( 0%) sys   0.01 (20%) wall    1106 kB (50%) ggc
 phase parsing           :   0.01 (50%) usr   0.02 (100%) sys   0.03 (60%) wall    1027 kB (47%) ggc
 phase opt and generate  :   0.01 (50%) usr   0.00 ( 0%) sys   0.01 (20%) wall      44 kB ( 2%) ggc
 callgraph optimization  :   0.01 (50%) usr   0.00 ( 0%) sys   0.00 ( 0%) wall       1 kB ( 0%) ggc
 preprocessing           :   0.00 ( 0%) usr   0.00 ( 0%) sys   0.03 (60%) wall     326 kB (15%) ggc
 lexical analysis        :   0.01 (50%) usr   0.00 ( 0%) sys   0.00 ( 0%) wall       0 kB ( 0%) ggc
 parser (global)         :   0.00 ( 0%) usr   0.01 (50%) sys   0.00 ( 0%) wall     483 kB (22%) ggc
 parser enumerator list  :   0.00 ( 0%) usr   0.01 (50%) sys   0.00 ( 0%) wall       2 kB ( 0%) ggc
 rest of compilation     :   0.00 ( 0%) usr   0.00 ( 0%) sys   0.01 (20%) wall       2 kB ( 0%) ggc
 TOTAL                 :   0.02             0.02             0.05               2197 kB
COLLECT_GCC_OPTIONS='-g' '-O0' '-v' '-da' '-Q' '-o' 'malc' '-mtune=generic' '-march=x86-64'
 as -v --64 -o /tmp/cc8sf3O6.o /tmp/ccREHRcN.s
GNU assembler version 2.24 (x86_64-linux-gnu) using BFD version (GNU Binutils for Ubuntu) 2.24
COMPILER_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.8/:/usr/lib/gcc/x86_64-linux-gnu/4.8/:/usr/lib/gcc/x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.8/:/usr/lib/gcc/x86_64-linux-gnu/
LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/4.8/:/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/:/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib/:/lib/x86_64-linux-gnu/:/lib/../lib/:/usr/lib/x86_64-linux-gnu/:/usr/lib/../lib/:/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../:/lib/:/usr/lib/
COLLECT_GCC_OPTIONS='-g' '-O0' '-v' '-da' '-Q' '-o' 'malc' '-mtune=generic' '-march=x86-64'
 /usr/lib/gcc/x86_64-linux-gnu/4.8/collect2 --sysroot=/ --build-id --eh-frame-hdr -m elf_x86_64 --hash-style=gnu --as-needed -dynamic-linker /lib64/ld-linux-x86-64.so.2 -z relro -o malc /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/crt1.o /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/crti.o /usr/lib/gcc/x86_64-linux-gnu/4.8/crtbegin.o -L/usr/lib/gcc/x86_64-linux-gnu/4.8 -L/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu -L/usr/lib/gcc/x86_64-linux-gnu/4.8/../../../../lib -L/lib/x86_64-linux-gnu -L/lib/../lib -L/usr/lib/x86_64-linux-gnu -L/usr/lib/../lib -L/usr/lib/gcc/x86_64-linux-gnu/4.8/../../.. /tmp/cc8sf3O6.o -rpath /software/code/c++workspace/glibc_bin_x64/lib -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib/gcc/x86_64-linux-gnu/4.8/crtend.o /usr/lib/gcc/x86_64-linux-gnu/4.8/../../../x86_64-linux-gnu/crtn.o

4)

   VirtualBox:/software/code/c++workspace/kernel$ ldd malc
    linux-vdso.so.1 =>  (0x00007ffeeabf2000)
    libc.so.6 => /software/code/c++workspace/glibc_bin_x64/lib/libc.so.6   (0x00007ff0ede98000)
    /lib64/ld-linux-x86-64.so.2 (0x0000560d287e1000)

  VirtualBox:/software/code/c++workspace/kernel$ ./malc
  Segmentation fault

I don't have much knowledge about linux c programming. Maybe the output give the clue.

