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.Dd October 31, 2024
.Dt RTLD_GET_VAR 3
.Os
.Sh NAME
.Nm rtld_get_var ,
.Nm rtld_set_var
.Nd query or change run-time linker parameters after image activation
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/errno.h
.In link.h
.Ft const char *
.Fn rtld_get_var "const char *name"
.Ft int
.Fn rtld_set_var "const char *name" "const char *value"
.Sh DESCRIPTION
The dynamic linker
.Xr rtld 1
can be configured by setting some environment variables for the process,
before image activation.
Sometimes it is desirable to query the current effective settings or
change them afterward.
.Pp
Since the process environment variables are maintained by higher-level
libraries, the run-time linker cannot access them after the image
activation.
The described functions make it possible to operate on rtld settings.
.Pp
The
.Fn rtld_get_var
function returns the current value of the named parameter.
.Pp
The
.Fn rtld_set_var
functions changes the value of the parameter to the new
.Fa value
value, if possible.
The
.Fa name
argument to both functions is the name of the parameter, which
is same as the corresponding environment variable
.Pq see Xr rtld 1
but without the
.Ev LD_
(or
.Ev LD_32_
or any other ABI-specific) prefix.
.Sh RETURN VALUES
The
.Fn rtld_get_var
returns the current value of the named parameter, or
.Dv NULL
if the name is invalid.
.Pp
The
.Fn rtld_set_var
returns 0 on success, or an integer indicating the error condition
which prevented the operation.
.Sh ERRORS
Possible errors returned from
.Fn rtld_set_var :
.Bl -tag -width Er
.It Bq Er EPERM
The requested change cannot be made at runtime, either because the
runtime linker can only take this parameter at initialization time,
or because the current process is executing with elevated privileges.
.It Bq ENOENT
The supplied parameter
.Fa name
is unknown.
.El
.Sh SEE ALSO
.Xr rtld 1
.Sh HISTORY
The
.Nm
function first appeared in
.Fx 15.0 .