'\" t .\" Copyright (C) 2015 Michael Kerrisk .\" .\" %%%LICENSE_START(VERBATIM) .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" %%%LICENSE_END .\" .TH DLINFO 3 2015-08-08 "Linux" "Linux Programmer's Manual" .SH NAME dlinfo \- obtain information about a dynamically loaded object .SH SYNOPSIS .nf .B #define _GNU_SOURCE .B #include .B #include .BR "int dlinfo(void *" handle ", int " request ", void *" info ); Link with \fI\-ldl\fP. .fi .SH DESCRIPTION The .BR dlinfo () function obtains information about the dynamically loaded object referred to by .IR handle (typically obtained by an earlier call to .BR dlopen (3) or .BR dlmopen (3)). The .I request argument specifies which information is to be returned. The .I info argument is a pointer to a buffer used to store information returned by the call; the type of this argument depends on .IR request . The following values are supported for .IR request (with the corresponding type for .IR info shown in parentheses): .TP .BR RTLD_DI_LMID " (\fILmid_t *\fP)" Obtain the ID of the link-map list (namespace) in which .I handle is loaded. .TP .BR RTLD_DI_LINKMAP " (\fIstruct link_map **\fP)" Obtain a pointer to the .I link_map structure corresponding to .IR handle . The .IR info argument points to a pointer to a .I link_map structure, defined in .I as: .in +4n .nf struct link_map { ElfW(Addr) l_addr; /* Difference between the address in the ELF file and the address in memory */ char *l_name; /* Absolute pathname where object was found */ ElfW(Dyn) *l_ld; /* Dynamic section of the shared object */ struct link_map *l_next, *l_prev; /* Chain of loaded objects */ /* Plus additional fields private to the implementation */ }; .fi .in .TP .BR RTLD_DI_ORIGIN " (\fIchar *\fP)" Copy the pathname of the origin of the shared object corresponding to .IR handle to the location pointed to by .IR info . .TP .BR RTLD_DI_SERINFO " (\fIDl_serinfo *\fP)" Obtain the library search paths for the shared object referred to by .IR handle . The .I info argument is a pointer to a .I Dl_serinfo that contains the search paths. Because the number of search paths may vary, the size of the structure pointed to by .IR info can vary. The .B RTLD_DI_SERINFOSIZE request described below allows applications to size the buffer suitably. The caller must perform the following steps: .RS .IP 1. 3 Use a .B RTLD_DI_SERINFOSIZE request to populate a .I Dl_serinfo structure with the size .RI ( dls_size ) of the structure needed for the subsequent .B RTLD_DI_SERINFO request. .IP 2. Allocate a .I Dl_serinfo buffer of the correct size .RI ( dls_size ). .IP 3. Use a further .B RTLD_DI_SERINFOSIZE request to populate the .I dls_size and .I dls_cnt fields of the buffer allocated in the previous step. .IP 4. Use a .B RTLD_DI_SERINFO to obtain the library search paths. .IP .RE .IP The .I Dl_serinfo structure is defined as follows: .in +4n .nf typedef struct { size_t dls_size; /* Size in bytes of the whole buffer */ unsigned int dls_cnt; /* Number of elements in 'dls_serpath' */ Dl_serpath dls_serpath[1]; /* Actually longer, 'dls_cnt' elements */ } Dl_serinfo; .fi .in Each of the .I dls_serpath elements in the above structure is a structure of the following form: .in +4n .nf typedef struct { char *dls_name; /* Name of library search path directory */ unsigned int dls_flags; /* Indicates where this directory came from */ } Dl_serpath; .fi .in The .I dls_flags field is currently unused, and always contains zero. .TP .BR RTLD_DI_SERINFOSIZE " (\fIDl_serinfo *\fP)" Populate the .I dls_size and .I dls_cnt fields of the .I Dl_serinfo structure pointed to by .IR info with values suitable for allocating a buffer for use in a subsequent .B RTLD_DI_SERINFO request. .TP .BR RTLD_DI_TLS_MODID " (\fIsize_t *\fP, since glibc 2.4)" Obtain the module ID of this shared object's TLS (thread-local storage) segment, as used in TLS relocations. If this object does not define a TLS segment, zero is placed in .IR *info . .TP .BR RTLD_DI_TLS_DATA " (\fIvoid **\fP, since glibc 2.4)" Obtain a pointer to the calling thread's TLS block corresponding to this shared object's TLS segment. If this object does not define a PT_TLS segment, or if the calling thread has not allocated a block for it, NULL is placed in .IR *info . .SH RETURN VALUE On success, .BR dlinfo () returns 0. On failure, it returns \-1; the cause of the error can be diagnosed using .BR dlerror (3). .SH VERSIONS .BR dlinfo () first appeared in glibc 2.3.3. .SH ATTRIBUTES For an explanation of the terms used in this section, see .BR attributes (7). .TS allbox; lb lb lb l l l. Interface Attribute Value T{ .BR dlinfo () T} Thread safety MT-Safe .TE .SH CONFORMING TO This function is a nonstandard GNU extension. .SH NOTES This function derives from the Solaris function of the same name and also appears on some other systems. The sets of requests supported by the various implementations overlaps only partially. .SH EXAMPLE The program below opens a shared objects using .BR dlopen (3) and then uses the .B RTLD_DI_SERINFOSIZE and .B RTLD_DI_SERINFO requests to obtain the library search path list for the library. Here is an example of what we might see when running the program: .in +4n .nf $ \fB./a.out /lib64/libm.so.6\fP dls_serpath[0].dls_name = /lib64 dls_serpath[1].dls_name = /usr/lib64 .fi .in .SS Program source \& .nf #define _GNU_SOURCE #include #include #include #include int main(int argc, char *argv[]) { void *handle; Dl_serinfo serinfo; Dl_serinfo *sip; int j; if (argc != 2) { fprintf(stderr, "Usage: %s \\n", argv[0]); exit(EXIT_FAILURE); } /* Obtain a handle for shared objects specified on command line */ handle = dlopen(argv[1], RTLD_NOW); if (handle == NULL) { fprintf(stderr, "dlopen() failed: %s\\n", dlerror()); exit(EXIT_FAILURE); } /* Discover the size of the buffer that we must pass to RTLD_DI_SERINFO */ if (dlinfo(handle, RTLD_DI_SERINFOSIZE, &serinfo) == \-1) { fprintf(stderr, "RTLD_DI_SERINFOSIZE failed: %s\\n", dlerror()); exit(EXIT_FAILURE); } /* Allocate the buffer for use with RTLD_DI_SERINFO */ sip = malloc(serinfo.dls_size); if (sip == NULL) { perror("malloc"); exit(EXIT_FAILURE); } /* Initialize the \(aqdls_size\(aq and \(aqdls_cnt\(aq fields in the newly allocated buffer */ if (dlinfo(handle, RTLD_DI_SERINFOSIZE, sip) == \-1) { fprintf(stderr, "RTLD_DI_SERINFOSIZE failed: %s\\n", dlerror()); exit(EXIT_FAILURE); } /* Fetch and print library search list */ if (dlinfo(handle, RTLD_DI_SERINFO, sip) == \-1) { fprintf(stderr, "RTLD_DI_SERINFO failed: %s\\n", dlerror()); exit(EXIT_FAILURE); } for (j = 0; j < serinfo.dls_cnt; j++) printf("dls_serpath[%d].dls_name = %s\\n", j, sip\->dls_serpath[j].dls_name); exit(EXIT_SUCCESS); } .fi .SH SEE ALSO .BR dl_iterate_phdr (3), .BR dladdr (3), .BR dlerror (3), .BR dlopen (3), .BR dlsym (3), .BR ld.so (8) .SH COLOPHON This page is part of release 4.10 of the Linux .I man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/.