[gcc r10-10794] libgcc, emutls: Allow building weak definitions of the emutls functions.

[gcc r10-10794] libgcc, emutls: Allow building weak definitions of the emutls functions.

[Iain D Sandoe]

https://gcc.gnu.org/g:dbdaf3fa2d7a9de8d7cc4682772240f3badb5ffe

commit r10-10794-gdbdaf3fa2d7a9de8d7cc4682772240f3badb5ffe
Author: Iain Sandoe <iain@sandoe.co.uk>
Date:   Sun Sep 19 12:35:46 2021 +0100

    libgcc, emutls: Allow building weak definitions of the emutls functions.
    
    In order to better support use of the emulated TLS between objects with
    DSO dependencies and static-linked libgcc, allow a target to make weak
    definitions.
    
    Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
    
    libgcc/ChangeLog:
    
            * config/t-darwin: Build weak-defined emutls objects.
            * emutls.c (__emutls_get_address): Add optional attributes.
            (__emutls_register_common): Likewise.
            (EMUTLS_ATTR): New.
    
    (cherry picked from commit b9873b4e2c9a9955789318f4d550147ef9405b07)

Diff:
---
 libgcc/config/t-darwin | 13 +++++++++++++
 libgcc/emutls.c        | 17 +++++++++++++++--
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/libgcc/config/t-darwin b/libgcc/config/t-darwin
index 4b6317b5d85..7e791b29f7a 100644
--- a/libgcc/config/t-darwin
+++ b/libgcc/config/t-darwin
@@ -15,6 +15,19 @@ crttme.o: $(srcdir)/config/darwin-crt-tm.c
 LIB2ADDEH = $(srcdir)/unwind-dw2.c $(srcdir)/config/unwind-dw2-fde-darwin.c \
   $(srcdir)/unwind-sjlj.c $(srcdir)/unwind-c.c
 
+# Make emutls weak so that we can deal with -static-libgcc, override the
+# hidden visibility when this is present in libgcc_eh.
+emutls.o: HOST_LIBGCC2_CFLAGS += \
+  -DEMUTLS_ATTR='__attribute__((__weak__,__visibility__("default")))'
+emutls_s.o: HOST_LIBGCC2_CFLAGS += \
+  -DEMUTLS_ATTR='__attribute__((__weak__,__visibility__("default")))'
+
+# Make the emutls crt as a convenience lib so that it can be linked
+# optionally, use the shared version so that we can link with DSO.
+libemutls_w.a: emutls_s.o
+	$(AR_CREATE_FOR_TARGET) $@ $<
+	$(RANLIB_FOR_TARGET) $@
+
 # Patch to __Unwind_Find_Enclosing_Function for Darwin10.
 d10-uwfef.o: $(srcdir)/config/darwin10-unwind-find-enc-func.c
 	$(crt_compile) -mmacosx-version-min=10.6 -c $<
diff --git a/libgcc/emutls.c b/libgcc/emutls.c
index f8012f6d8d5..a8ebe237d31 100644
--- a/libgcc/emutls.c
+++ b/libgcc/emutls.c
@@ -50,7 +50,16 @@ struct __emutls_array
   void **data[];
 };
 
+/* EMUTLS_ATTR is provided to allow targets to build the emulated tls
+   routines as weak definitions, for example.
+   If there is no definition, fall back to the default.  */
+#ifndef EMUTLS_ATTR
+#  define EMUTLS_ATTR
+#endif
+
+EMUTLS_ATTR
 void *__emutls_get_address (struct __emutls_object *);
+EMUTLS_ATTR
 void __emutls_register_common (struct __emutls_object *, word, word, void *);
 
 #ifdef __GTHREADS
@@ -123,7 +132,11 @@ emutls_alloc (struct __emutls_object *obj)
   return ret;
 }
 
-void *
+/* Despite applying the attribute to the declaration, in this case the mis-
+   match between the builtin's declaration [void * (*)(void *)] and the
+   implementation here, causes the decl. attributes to be discarded.  */
+
+EMUTLS_ATTR void *
 __emutls_get_address (struct __emutls_object *obj)
 {
   if (! __gthread_active_p ())
@@ -187,7 +200,7 @@ __emutls_get_address (struct __emutls_object *obj)
 #endif
 }
 
-void
+EMUTLS_ATTR void
 __emutls_register_common (struct __emutls_object *obj,
 			  word size, word align, void *templ)
 {