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Date:      Sat, 08 May 2021 07:10:55 +0000
From:      bugzilla-noreply@freebsd.org
To:        bugs@FreeBSD.org
Subject:   [Bug 255698] dlerror() returns non-NULL after a successful call to dlopen()/dlsym()
Message-ID:  <bug-255698-227@https.bugs.freebsd.org/bugzilla/>
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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=255698

            Bug ID: 255698
           Summary: dlerror() returns non-NULL after a successful call to
                    dlopen()/dlsym()
           Product: Base System
           Version: CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: bin
          Assignee: bugs@FreeBSD.org
          Reporter: astralblue@gmail.com

dlerror() used to return NULL after a successful call to other dl family of
functions, such as dlopen() and dlsym().  Starting recently, dlerror() started
returning non-NULL message after such successful calls.  The message is
initially an empty string, or an error message most recently seen—even if the
most recent dlXXXX() call was successful.

Test program:

#include <dlfcn.h>
#include <stdio.h>

#define PRINT_DLERROR() do { \
        char const *err = dlerror(); \
        printf("dlerror()=%p", err); \
        if (err) printf(" (%s)", err); \
        printf("\n"); \
} while (0)

void
test_dlopen(char const *path)
{
        void *handle = dlopen(path, RTLD_NOW);
        printf("dlopen(%s, RTLD_NOW)=%p\n", path, handle);
        PRINT_DLERROR();
        PRINT_DLERROR();
        if (handle)
                dlclose(handle);
}

int
main()
{
        PRINT_DLERROR();
        PRINT_DLERROR();
        test_dlopen("/foobar.so");
        test_dlopen("/usr/lib/libm.so");
        return 0;
}

Expected result (taken on a 12.2-RELEASE-p2 jail, note dlerror() returns NULL
upon a successful dlopen()):

dlerror()=0x0
dlerror()=0x0
dlopen(/foobar.so, RTLD_NOW)=0x0
dlerror()=0x8002296c0 (Cannot open "/foobar.so")
dlerror()=0x0
dlopen(/usr/lib/libm.so, RTLD_NOW)=0x80022e800
dlerror()=0x0
dlerror()=0x0

Actual result (taken on a -CURRENT system, built from main branch commit
34abb05be77a32a2b2673fb4b85eaa53a3d1446e, note dlerror() returns non-NULL on
the first dlerror() call, even after a successful dlopen() and also before the
first dlopen(), also note the dlerror() message after a successful dlopen() is
from the previous failure):

34abb05be77a32a2b2673fb4b85eaa53a3d1446e

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