gcc -flto=auto : function ‘uftrace___cyg_profile_func_exit’ redeclared as variable

[vitlav]

With -flto=auto optflag I got

  LINK     libmcount/libmcount.so
/tmp/.private/lav/RPM/BUILD/uftrace-0.10/libmcount/plthook.c:93:1: error: function ‘uftrace___cyg_profile_func_exit’ redeclared as variable
   93 | ALIAS_DECL(__cyg_profile_func_exit);
      | ^
/tmp/.private/lav/RPM/BUILD/uftrace-0.10/libmcount/mcount.c:1994:1: note: previously declared here
 1994 | UFTRACE_ALIAS(__cyg_profile_func_exit);
      | ^
/tmp/.private/lav/RPM/BUILD/uftrace-0.10/libmcount/plthook.c:92:1: error: function ‘uftrace___cyg_profile_func_enter’ redeclared as variable
   92 | ALIAS_DECL(__cyg_profile_func_enter);
      | ^
/tmp/.private/lav/RPM/BUILD/uftrace-0.10/libmcount/mcount.c:1988:1: note: previously declared here
 1988 | UFTRACE_ALIAS(__cyg_profile_func_enter);

pltook.c:
/* use weak reference for non-defined (arch-dependent) symbols */
#define ALIAS_DECL(_sym)  extern __weak void (*uftrace_##_sym)(void);

mcount.c:
#define UFTRACE_ALIAS(_func) void uftrace_##_func(void*, void*) __alias(_func)

[namhyung]

Thanks for the report, I'll take a look.

[honggyukim]

Hmm.. The error is also shown only with -flto and it looks tricky anyway.

Is there any special reason to use -flto=auto or -flto option when building uftrace?

[vitlav]

Hmm.. The error is also shown only with -flto and it looks tricky anyway.

Is there any special reason to use -flto=auto or -flto option when building uftrace?

That redeclation looks like a hidden bug for me.
There is no special reason to use LTO exclude the reason all vendors enable it by default:
https://fedoraproject.org/wiki/LTOByDefault
https://wiki.ubuntu.com/ToolChain/LTO
https://en.opensuse.org/openSUSE:LTO

[honggyukim]

Hmm.. we will think more about it. Thanks for reporting the issue.

[FantasqueX]

Same issue here when trying to package uftrace for ArchLinux. Temporarily disable LTO to solve the problem.

[amadio]

Related bug in Gentoo Linux: https://bugs.gentoo.org/858503

[namhyung]

I'm not sure but does the below help?

diff --git a/libmcount/plthook.c b/libmcount/plthook.c
index 5b5620bd6a..aa54bbc364 100644
--- a/libmcount/plthook.c
+++ b/libmcount/plthook.c
@@ -81,13 +81,14 @@ static void resolve_pltgot(struct plthook_data *pd, int idx)
 
 /* use weak reference for non-defined (arch-dependent) symbols */
 #define ALIAS_DECL(_sym) extern __weak void (*uftrace_##_sym)(void);
+#define ALIAS_DECL2(_sym) extern __weak void (*uftrace_##_sym)(void *, void *);
 
 ALIAS_DECL(mcount);
 ALIAS_DECL(_mcount);
 ALIAS_DECL(__fentry__);
 ALIAS_DECL(__gnu_mcount_nc);
-ALIAS_DECL(__cyg_profile_func_enter);
-ALIAS_DECL(__cyg_profile_func_exit);
+ALIAS_DECL2(__cyg_profile_func_enter);
+ALIAS_DECL2(__cyg_profile_func_exit);
 
 #define SKIP_SYM(func)                                                                             \
        {                                                                                          \

[amadio]

Unfortunately, no. I still get a compile error:

