[PATCH] libio: Properly link in libio functions in static binaries

[H.J. Lu]

commit 3020f72618e4f1d7338cd42b8bc7b2813e961b5a
Author: Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>
Date:   Tue Dec 27 18:11:43 2022 -0300

    libio: Remove the usage of __libc_IO_vtables

added

 #define libio_static_fn_required(name) __asm (".globl " #name);

to link in libio functions in static binaries.  But there is no relocation
in
	.globl	_IO_file_open

and "strip --strip-unneeded" will remove such unreferenced symbols which
breaks static binaries.  Redefine libio_static_fn_required to create a
reference to the required function with

	.pushsection ".data.rel.ro.local","aw"
.L_IO_file_open:
	.dc.a	_IO_file_open
	.popsection

This fixes BZ #33300.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
---
 libio/Makefile           |  9 +++++++++
 libio/libioP.h           |  6 +++++-
 libio/tst-stdio-static.c | 28 ++++++++++++++++++++++++++++
 3 files changed, 42 insertions(+), 1 deletion(-)
 create mode 100644 libio/tst-stdio-static.c

diff --git a/libio/Makefile b/libio/Makefile
index f020f8ec4d..6ce669e103 100644
--- a/libio/Makefile
+++ b/libio/Makefile
@@ -130,6 +130,7 @@ tests = \
   tst-sprintf-chk-ub \
   tst-sprintf-ub \
   tst-sscanf \
+  tst-stdio-static \
   tst-swscanf \
   tst-ungetwc1 \
   tst-ungetwc2 \
@@ -149,6 +150,8 @@ tests = \
   tst_wscanf \
   # tests
 
+tests-static += tst-stdio-static
+
 $(objpfx)tst-popen-fork: $(shared-thread-library)
 
 tests-internal = tst-vtables tst-vtables-interposed
@@ -445,3 +448,9 @@ $(objpfx)tst-bz22415-mem.out: $(objpfx)tst-bz22415.out
 $(objpfx)tst-bz24228-mem.out: $(objpfx)tst-bz24228.out
 	$(common-objpfx)malloc/mtrace $(objpfx)tst-bz24228.mtrace > $@; \
 	$(evaluate-test)
+
+# Test stdio.o with "strip --strip-unneeded".
+$(objpfx)tst-stdio-static: $(objpfx)stdio-stripped.o
+
+$(objpfx)stdio-stripped.o: $(objpfx)stdio.o
+	$(STRIP) --strip-unneeded -o $@ $<
diff --git a/libio/libioP.h b/libio/libioP.h
index 1e3d28bb34..24958676b1 100644
--- a/libio/libioP.h
+++ b/libio/libioP.h
@@ -535,7 +535,11 @@ extern const struct _IO_jump_t __io_vtables[] attribute_hidden;
 #ifdef SHARED
 # define libio_static_fn_required(name)
 #else
-# define libio_static_fn_required(name) __asm (".globl " #name);
+# define libio_static_fn_required(name) \
+  __asm (".pushsection \".data.rel.ro.local\",\"aw\"\n" \
+".L"#name":\n" \
+"	.dc.a	" #name"\n" \
+"	.popsection");
 #endif
 
 extern int _IO_do_write (FILE *, const char *, size_t);
diff --git a/libio/tst-stdio-static.c b/libio/tst-stdio-static.c
new file mode 100644
index 0000000000..48c7f76e6e
--- /dev/null
+++ b/libio/tst-stdio-static.c
@@ -0,0 +1,28 @@
+/* Test static stdio.o with "strip --strip-unneeded".
+   Copyright (C) 2025 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <stdio.h>
+
+/* NB: Call main directly to trigger BZ #33300.  */
+
+int
+main (void)
+{
+  printf ("OK\n");
+  return 0;
+}
-- 
2.50.1