My question is why the program is not working if link to glibc share lib which is compiled by myself?

Upate 1: add gdb output:

VirtualBox:/software/code/c++workspace/kernel$ gdb ./malc
GNU gdb (Ubuntu 7.7.1-0ubuntu5~14.04.2) 7.7.1
....
Type "apropos word" to search for commands related to "word"...
Reading symbols from ./malc...done.
gdb-peda$ run
Starting program: /software/code/c++workspace/kernel/malc 

Program received signal SIGSEGV, Segmentation fault.

[----------------------------------registers-----------------------------------]
RAX: 0x7ffff7ffccc0 --> 0x4040d00000000 
RBX: 0x7ffff7a40000 (jg     0x7ffff7a40047)
RCX: 0x7ffff7dee828 (<_dl_open+904>:    sub    %eax,%esp)
RDX: 0x7fffffffdad8 --> 0x7fffffffdae0 --> 0x2000000000 ('')
RSI: 0x7ffff7dee4a0 (<_dl_open>:    push   %rbp)
RDI: 0x7ffff7b9e892 (pop    %rdi)
RBP: 0x7fffffffdc70 --> 0x7fffffffdd80 --> 0x9 ('\t')
RSP: 0x7fffffffdab8 --> 0x7ffff7b5bd6d (mov    0x18(%rsp),%rdx)
RIP: 0x0 
R8 : 0x7fffffffdb10 --> 0x7ffff7b9cbe8 (rex.WR)
R9 : 0x0 
R10: 0x0 
R11: 0x0 
R12: 0x7ffff7a5fa88 (pushq  $0x3940)
R13: 0x7ffff7a5fb00 (sbb    %al,0x39(%rax))
R14: 0x394080 
R15: 0x7ffff7ff75b0 --> 0x7ffff7a40000 (jg     0x7ffff7a40047)
EFLAGS: 0x10246 (carry PARITY adjust ZERO sign trap INTERRUPT direction overflow)
[-------------------------------------code-------------------------------------]
Invalid $PC address: 0x0
[------------------------------------stack-------------------------------------]
0000| 0x7fffffffdab8 --> 0x7ffff7b5bd6d (mov    0x18(%rsp),%rdx)
0008| 0x7fffffffdac0 --> 0x7fff00000000 
0016| 0x7fffffffdac8 --> 0x0 
0024| 0x7fffffffdad0 --> 0x0 
0032| 0x7fffffffdad8 --> 0x7fffffffdae0 --> 0x2000000000 ('')
0040| 0x7fffffffdae0 --> 0x2000000000 ('')
0048| 0x7fffffffdae8 --> 0x0 
0056| 0x7fffffffdaf0 --> 0x0 
[------------------------------------------------------------------------------]
Legend: code, data, rodata, value
Stopped reason: SIGSEGV
0x0000000000000000 in ?? ()
gdb-peda$ bt
#0  0x0000000000000000 in ?? ()
#1  0x00007ffff7b5bd6d in ?? ()
#2  0x00007fff00000000 in ?? ()
#3  0x0000000000000000 in ?? ()
gdb-peda$

Update 2: As per the reply, I change my code to :

int main()
{
    char *str = NULL;
    //str = (char *)malloc(sizeof(char));
    //*str = 'a';

    str = malloc(sizeof(*str)*2);
    memset(str,0,sizeof(*str)*2);
    //strcpy(str,"a");
    str[0]='a';
    ////str[1]='\n';  //here is a mistake.
    str[1]='\0';      

    char *p = (char *)realloc(str, sizeof(char) * 10);
    if (p != NULL)
    {
        str = p;
    }

    printf("%s\n", str);

    return 0;
}

VirtualBox:/software/code/c++workspace/kernel$ gcc -g -O0 -v -da -Q -o malc malloc.c
VirtualBox:/software/code/c++workspace/kernel$ ./malc
a

VirtualBox:/software/code/c++workspace/kernel$ gcc -g -O0 -v -da -Q -o malc malloc.c -Wl,-rpath /software/code/c++workspace/glibc_bin_x64/lib
VirtualBox:/software/code/c++workspace/kernel$ ./malc
Segmentation fault

Update 3: I change my code, I install valgrind, and give the valgrind output.

