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ld.so.8: Greatly expand the explanation of LD_DYNAMIC_WEAK 

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Michael Kerrisk 2017-05-08 16:12:31 +02:00
parent daad3ee975
commit 3337a4a3e0
1 changed files with 30 additions and 2 deletions
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@ -454,8 +454,23 @@ The default is standard error.
is ignored in secure-execution mode.
.TP
.BR LD_DYNAMIC_WEAK " (since glibc 2.1.91)"
If this environment variable is defined (with any value),
allow weak symbols to be overridden (reverting to old glibc behavior).
By default, when searching shared libraries to resolve a symbol reference,
the dynamic linker will resolve to the first definition it finds.
Old glibc versions (before 2.2), provided a different behavior:
if the linker found a symbol that was weak,
it would remember that symbol and
keep searching in the remaining shared libraries.
If it subsequently found a strong definition of the same symbol,
then it would instead use that definition.
(If no further symbol was found,
then the dynamic linker would use the weak symbol that it initially found.)
The old glibc behavior was nonstandard.
(Standard practice is that the distinction between between
weak and strong symbols should have effect only at static link time.)
In glibc 2.2
.\" More precisely 2.1.92
.\" See weak handling
.\" https://www.sourceware.org/ml/libc-hacker/2000-06/msg00029.html
.\" To: GNU libc hacker <libc-hacker at sourceware dot cygnus dot com>
@ -463,6 +478,19 @@ allow weak symbols to be overridden (reverting to old glibc behavior).
.\" From: Ulrich Drepper <drepper at redhat dot com>
.\" Date: 07 Jun 2000 20:08:12 -0700
.\" Reply-To: drepper at cygnus dot com (Ulrich Drepper)
the dynamic linker was modified to provide the current behavior
(which was the behavior that was provided by most other implementations
at that time).
Defining the
.B LD_DYNAMIC_WEAK
environment variable (with any value) provides
the old (nonstandard) glibc behavior,
whereby a weak symbol in one shared library may be overridden by
a strong symbol subsequently discovered in another shared library.
(Note that even when this variable is set,
a strong symbol in a shared library will not override
a weak definition of the same symbol in the main program.)
Since glibc 2.3.4,
.B LD_DYNAMIC_WEAK