[PATCH v3 1/3] perf: build: Fix static compilation error when libdw is not installed

[Yang Jihong]

If libdw is not installed in build environment, the output of
'pkg-config --modversion libdw' is empty, causing LIBDW_VERSION_2
to be empty and the shell test will have the following error:

  /bin/sh: 1: test: -lt: unexpected operator

Before:

  $ pkg-config --modversion libdw
  Package libdw was not found in the pkg-config search path.
  Perhaps you should add the directory containing `libdw.pc'
  to the PKG_CONFIG_PATH environment variable
  No package 'libdw' found
  $ make LDFLAGS=-static -j16
    BUILD:   Doing 'make -j20' parallel build
  <SNIP>
  Package libdw was not found in the pkg-config search path.
  Perhaps you should add the directory containing `libdw.pc'
  to the PKG_CONFIG_PATH environment variable
  No package 'libdw' found
  /bin/sh: 1: test: -lt: unexpected operator

After:

  1. libdw is not installed:

  $ pkg-config --modversion libdw
  Package libdw was not found in the pkg-config search path.
  Perhaps you should add the directory containing `libdw.pc'
  to the PKG_CONFIG_PATH environment variable
  No package 'libdw' found
  $ make LDFLAGS=-static -j16
    BUILD:   Doing 'make -j20' parallel build
  <SNIP>
  Package libdw was not found in the pkg-config search path.
  Perhaps you should add the directory containing `libdw.pc'
  to the PKG_CONFIG_PATH environment variable
  No package 'libdw' found
  Makefile.config:473: No libdw DWARF unwind found, Please install elfutils-devel/libdw-dev >= 0.158 and/or set LIBDW_DIR

  2. libdw version is lower than 0.177

  $ pkg-config --modversion libdw
  0.176
  $ make LDFLAGS=-static -j16
    BUILD:   Doing 'make -j20' parallel build
  <SNIP>

  Auto-detecting system features:
  ...                                   dwarf: [ on  ]
  <SNIP>
    INSTALL libsubcmd_headers
    INSTALL libapi_headers
    INSTALL libperf_headers
    INSTALL libsymbol_headers
    INSTALL libbpf_headers
    LINK    perf

  3. libdw version is higher than 0.177

  $ pkg-config --modversion libdw
  0.186
  $ make LDFLAGS=-static -j16
    BUILD:   Doing 'make -j20' parallel build
  <SNIP>

  Auto-detecting system features:
  ...                                   dwarf: [ on  ]
  <SNIP>
    CC      util/bpf-utils.o
    CC      util/pfm.o
    LD      util/perf-util-in.o
    LD      perf-util-in.o
    AR      libperf-util.a
    LINK    perf

Fixes: 536661da6ea1 ("perf: build: Only link libebl.a for old libdw")
Signed-off-by: Yang Jihong <yangjihong@xxxxxxxxxxxxx>
---
 tools/build/feature/Makefile | 2 +-
 tools/perf/Makefile.config   | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/build/feature/Makefile b/tools/build/feature/Makefile
index 12796808f07a..a0167244b2f7 100644
--- a/tools/build/feature/Makefile
+++ b/tools/build/feature/Makefile
@@ -172,7 +172,7 @@ DWARFLIBS := -ldw
 ifeq ($(findstring -static,${LDFLAGS}),-static)
   DWARFLIBS += -lelf -lz -llzma -lbz2 -lzstd
 
-  LIBDW_VERSION := $(shell $(PKG_CONFIG) --modversion libdw)
+  LIBDW_VERSION := $(shell $(PKG_CONFIG) --modversion libdw).0.0
   LIBDW_VERSION_1 := $(word 1, $(subst ., ,$(LIBDW_VERSION)))
   LIBDW_VERSION_2 := $(word 2, $(subst ., ,$(LIBDW_VERSION)))
 
diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
index fa679db61f62..b452794c763a 100644
--- a/tools/perf/Makefile.config
+++ b/tools/perf/Makefile.config
@@ -154,7 +154,7 @@ DWARFLIBS := -ldw
 ifeq ($(findstring -static,${LDFLAGS}),-static)
   DWARFLIBS += -lelf -ldl -lz -llzma -lbz2 -lzstd
 
-  LIBDW_VERSION := $(shell $(PKG_CONFIG) --modversion libdw)
+  LIBDW_VERSION := $(shell $(PKG_CONFIG) --modversion libdw).0.0
   LIBDW_VERSION_1 := $(word 1, $(subst ., ,$(LIBDW_VERSION)))
   LIBDW_VERSION_2 := $(word 2, $(subst ., ,$(LIBDW_VERSION)))
 
-- 
2.25.1