I think my compiled libc.so is likely to have some different. I doesn't post the configure/make/make install of the glibc because I thought I had install the libc.so correctly(I didn't see any error listed during installing).

#include <stdio.h>
#include <stdlib.h>

int main()
{
    char *str = NULL;
    str = malloc(4);
    strcpy(str,"a"); 
    printf("%s\n", str);

    return 0;
}

VirtualBox:/software/code/c++workspace/kernel$ gcc -g -O0 -v -da -Q -o malc malloc.c -Wl,-rpath /software/code/c++workspace/glibc_bin_x64/lib

VirtualBox:/software/code/c++workspace/kernel$ valgrind -v --tool=memcheck --leak-check=full ./malc

==27238== Memcheck, a memory error detector
==27238== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==27238== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==27238== Command: ./malc
==27238== 
--27238-- Valgrind options:
--27238--    -v
--27238--    --tool=memcheck
--27238--    --leak-check=full
--27238-- Contents of /proc/version:
--27238--   Linux version 4.4.0-31-generic (buildd@lgw01-43) (gcc version 4.8.4 (Ubuntu 4.8.4-2ubuntu1~14.04.3) ) #50~14.04.1-Ubuntu SMP Wed Jul 13 01:07:32 UTC 2016
--27238-- Arch and hwcaps: AMD64, LittleEndian, amd64-cx16-rdtscp-sse3-avx
--27238-- Page sizes: currently 4096, max supported 4096
--27238-- Valgrind library directory: /usr/lib/valgrind
--27238-- Reading syms from /software/code/c++workspace/kernel/malc
--27238-- Reading syms from /lib/x86_64-linux-gnu/ld-2.19.so
--27238--   Considering /lib/x86_64-linux-gnu/ld-2.19.so ..
--27238--   .. CRC mismatch (computed 84cd48b7 wanted 021f91fa)
--27238--   Considering /usr/lib/debug/lib/x86_64-linux-gnu/ld-2.19.so ..
--27238--   .. CRC is valid
--27238-- Reading syms from /usr/lib/valgrind/memcheck-amd64-linux
--27238--   Considering /usr/lib/valgrind/memcheck-amd64-linux ..
--27238--   .. CRC mismatch (computed fed8e6c5 wanted e6be554a)
--27238--    object doesn't have a symbol table
--27238--    object doesn't have a dynamic symbol table
--27238-- Scheduler: using generic scheduler lock implementation.
--27238-- Reading suppressions file: /usr/lib/valgrind/default.supp
==27238== embedded gdbserver: reading from /tmp/vgdb-pipe-from-vgdb-to-27238-by-abbott-on-???
==27238== embedded gdbserver: writing to   /tmp/vgdb-pipe-to-vgdb-from-27238-by-abbott-on-???
==27238== embedded gdbserver: shared mem   /tmp/vgdb-pipe-shared-mem-vgdb-27238-by-abbott-on-???
==27238== 
==27238== TO CONTROL THIS PROCESS USING vgdb (which you probably
==27238== don't want to do, unless you know exactly what you're doing,
==27238== or are doing some strange experiment):
==27238==   /usr/lib/valgrind/../../bin/vgdb --pid=27238 ...command...
==27238== 
==27238== TO DEBUG THIS PROCESS USING GDB: start GDB like this
==27238==   /path/to/gdb ./malc
==27238== and then give GDB the following command
==27238==   target remote | /usr/lib/valgrind/../../bin/vgdb --pid=27238
==27238== --pid is optional if only one valgrind process is running
==27238== 
--27238-- REDIR: 0x4019e20 (ld-linux-x86-64.so.2:strlen) redirected to 0x380764b1 (???)
