Tag: Linux

Fix “cannot find libasan_preinit.o” issue in Void Linux

In my Void Linux, using clang with -fsanitize=address option is OK:

$ clang -std=c11 -fsanitize=address test.c
$

Whilst gcc reports following error:

$ gcc -std=c11 -fsanitize=address test.c
/usr/bin/ld: cannot find libasan_preinit.o: No such file or directory
/usr/bin/ld: cannot find -lasan
collect2: error: ld returned 1 exit status

The solution is to install libsanitizer-devel:

$ sudo xbps-install -Su libsanitizer-devel
$ gcc -std=c11 -fsanitize=address test.c
$

Check the linked libraries of executalbe file:

$ ldd a.out
    linux-vdso.so.1 (0x00007fff1a58b000)
    libasan.so.5 => /usr/lib/libasan.so.5 (0x00007fc1f0f02000)
    libc.so.6 => /usr/lib/libc.so.6 (0x00007fc1f0d3f000)
    libdl.so.2 => /usr/lib/../lib/libdl.so.2 (0x00007fc1f0d3a000)
    librt.so.1 => /usr/lib/../lib/librt.so.1 (0x00007fc1f0d2f000)
    libpthread.so.0 => /usr/lib/../lib/libpthread.so.0 (0x00007fc1f0d0e000)
    libstdc++.so.6 => /usr/lib/../lib/libstdc++.so.6 (0x00007fc1f0a99000)
    libm.so.6 => /usr/lib/../lib/libm.so.6 (0x00007fc1f0952000)
    libgcc_s.so.1 => /usr/lib/../lib/libgcc_s.so.1 (0x00007fc1f0938000)
    /lib/ld-linux-x86-64.so.2 (0x00007fc1f193d000)

Reference:
How to use gcc with sanitizers in Void Linux?.

The alignment of dynamically allocating memory

Check Notes from max_align_t:

Pointers returned by allocation functions such as malloc are suitably aligned for any object, which means they are aligned at least as strictly as max_align_t.

It means the memory allocated dynamically is guaranteed to alignof(max_align_t) bytes aligned.

Check Notes from aligned_alloc:

Passing a size which is not an integral multiple of alignment or a alignment which is not valid or not supported by the implementation causes the function to fail and return a null pointer (C11, as published, specified undefined behavior in this case, this was corrected by DR 460).

It means the alignment for aligned_alloc is implementation dependent.

Write a simple program to test aligned_alloc behavior in macOS and Linux (X86_64):

$ cat align.c
#include <stdalign.h>
#include <stddef.h>
#include <stdio.h>
#include <stdlib.h>

int main()
{
    printf("alignof(max_align_t)=%zu\n\n", alignof(max_align_t));

    size_t size = 1024;
    size_t align[] = {1, 2, 4, 8, 16, 32, 64};
    for (size_t i = 0; i < sizeof(align) / sizeof(align[0]); i++)
    {
        void *p = aligned_alloc(align[i], size);
        printf("align=%zu, pointer is %p\n", align[i], p);
        free(p);
    }
}

Build and run it in macOS:

$ cc align.c -o align
$ ./align
alignof(max_align_t)=16

align=1, pointer is 0x0
align=2, pointer is 0x0
align=4, pointer is 0x0
align=8, pointer is 0x7fbd48801600
align=16, pointer is 0x7fbd48801600
align=32, pointer is 0x7fbd48801600
align=64, pointer is 0x7fbd48801600

In Linux (X86_64):

$ cc align.c -o align
$ ./align
alignof(max_align_t)=16

align=1, pointer is 0x5645aec676b0
align=2, pointer is 0x5645aec676b0
align=4, pointer is 0x5645aec676b0
align=8, pointer is 0x5645aec676b0
align=16, pointer is 0x5645aec676b0
align=32, pointer is 0x5645aec67ac0
align=64, pointer is 0x5645aec67f40

Both macOS and Linux (X86_64) have the same alignment of allocating memory from free storage: 16 bytes. macOS requires the alignment of aligned_alloc is at least 8 bytes; whilst Linux (X86_64) doesn’t have this requirement.

P.S., the code can be downloaded here.

Be aware of huge pages in Linux

On a freshly installed Linux machine, I find my application will crash unexpectly:

==5611==AddressSanitizer's allocator is terminating the process instead of returning 0
==5611==If you don't like this behavior set allocator_may_return_null=1
==5611==AddressSanitizer CHECK failed: ../../../../libsanitizer/sanitizer_common/sanitizer_allocator.cc:216 "((0)) != (0)" (0x0, 0x0)
    #0 0x7f7dc13b94a2  (/lib64/libasan.so.5+0xf94a2)
    #1 0x7f7dc13d60a9 in __sanitizer::CheckFailed(char const*, int, char const*, unsigned long long, unsigned long long) (/lib64/libasan
.so.5+0x1160a9)
    #2 0x7f7dc13bf3d6  (/lib64/libasan.so.5+0xff3d6)
    #3 0x7f7dc13bf43a  (/lib64/libasan.so.5+0xff43a)
    #4 0x7f7dc12e9319  (/lib64/libasan.so.5+0x29319)
    #5 0x7f7dc12e6f56  (/lib64/libasan.so.5+0x26f56)
    #6 0x7f7dc13adeba in malloc (/lib64/libasan.so.5+0xedeba)
......

After debugging, the root cause is memory not enough. This is the memory usage in idle state:

The reason for memory usage is so high even in idle state is related to huge pages configuration:

$ cat /etc/default/grub
......
GRUB_CMDLINE_LINUX="rd.lvm.lv=centos/root rhgb quiet default_hugepagesz=1G hugepagesz=1G hugepages=100"

After shrinking huge pages usage, the application runs smoothly. About huge pages, this post is a good reference.

Enable Pressure Stall Information (PSI) on Void Linux

There are two configurations for Pressure Stall Information (PSI) feature in kernel: CONFIG_PSI for supporting PSI or not and CONFIG_PSI_DEFAULT_DISABLED for diabling PSI or not. Check my Void Linux configurations:

$ zgrep PSI /proc/config.gz
CONFIG_PSI=y
CONFIG_PSI_DEFAULT_DISABLED=y

We can see PSI is disabled by default, and it will incur following errors:

$ cat /proc/pressure/cpu
cat: /proc/pressure/cpu: Operation not supported

To enable this feature, add “psi=1” for GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub file:

$ cat /etc/default/grub
#
# Configuration file for GRUB.
#
......
GRUB_CMDLINE_LINUX_DEFAULT="loglevel=4 slub_debug=P page_poison=1 psi=1"

Then regenerating the grub configuration and reboot:

$ sudo grub-mkconfig -o /boot/grub/grub.cfg
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-5.2.13_1
Found initrd image: /boot/initramfs-5.2.13_1.img
done
$sudo reboot

The PSI is enabled:

$ cat /proc/pressure/cpu
some avg10=0.00 avg60=0.00 avg300=0.00 total=890919

References:
Getting Started with PSI;
Where are the current kernel build options stored?;
grub.