RISC-V problem with weak function references and -mcmodel=medany

[Sebastian Huber]

Hello,

I try to build a 64-bit RISC-V tool chain for RTEMS. RTEMS doesn't use 
virtual memory. The reference chips for 64-bit RISC-V such as FU540-C000 
locate the RAM at 0x8000_0000. This forces me to use -mcmodel=medany in 
64-bit mode. The ctrbegin.o contains this code (via crtstuff.c):

extern void *__deregister_frame_info (const void *)
          __attribute__ ((weak));
...
# 370 "libgcc/crtstuff.c"
static void __attribute__((used))
__do_global_dtors_aux (void)
{
   static _Bool completed;

   if (__builtin_expect (completed, 0))
     return;
# 413 "libgcc/crtstuff.c"
   deregister_tm_clones ();
# 423 "libgcc/crtstuff.c"
   if (__deregister_frame_info)
     __deregister_frame_info (__EH_FRAME_BEGIN__);



   completed = 1;
}

Which is:

     .text
     .align    1
     .type    __do_global_dtors_aux, @function
__do_global_dtors_aux:
     lbu    a5,completed.3298
     bnez    a5,.L22
     addi    sp,sp,-16
     sd    ra,8(sp)
     call    deregister_tm_clones
     lla    a5,__deregister_frame_info
     beqz    a5,.L17
     lla    a0,__EH_FRAME_BEGIN__
     call    __deregister_frame_info
.L17:
     ld    ra,8(sp)
     li    a5,1
     sb    a5,completed.3298,a4
     addi    sp,sp,16
     jr    ra
.L22:
     ret

If I link an executable I get this:

/opt/rtems/5/lib64/gcc/riscv64-rtems5/9.0.0/../../../../riscv64-rtems5/bin/ld: 
/opt/rtems/5/lib64/gcc/riscv64-rtems5/9.0.0/crtbegin.o: in function `.L0 ':
crtstuff.c:(.text+0x72): relocation truncated to fit: R_RISCV_CALL 
against undefined symbol `__deregister_frame_info'

I guess, that the resolution of the weak reference to the undefined 
symbol __deregister_frame_info somehow sets __deregister_frame_info to 
the absolute address 0 which is illegal in the following "call 
__deregister_frame_info"? Is this construct with weak references and a 
-mcmodel=medany supported on RISC-V at all?

If I change crtstuff.c like this using weak function definitions

diff --git a/libgcc/crtstuff.c b/libgcc/crtstuff.c
index 5e894455e16..770e3420c92 100644
--- a/libgcc/crtstuff.c
+++ b/libgcc/crtstuff.c
@@ -177,13 +177,24 @@ call_ ## FUNC 
(void)                                      \

  /* References to __register_frame_info and __deregister_frame_info should
     be weak in this file if at all possible.  */
-extern void __register_frame_info (const void *, struct object *)
-                                 TARGET_ATTRIBUTE_WEAK;
+extern void __register_frame_info (const void *, struct object *) ;
+TARGET_ATTRIBUTE_WEAK void __register_frame_info (const void *unused, 
struct object *unused2)
+{
+       (void)unused;
+       (void)unused2;
+}
+
  extern void __register_frame_info_bases (const void *, struct object *,
                                          void *, void *)
                                   TARGET_ATTRIBUTE_WEAK;
-extern void *__deregister_frame_info (const void *)
- TARGET_ATTRIBUTE_WEAK;
+
+extern void *__deregister_frame_info (const void *);
+TARGET_ATTRIBUTE_WEAK void *__deregister_frame_info (const void *unused)
+{
+       (void)unused;
+       return 0;
+}
+
  extern void *__deregister_frame_info_bases (const void *)
TARGET_ATTRIBUTE_WEAK;
  extern void __do_global_ctors_1 (void);

then the example program links.

-- 
Sebastian Huber, embedded brains GmbH

Address : Dornierstr. 4, D-82178 Puchheim, Germany
Phone   : +49 89 189 47 41-16
Fax     : +49 89 189 47 41-09
E-Mail  : sebastian.huber@embedded-brains.de
PGP     : Public key available on request.

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