--27238-- Reading syms from /usr/lib/valgrind/vgpreload_core-amd64-linux.so
--27238--   Considering /usr/lib/valgrind/vgpreload_core-amd64-linux.so ..
--27238--   .. CRC mismatch (computed 4bcdfe99 wanted 3143e841)
--27238--    object doesn't have a symbol table
--27238-- Reading syms from /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so
--27238--   Considering /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so ..
--27238--   .. CRC mismatch (computed 3df18bf1 wanted 14fefe1c)
--27238--    object doesn't have a symbol table
==27238== WARNING: new redirection conflicts with existing -- ignoring it
--27238--     old: 0x04019e20 (strlen              ) R-> (0000.0) 0x380764b1 ???
--27238--     new: 0x04019e20 (strlen              ) R-> (2007.0) 0x04c2e1a0 strlen
--27238-- REDIR: 0x4019bd0 (ld-linux-x86-64.so.2:index) redirected to 0x4c2dd50 (index)
--27238-- REDIR: 0x4019df0 (ld-linux-x86-64.so.2:strcmp) redirected to 0x4c2f2f0 (strcmp)
--27238-- REDIR: 0x401ab40 (ld-linux-x86-64.so.2:mempcpy) redirected to 0x4c31da0 (mempcpy)
--27238-- Reading syms from /software/code/c++workspace/glibc_bin_x64/lib/libc-2.25.so
--27238-- REDIR: 0x4eba880 (libc.so.6:strcasecmp) redirected to 0x4a25720 (_vgnU_ifunc_wrapper)
==27238== Jump to the invalid address stated on the next line
==27238==    at 0x0: ???
==27238==    by 0x40043A1: dl_main (rtld.c:2237)
==27238==    by 0x40176F4: _dl_sysdep_start (dl-sysdep.c:249)
==27238==    by 0x4001BB7: _dl_start_final (rtld.c:347)
==27238==    by 0x4001BB7: _dl_start (rtld.c:573)
==27238==    by 0x4001267: ??? (in /lib/x86_64-linux-gnu/ld-2.19.so)
==27238==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
==27238== 
==27238== 
==27238== Process terminating with default action of signal 11 (SIGSEGV)
==27238==  Bad permissions for mapped region at address 0x0
==27238==    at 0x0: ???
==27238==    by 0x40043A1: dl_main (rtld.c:2237)
==27238==    by 0x40176F4: _dl_sysdep_start (dl-sysdep.c:249)
==27238==    by 0x4001BB7: _dl_start_final (rtld.c:347)
==27238==    by 0x4001BB7: _dl_start (rtld.c:573)
==27238==    by 0x4001267: ??? (in /lib/x86_64-linux-gnu/ld-2.19.so)
==27238== Jump to the invalid address stated on the next line
==27238==    at 0x5A6: ???
==27238==    by 0x4F52D6C: _dl_vdso_vsym (dl-vdso.c:40)
==27238==    by 0x4EDE814: time (in /software/code/c++workspace/glibc_bin_x64/lib/libc-2.25.so)
==27238==    by 0x400C4EA: elf_machine_lazy_rel (dl-machine.h:529)
==27238==    by 0x400C4EA: elf_dynamic_do_Rela (do-rel.h:77)
==27238==    by 0x400C4EA: _dl_relocate_object (dl-reloc.c:264)
==27238==    by 0x40043A1: dl_main (rtld.c:2237)
==27238==    by 0x40176F4: _dl_sysdep_start (dl-sysdep.c:249)
==27238==    by 0x4001BB7: _dl_start_final (rtld.c:347)
==27238==    by 0x4001BB7: _dl_start (rtld.c:573)
==27238==    by 0x4001267: ??? (in /lib/x86_64-linux-gnu/ld-2.19.so)
==27238==  Address 0x5a6 is not stack'd, malloc'd or (recently) free'd
==27238== 
==27238== 
==27238== Process terminating with default action of signal 11 (SIGSEGV)
==27238==  Bad permissions for mapped region at address 0x5A6
==27238==    at 0x5A6: ???
==27238==    by 0x4F52D6C: _dl_vdso_vsym (dl-vdso.c:40)