/tmp/portage/dev-util/uftrace-0.12/work/uftrace-0.12/libmcount/plthook.c:93:1: error: function ‘uftrace___cyg_profile_func_exit’ redeclared as variable
   93 | ALIAS_DECL2(__cyg_profile_func_exit);
      | ^
/tmp/portage/dev-util/uftrace-0.12/work/uftrace-0.12/libmcount/mcount.c:2004:1: note: previously declared here
 2004 | UFTRACE_ALIAS(__cyg_profile_func_exit);
      | ^
/tmp/portage/dev-util/uftrace-0.12/work/uftrace-0.12/libmcount/plthook.c:92:1: error: function ‘uftrace___cyg_profile_func_enter’ redeclared as variable
   92 | ALIAS_DECL2(__cyg_profile_func_enter);
      | ^
/tmp/portage/dev-util/uftrace-0.12/work/uftrace-0.12/libmcount/mcount.c:1998:1: note: previously declared here
 1998 | UFTRACE_ALIAS(__cyg_profile_func_enter);
      | ^
lto1: fatal error: errors during merging of translation units
compilation terminated.
lto-wrapper: fatal error: x86_64-pc-linux-gnu-gcc returned 1 exit status
compilation terminated.

If you want to reproduce this locally, try using

CFLAGS="-O2 -flto -Werror=odr -Werror=lto-type-mismatch -Werror=strict-aliasing"

when building.

[namhyung]

Thanks, I was able to reproduce it locally with your help. :)

This patch fixes the redeclaration error.

diff --git a/libmcount/plthook.c b/libmcount/plthook.c
index 5b5620bd6a..d9f1e8dd6a 100644
--- a/libmcount/plthook.c
+++ b/libmcount/plthook.c
@@ -80,14 +80,15 @@ static void resolve_pltgot(struct plthook_data *pd, int idx)
 }
 
 /* use weak reference for non-defined (arch-dependent) symbols */
-#define ALIAS_DECL(_sym) extern __weak void (*uftrace_##_sym)(void);
+#define ALIAS_DECL(_sym) extern __weak void uftrace_##_sym(void);
+#define ALIAS_DECL2(_sym) extern __weak void uftrace_##_sym(void *, void *);
 
 ALIAS_DECL(mcount);
 ALIAS_DECL(_mcount);
 ALIAS_DECL(__fentry__);
 ALIAS_DECL(__gnu_mcount_nc);
-ALIAS_DECL(__cyg_profile_func_enter);
-ALIAS_DECL(__cyg_profile_func_exit);
+ALIAS_DECL2(__cyg_profile_func_enter);
+ALIAS_DECL2(__cyg_profile_func_exit);
 
 #define SKIP_SYM(func)                                                                             \
        {                                                                                          \

But it reveals another problem like below. :-(

$ make
  LINK     libmcount/libmcount.so
lto-wrapper: warning: using serial compilation of 3 LTRANS jobs
lto-wrapper: note: see the ‘-flto’ option documentation for more information
/usr/bin/ld: /tmp/ccKRh5HD.ltrans0.ltrans.o: in function `mcount_rstack_restore':
/home/namhyung/project/uftrace/libmcount/misc.c:128: undefined reference to `plthook_return'
/usr/bin/ld: /tmp/ccKRh5HD.ltrans0.ltrans.o: in function `mcount_rstack_reset':
/home/namhyung/project/uftrace/libmcount/misc.c:207: undefined reference to `plthook_return'
/usr/bin/ld: /tmp/ccKRh5HD.ltrans0.ltrans.o: in function `mcount_startup.part.0':
/home/namhyung/project/uftrace/libmcount/mcount.c:1843: undefined reference to `mcount_return'
/usr/bin/ld: /tmp/ccKRh5HD.ltrans2.ltrans.o: in function `mcount_setup_trampoline':
/home/namhyung/project/uftrace/arch/x86_64/mcount-dynamic.c:79: undefined reference to `__dentry__'
/usr/bin/ld: /home/namhyung/project/uftrace/arch/x86_64/mcount-dynamic.c:59: undefined reference to `__xray_entry'
/usr/bin/ld: /home/namhyung/project/uftrace/arch/x86_64/mcount-dynamic.c:64: undefined reference to `__xray_exit'
collect2: error: ld returned 1 exit status
make: *** [Makefile:261: /home/namhyung/project/uftrace/libmcount/libmcount.so] Error 1

[amadio]

I tried with 0.13.1 and this bug is still there.

[namhyung]

I'm still not sure if LTO supports partial linking (ld -r).