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Date:   Tue, 18 Aug 2020 14:59:08 -0700
From:   Andrii Nakryiko <andriin@...com>
To:     <bpf@...r.kernel.org>, <netdev@...r.kernel.org>, <ast@...com>,
        <daniel@...earbox.net>
CC:     <andrii.nakryiko@...il.com>, <kernel-team@...com>,
        Andrii Nakryiko <andriin@...com>
Subject: [PATCH bpf-next 4/4] tools: remove feature-libelf-mmap feature detection

It's trivial to handle missing ELF_C_MMAP_READ support in libelf the way that
objtool has solved it in
("774bec3fddcc objtool: Add fallback from ELF_C_READ_MMAP to ELF_C_READ").

So instead of having an entire feature detector for that, just do what objtool
does for perf and libbpf. And keep their Makefiles a bit simpler.

Signed-off-by: Andrii Nakryiko <andriin@...com>
---
 tools/build/Makefile.feature           |  1 -
 tools/build/feature/Makefile           |  4 ----
 tools/build/feature/test-all.c         |  4 ----
 tools/build/feature/test-libelf-mmap.c |  9 ---------
 tools/lib/bpf/Makefile                 |  6 +-----
 tools/lib/bpf/libbpf.c                 | 14 ++++++--------
 tools/perf/Makefile.config             |  4 ----
 tools/perf/util/symbol.h               |  2 +-
 8 files changed, 8 insertions(+), 36 deletions(-)
 delete mode 100644 tools/build/feature/test-libelf-mmap.c

diff --git a/tools/build/Makefile.feature b/tools/build/Makefile.feature
index c1daf4d57518..38415d251075 100644
--- a/tools/build/Makefile.feature
+++ b/tools/build/Makefile.feature
@@ -46,7 +46,6 @@ FEATURE_TESTS_BASIC :=                  \
         libelf-getphdrnum               \
         libelf-gelf_getnote             \
         libelf-getshdrstrndx            \
-        libelf-mmap                     \
         libnuma                         \
         numa_num_possible_cpus          \
         libperl                         \
diff --git a/tools/build/feature/Makefile b/tools/build/feature/Makefile
index d220fe952747..b2a2347c67ed 100644
--- a/tools/build/feature/Makefile
+++ b/tools/build/feature/Makefile
@@ -25,7 +25,6 @@ FILES=                                          \
          test-libelf-getphdrnum.bin             \
          test-libelf-gelf_getnote.bin           \
          test-libelf-getshdrstrndx.bin          \
-         test-libelf-mmap.bin                   \
          test-libdebuginfod.bin                 \
          test-libnuma.bin                       \
          test-numa_num_possible_cpus.bin        \
@@ -146,9 +145,6 @@ $(OUTPUT)test-dwarf.bin:
 $(OUTPUT)test-dwarf_getlocations.bin:
 	$(BUILD) $(DWARFLIBS)
 
-$(OUTPUT)test-libelf-mmap.bin:
-	$(BUILD) -lelf
-
 $(OUTPUT)test-libelf-getphdrnum.bin:
 	$(BUILD) -lelf
 
diff --git a/tools/build/feature/test-all.c b/tools/build/feature/test-all.c
index 5479e543b194..5284e6e9c756 100644
--- a/tools/build/feature/test-all.c
+++ b/tools/build/feature/test-all.c
@@ -30,10 +30,6 @@
 # include "test-libelf.c"
 #undef main
 
-#define main main_test_libelf_mmap
-# include "test-libelf-mmap.c"
-#undef main
-
 #define main main_test_get_current_dir_name
 # include "test-get_current_dir_name.c"
 #undef main
diff --git a/tools/build/feature/test-libelf-mmap.c b/tools/build/feature/test-libelf-mmap.c
deleted file mode 100644
index 2c3ef81affe2..000000000000
--- a/tools/build/feature/test-libelf-mmap.c
+++ /dev/null
@@ -1,9 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-#include <libelf.h>
-
-int main(void)
-{
-	Elf *elf = elf_begin(0, ELF_C_READ_MMAP, 0);
-
-	return (long)elf;
-}
diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
index 99796cfc1b9b..eb193bdf43f9 100644
--- a/tools/lib/bpf/Makefile
+++ b/tools/lib/bpf/Makefile
@@ -56,7 +56,7 @@ ifndef VERBOSE
 endif
 