==27238==    by 0x4EDE814: time (in /software/code/c++workspace/glibc_bin_x64/lib/libc-2.25.so)
==27238==    by 0x400C4EA: elf_machine_lazy_rel (dl-machine.h:529)
==27238==    by 0x400C4EA: elf_dynamic_do_Rela (do-rel.h:77)
==27238==    by 0x400C4EA: _dl_relocate_object (dl-reloc.c:264)
==27238==    by 0x40043A1: dl_main (rtld.c:2237)
==27238==    by 0x40176F4: _dl_sysdep_start (dl-sysdep.c:249)
==27238==    by 0x4001BB7: _dl_start_final (rtld.c:347)
==27238==    by 0x4001BB7: _dl_start (rtld.c:573)
==27238==    by 0x4001267: ??? (in /lib/x86_64-linux-gnu/ld-2.19.so)
==27238== 
==27238== HEAP SUMMARY:
==27238==     in use at exit: 0 bytes in 0 blocks
==27238==   total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==27238== 
==27238== All heap blocks were freed -- no leaks are possible
==27238== 
==27238== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)
==27238== 
==27238== 1 errors in context 1 of 2:
==27238== Jump to the invalid address stated on the next line
==27238==    at 0x5A6: ???
==27238==    by 0x4F52D6C: _dl_vdso_vsym (dl-vdso.c:40)
==27238==    by 0x4EDE814: time (in /software/code/c++workspace/glibc_bin_x64/lib/libc-2.25.so)
==27238==    by 0x400C4EA: elf_machine_lazy_rel (dl-machine.h:529)
==27238==    by 0x400C4EA: elf_dynamic_do_Rela (do-rel.h:77)
==27238==    by 0x400C4EA: _dl_relocate_object (dl-reloc.c:264)
==27238==    by 0x40043A1: dl_main (rtld.c:2237)
==27238==    by 0x40176F4: _dl_sysdep_start (dl-sysdep.c:249)
==27238==    by 0x4001BB7: _dl_start_final (rtld.c:347)
==27238==    by 0x4001BB7: _dl_start (rtld.c:573)
==27238==    by 0x4001267: ??? (in /lib/x86_64-linux-gnu/ld-2.19.so)
==27238==  Address 0x5a6 is not stack'd, malloc'd or (recently) free'd
==27238== 
==27238== 
==27238== 1 errors in context 2 of 2:
==27238== Jump to the invalid address stated on the next line
==27238==    at 0x0: ???
==27238==    by 0x40043A1: dl_main (rtld.c:2237)
==27238==    by 0x40176F4: _dl_sysdep_start (dl-sysdep.c:249)
==27238==    by 0x4001BB7: _dl_start_final (rtld.c:347)
==27238==    by 0x4001BB7: _dl_start (rtld.c:573)
==27238==    by 0x4001267: ??? (in /lib/x86_64-linux-gnu/ld-2.19.so)
==27238==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
==27238== 
==27238== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 0 from 0)
Segmentation fault

Answer 1

It's got nothing to do with how you compile your code. Your code has a massive and obvious bug in it.

Strings in C have to be NUL terminated, otherwise when you try and do something with the string (ie print it out) you get undefined behaviour. Which is exactly what is happening here.

If you change

str = (char *)malloc(sizeof(char));
*str = 'a';

to be

str = malloc(sizeof(*str)*2);
strcpy(str,"a");

you will allocate enough space for the 2 characters you need (the "a" and the "\\0") and strcpy will add in the "\\0" character for you.

Alternatively you could do replace the strcpy and add the NUL character yourself like this

str[0]='a';
str[1]='\0';

or ensure your memory is entirely set to 0 with memset like this

memset(str,0,sizeof(*str)*2);