ld: Prevent `_tls_used` and `_load_config_used` from being garbage-collected

LIU Hao <[email protected]> Mon, 27 Jul 2026 23:38:42 +0800

Newsgroups	gmane.comp.gnu.binutils
Message-ID	<[email protected]>

Hello,

Below is a patch that is required for LD to work with `--gc-sections` with recent mingw-w64, tested on 
x86_64-w64-mingw32 and i686-w64-mingw32.

I don't have access to binutils Git so please commit it for me. Also please consider backporting.



 From 9a98b90d43739f5979a999acda3beb21b17442b2 Mon Sep 17 00:00:00 2001
From: LIU Hao <[email protected]>
Date: Mon, 27 Jul 2026 23:11:54 +0800
Subject: [PATCH] ld: Prevent `_tls_used` and `_load_config_used` from being
  garbage-collected

Earlier today I pushed some patches to mingw-w64 to make `_tls_used` only
linked on demand, by referencing it indirectly through tentative definitions.
However, since the startup code no longer has strong references to `_tls_used`,
if LD is passed `--gc-sections`, it garbage-collects `_tls_used`, resulting in
a broken executable:

    $ objdump -p bin/test_thread_id_cpp.exe | grep -F .tls
    Entry 9 ffffffffc0000000 00000028 Thread Storage Directory [.tls]

This patch prevents `_tls_used` from being garbage-collected, and likewise for
`_load_config_used`.

Signed-off-by: LIU Hao <[email protected]>
---
  ld/emultempl/pe.em  | 10 ++++++++++
  ld/emultempl/pep.em |  5 +++++
  2 files changed, 15 insertions(+)

diff --git a/ld/emultempl/pe.em b/ld/emultempl/pe.em
index 07ef2ca5953..475e0349ff8 100644
--- a/ld/emultempl/pe.em
+++ b/ld/emultempl/pe.em
@@ -1573,6 +1573,16 @@ gld${EMULATION_NAME}_after_open (void)

    pe_output_file_set_long_section_names (link_info.output_bfd);

+  /* The RVAs of these symbols will be written into the PE header, so they
+     must not be collected.  */
+#if defined (TARGET_IS_i386pe)
+  lang_add_gc_name ("__tls_used");
+  lang_add_gc_name ("__load_config_used");
+#else
+  lang_add_gc_name ("_tls_used");
+  lang_add_gc_name ("_load_config_used");
+#endif
+
  #ifdef DLL_SUPPORT
    pe_process_import_defs (link_info.output_bfd, &link_info);

diff --git a/ld/emultempl/pep.em b/ld/emultempl/pep.em
index 14be8435685..1ab5c4d88f7 100644
--- a/ld/emultempl/pep.em
+++ b/ld/emultempl/pep.em
@@ -1624,6 +1624,11 @@ gld${EMULATION_NAME}_after_open (void)

    pep_output_file_set_long_section_names (link_info.output_bfd);

+  /* The RVAs of these symbols will be written into the PE header, so they
+     must not be collected.  */
+  lang_add_gc_name ("_tls_used");
+  lang_add_gc_name ("_load_config_used");
+
  #ifdef DLL_SUPPORT
    pep_process_import_defs (link_info.output_bfd, &link_info);

-- 
2.55.0

2004-ld-Prevent-_tls_used-and-_load_config_used-from-bein.patch (text/plain, 2.1 KB)

From 9a98b90d43739f5979a999acda3beb21b17442b2 Mon Sep 17 00:00:00 2001
From: LIU Hao <[email protected]>
Date: Mon, 27 Jul 2026 23:11:54 +0800
Subject: [PATCH] ld: Prevent `_tls_used` and `_load_config_used` from being
 garbage-collected

Earlier today I pushed some patches to mingw-w64 to make `_tls_used` only
linked on demand, by referencing it indirectly through tentative definitions.
However, since the startup code no longer has strong references to `_tls_used`,
if LD is passed `--gc-sections`, it garbage-collects `_tls_used`, resulting in
a broken executable:

   $ objdump -p bin/test_thread_id_cpp.exe | grep -F .tls
   Entry 9 ffffffffc0000000 00000028 Thread Storage Directory [.tls]

This patch prevents `_tls_used` from being garbage-collected, and likewise for
`_load_config_used`.

Signed-off-by: LIU Hao <[email protected]>
---
 ld/emultempl/pe.em  | 10 ++++++++++
 ld/emultempl/pep.em |  5 +++++
 2 files changed, 15 insertions(+)

diff --git a/ld/emultempl/pe.em b/ld/emultempl/pe.em
index 07ef2ca5953..475e0349ff8 100644
--- a/ld/emultempl/pe.em
+++ b/ld/emultempl/pe.em
@@ -1573,6 +1573,16 @@ gld${EMULATION_NAME}_after_open (void)
 
   pe_output_file_set_long_section_names (link_info.output_bfd);
 
+  /* The RVAs of these symbols will be written into the PE header, so they
+     must not be collected.  */
+#if defined (TARGET_IS_i386pe)
+  lang_add_gc_name ("__tls_used");
+  lang_add_gc_name ("__load_config_used");
+#else
+  lang_add_gc_name ("_tls_used");
+  lang_add_gc_name ("_load_config_used");
+#endif
+
 #ifdef DLL_SUPPORT
   pe_process_import_defs (link_info.output_bfd, &link_info);
 
diff --git a/ld/emultempl/pep.em b/ld/emultempl/pep.em
index 14be8435685..1ab5c4d88f7 100644
--- a/ld/emultempl/pep.em
+++ b/ld/emultempl/pep.em
@@ -1624,6 +1624,11 @@ gld${EMULATION_NAME}_after_open (void)
 
   pep_output_file_set_long_section_names (link_info.output_bfd);
 
+  /* The RVAs of these symbols will be written into the PE header, so they
+     must not be collected.  */
+  lang_add_gc_name ("_tls_used");
+  lang_add_gc_name ("_load_config_used");
+
 #ifdef DLL_SUPPORT
   pep_process_import_defs (link_info.output_bfd, &link_info);
 
-- 
2.55.0

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