[PATCH] perf unwind: Fix compile error for static cross build

[He Kuang <hekuang@huawei.com>]

Build failure for static cross-compiling on aarch64, with
libunwind-x86 provided.

$ file ./libunwind_for_x86_on_aarch64/lib/libunwind-x86.so.8.0.1

  libunwind-x86.so.8.0.1: ELF 64-bit LSB shared object, ARM aarch64,
  version 1 (SYSV), dynamically linked, not stripped

$ make LDFLAGS=-static LIBUNWIND_DIR=./libunwind_for_x86_on_aarch64
  ARCH=aarch64 CROSS_COMPILE=aarch64-buildroot-linux-gnu-

  ~/libperf.a(libperf-in.o): In function `find_proc_info':
  :(.text+0xae4ac): undefined reference to `_Ux86_dwarf_search_unwind_table'
  ~/libperf.a(libperf-in.o): In function `_unwind__prepare_access':
  :(.text+0xaedd0): undefined reference to `_Ux86_create_addr_space'
  :(.text+0xaee24): undefined reference to `_Ux86_set_caching_policy'
  ~/libperf.a(libperf-in.o): In function `_unwind__flush_access':
  :(.text+0xaee98): undefined reference to `_Ux86_flush_cache'
  ~/libperf.a(libperf-in.o): In function `_unwind__finish_access':
  :(.text+0xaef08): undefined reference to `_Ux86_destroy_addr_space'
  ~/libperf.a(libperf-in.o): In function `get_entries':
  :(.text+0xaf148): undefined reference to `_Ux86_init_remote'
  :(.text+0xaf184): undefined reference to `_Ux86_get_reg'
  :(.text+0xaf1a4): undefined reference to `_Ux86_step'
  collect2: error: ld returned 1 exit status
  Makefile.perf:350: recipe for target '~/perf' failed
  make[1]: *** [~/perf] Error 1
  Makefile:68: recipe for target 'all' failed
  make: *** [all] Error 2

This is because the remote libunwind library detected are not appended
to EXTLIBS variable, which will be included between 'start-group' and
'end-group' when linking.

The existing variable LIBUNWIND_LIBS is assigned to libs for local
unwind, this patch introduces a new variable EXTLIBS_LIBUNWIND for
storing remote libunwind libraries instead.

Signed-off-by: He Kuang <hekuang@huawei.com>
---
 tools/perf/config/Makefile | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/tools/perf/config/Makefile b/tools/perf/config/Makefile
index 098874b..80018fe 100644
--- a/tools/perf/config/Makefile
+++ b/tools/perf/config/Makefile
@@ -365,6 +365,7 @@ ifndef NO_LIBUNWIND
     $(call detected,CONFIG_LIBUNWIND_X86)
     CFLAGS += -DHAVE_LIBUNWIND_X86_SUPPORT
     LDFLAGS += -lunwind-x86
+    EXTLIBS_LIBUNWIND += -lunwind-x86
     have_libunwind = 1
   endif
 
@@ -372,6 +373,7 @@ ifndef NO_LIBUNWIND
     $(call detected,CONFIG_LIBUNWIND_AARCH64)
     CFLAGS += -DHAVE_LIBUNWIND_AARCH64_SUPPORT
     LDFLAGS += -lunwind-aarch64
+    EXTLIBS_LIBUNWIND += -lunwind-aarch64
     have_libunwind = 1
     $(call feature_check,libunwind-debug-frame-aarch64)
     ifneq ($(feature-libunwind-debug-frame-aarch64), 1)
@@ -449,6 +451,7 @@ ifndef NO_LIBUNWIND
   CFLAGS  += -DHAVE_LIBUNWIND_SUPPORT
   CFLAGS  += $(LIBUNWIND_CFLAGS)
   LDFLAGS += $(LIBUNWIND_LDFLAGS)
+  EXTLIBS += $(EXTLIBS_LIBUNWIND)
 endif
 
 ifndef NO_LIBAUDIT
-- 
1.8.5.2