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* [glibc] manual, NEWS: Document malloc side effect of dynamic TLS changes
@ 2024-01-24  8:34 Florian Weimer
  0 siblings, 0 replies; only message in thread
From: Florian Weimer @ 2024-01-24  8:34 UTC (permalink / raw)
  To: glibc-cvs;h=486452affbac684db739b7fcca1e84e8a7ce33d1

commit 486452affbac684db739b7fcca1e84e8a7ce33d1
Author: Florian Weimer <>
Date:   Wed Jan 24 09:34:15 2024 +0100

    manual, NEWS: Document malloc side effect of dynamic TLS changes
    The increased malloc subsystem usage is a side effect of
    commit d2123d68275acc0f061e73d5f86ca504e0d5a344 ("elf: Fix slow tls
    access after dlopen [BZ #19924]").
    Reviewed-by: Szabolcs Nagy <>

 NEWS               | 6 ++++++
 manual/memory.texi | 8 ++++++++
 2 files changed, 14 insertions(+)

diff --git a/NEWS b/NEWS
index 4a11e9df0f..199f079f27 100644
--- a/NEWS
+++ b/NEWS
@@ -91,6 +91,12 @@ Deprecated and removed features, and other changes affecting compatibility:
   of GNU libc are advised to check whether their build processes can be
+* The dynamic linker calls the malloc and free functions in more cases
+  during TLS access if a shared object with dynamic TLS is loaded and
+  unloaded.  This can result in an infinite recursion if a malloc
+  replacement library or its dependencies use dynamic TLS instead of
+  initial-exec TLS.
 * The ia64*-*-linux-gnu configurations are no longer supported.
 Changes to build and runtime requirements:
diff --git a/manual/memory.texi b/manual/memory.texi
index 258fdbd3a0..fb875f4c3c 100644
--- a/manual/memory.texi
+++ b/manual/memory.texi
@@ -1815,6 +1815,14 @@ using shared object dependencies or @code{LD_PRELOAD}.  For static
 linking, the @code{malloc} replacement library must be linked in before
 linking against @code{libc.a} (explicitly or implicitly).
+Care must be taken not to use functionality from @theglibc{} that uses
+@code{malloc} internally.  For example, the @code{fopen},
+@code{opendir}, @code{dlopen}, and @code{pthread_setspecific} functions
+currently use the @code{malloc} subsystem internally.  If the
+replacement @code{malloc} or its dependencies use thread-local storage
+(TLS), it must use the initial-exec TLS model, and not one of the
+dynamic TLS variants.
 @strong{Note:} Failure to provide a complete set of replacement
 functions (that is, all the functions used by the application,
 @theglibc{}, and other linked-in libraries) can lead to static linking

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