 FEATURE_USER = .libbpf
-FEATURE_TESTS = libelf libelf-mmap zlib bpf
+FEATURE_TESTS = libelf zlib bpf
 FEATURE_DISPLAY = libelf zlib bpf
 
 INCLUDES = -I. -I$(srctree)/tools/include -I$(srctree)/tools/arch/$(ARCH)/include/uapi -I$(srctree)/tools/include/uapi
@@ -98,10 +98,6 @@ else
   CFLAGS := -g -Wall
 endif
 
-ifeq ($(feature-libelf-mmap), 1)
-  override CFLAGS += -DHAVE_LIBELF_MMAP_SUPPORT
-endif
-
 # Append required CFLAGS
 override CFLAGS += $(EXTRA_WARNINGS)
 override CFLAGS += -Werror -Wall
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index f3f4963d6ba4..78d883c5a8f7 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -150,12 +150,6 @@ static void pr_perm_msg(int err)
 	___err; })
 #endif
 
-#ifdef HAVE_LIBELF_MMAP_SUPPORT
-# define LIBBPF_ELF_C_READ_MMAP ELF_C_READ_MMAP
-#else
-# define LIBBPF_ELF_C_READ_MMAP ELF_C_READ
-#endif
-
 static inline __u64 ptr_to_u64(const void *ptr)
 {
 	return (__u64) (unsigned long) ptr;
@@ -1062,6 +1056,11 @@ static void bpf_object__elf_finish(struct bpf_object *obj)
 	obj->efile.obj_buf_sz = 0;
 }
 
+/* if libelf is old and doesn't support mmap(), fall back to read() */
+#ifndef ELF_C_READ_MMAP
+#define ELF_C_READ_MMAP ELF_C_READ
+#endif
+
 static int bpf_object__elf_init(struct bpf_object *obj)
 {
 	int err = 0;
@@ -1090,8 +1089,7 @@ static int bpf_object__elf_init(struct bpf_object *obj)
 			return err;
 		}
 
-		obj->efile.elf = elf_begin(obj->efile.fd,
-					   LIBBPF_ELF_C_READ_MMAP, NULL);
+		obj->efile.elf = elf_begin(obj->efile.fd, ELF_C_READ_MMAP, NULL);
 	}
 
 	if (!obj->efile.elf) {
diff --git a/tools/perf/Makefile.config b/tools/perf/Makefile.config
index 190be4fa5c21..81bb099f6f06 100644
--- a/tools/perf/Makefile.config
+++ b/tools/perf/Makefile.config
@@ -483,10 +483,6 @@ ifndef NO_LIBELF
   EXTLIBS += -lelf
   $(call detected,CONFIG_LIBELF)
 
-  ifeq ($(feature-libelf-mmap), 1)
-    CFLAGS += -DHAVE_LIBELF_MMAP_SUPPORT
-  endif
-
   ifeq ($(feature-libelf-getphdrnum), 1)
     CFLAGS += -DHAVE_ELF_GETPHDRNUM_SUPPORT
   endif
diff --git a/tools/perf/util/symbol.h b/tools/perf/util/symbol.h
index ff4f4c47e148..03e264a27cd3 100644
--- a/tools/perf/util/symbol.h
+++ b/tools/perf/util/symbol.h
@@ -28,7 +28,7 @@ struct option;
  * libelf 0.8.x and earlier do not support ELF_C_READ_MMAP;
  * for newer versions we can use mmap to reduce memory usage:
  */
-#ifdef HAVE_LIBELF_MMAP_SUPPORT
+#ifdef ELF_C_READ_MMAP
 # define PERF_ELF_C_READ_MMAP ELF_C_READ_MMAP
 #else
 # define PERF_ELF_C_READ_MMAP ELF_C_READ
-- 
2.24.1

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