[PATCH v4 15/18] perf clang: Declare BPF functions for BPF scripts automatically

[Wang Nan]

Use Clang's OverlayFileSystem, add '-include' options to make builtin
clang define BPF functions. After this patch BPF script writer needn't
define BPF functions by their own.

Add -DBUILTIN_CLANG_DEFAULT_INCLUDE to builtin clang so when adopting
builtin clang BPF functions can be automatically defined, and keep
undefined when using external clang. Passing a
-UBUILTIN_CLANG_DEFAULT_INCLUDE to cancel this defaudefinition.

Test cases are updated to avoid redefinition of these functions.

Signed-off-by: Wang Nan <wangnan0@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxx>
Cc: He Kuang <hekuang@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Zefan Li <lizefan@xxxxxxxxxx>
Cc: pi3orama@xxxxxxx
---
 tools/perf/tests/bpf-script-example.c         | 18 +++++++++------
 tools/perf/tests/bpf-script-test-prologue.c   |  2 ++
 tools/perf/tests/bpf-script-test-relocation.c | 18 +++++++++------
 tools/perf/util/c++/clang.cpp                 | 33 ++++++++++++++++++++++++++-
 4 files changed, 56 insertions(+), 15 deletions(-)

diff --git a/tools/perf/tests/bpf-script-example.c b/tools/perf/tests/bpf-script-example.c
index ccbc19c..42dc341 100644
--- a/tools/perf/tests/bpf-script-example.c
+++ b/tools/perf/tests/bpf-script-example.c
@@ -8,13 +8,6 @@
 #endif
 #define BPF_ANY 0
 #define BPF_MAP_TYPE_ARRAY 2
-#define BPF_FUNC_map_lookup_elem 1
-#define BPF_FUNC_map_update_elem 2
-
-static void *(*bpf_map_lookup_elem)(void *map, void *key) =
-	(void *) BPF_FUNC_map_lookup_elem;
-static void *(*bpf_map_update_elem)(void *map, void *key, void *value, int flags) =
-	(void *) BPF_FUNC_map_update_elem;
 
 struct bpf_map_def {
 	unsigned int type;
@@ -24,6 +17,17 @@ struct bpf_map_def {
 };
 
 #define SEC(NAME) __attribute__((section(NAME), used))
+
+#ifndef BUILTIN_CLANG_DEFAULT_INCLUDE
+#define BPF_FUNC_map_lookup_elem 1
+#define BPF_FUNC_map_update_elem 2
+
+static void *(*bpf_map_lookup_elem)(void *map, void *key) =
+	(void *) BPF_FUNC_map_lookup_elem;
+static void *(*bpf_map_update_elem)(void *map, void *key, void *value, int flags) =
+	(void *) BPF_FUNC_map_update_elem;
+#endif
+
 struct bpf_map_def SEC("maps") flip_table = {
 	.type = BPF_MAP_TYPE_ARRAY,
 	.key_size = sizeof(int),
diff --git a/tools/perf/tests/bpf-script-test-prologue.c b/tools/perf/tests/bpf-script-test-prologue.c
index 7230e62..ada812b 100644
--- a/tools/perf/tests/bpf-script-test-prologue.c
+++ b/tools/perf/tests/bpf-script-test-prologue.c
@@ -13,8 +13,10 @@
 #define FMODE_READ		0x1
 #define FMODE_WRITE		0x2
 
+#ifndef BUILTIN_CLANG_DEFAULT_INCLUDE
 static void (*bpf_trace_printk)(const char *fmt, int fmt_size, ...) =
 	(void *) 6;
+#endif
 
 SEC("func=null_lseek file->f_mode offset orig")
 int bpf_func__null_lseek(void *ctx, int err, unsigned long f_mode,
diff --git a/tools/perf/tests/bpf-script-test-relocation.c b/tools/perf/tests/bpf-script-test-relocation.c
index 93af774..57c96a3 100644
--- a/tools/perf/tests/bpf-script-test-relocation.c
+++ b/tools/perf/tests/bpf-script-test-relocation.c
@@ -8,13 +8,6 @@
 #endif
 #define BPF_ANY 0
 #define BPF_MAP_TYPE_ARRAY 2
-#define BPF_FUNC_map_lookup_elem 1
-#define BPF_FUNC_map_update_elem 2
-
-static void *(*bpf_map_lookup_elem)(void *map, void *key) =
-	(void *) BPF_FUNC_map_lookup_elem;
-static void *(*bpf_map_update_elem)(void *map, void *key, void *value, int flags) =
-	(void *) BPF_FUNC_map_update_elem;
 
 struct bpf_map_def {
 	unsigned int type;
@@ -24,6 +17,17 @@ struct bpf_map_def {
 };
 
 #define SEC(NAME) __attribute__((section(NAME), used))
+
+#ifndef BUILTIN_CLANG_DEFAULT_INCLUDE
+#define BPF_FUNC_map_lookup_elem 1
+#define BPF_FUNC_map_update_elem 2
+
+static void *(*bpf_map_lookup_elem)(void *map, void *key) =
+	(void *) BPF_FUNC_map_lookup_elem;
+static void *(*bpf_map_update_elem)(void *map, void *key, void *value, int flags) =
+	(void *) BPF_FUNC_map_update_elem;
+#endif
+
 struct bpf_map_def SEC("maps") my_table = {
 	.type = BPF_MAP_TYPE_ARRAY,
 	.key_size = sizeof(int),
diff --git a/tools/perf/util/c++/clang.cpp b/tools/perf/util/c++/clang.cpp
index 1bd92ea..feb69ea 100644
--- a/tools/perf/util/c++/clang.cpp
+++ b/tools/perf/util/c++/clang.cpp
@@ -39,9 +39,17 @@
 #include "util-cxx.h"
 #include "perf-hooks.h"
 #include "jit-helpers.h"
+#include "clang-bpf-includes.h"
 
 namespace perf {
 
+static struct BPFHeader {
+	llvm::StringRef Path;
+	llvm::StringRef Content;
+} BPFHeaders[] = {
+	{"/virtual/bpf-funcs.h", clang_builtin_bpf_funcs_str},
+};
+
 static std::unique_ptr<llvm::LLVMContext> LLVMCtx;
 
 using namespace clang;
@@ -63,6 +71,11 @@ createCompilerInvocation(llvm::opt::ArgStringList CFlags, StringRef& Path,
 		"-x", "c"};
 
 	CCArgs.append(CFlags.begin(), CFlags.end());
+	for (BPFHeader &h : BPFHeaders) {
+		CCArgs.append(1, "-include");
+		CCArgs.append(1, h.Path.begin());
+	}
+
 	CompilerInvocation *CI = tooling::newInvocation(&Diags, CCArgs);
 
 	FrontendOptions& Opts = CI->getFrontendOpts();
@@ -71,6 +84,22 @@ createCompilerInvocation(llvm::opt::ArgStringList CFlags, StringRef& Path,
 	return CI;
 }
 
+static IntrusiveRefCntPtr<vfs::FileSystem>
+addBPFHeaders(IntrusiveRefCntPtr<vfs::FileSystem> VFS)
+{
+	using namespace vfs;
+
+	llvm::IntrusiveRefCntPtr<OverlayFileSystem> OverlayFS(
+			new OverlayFileSystem(VFS));
+	llvm::IntrusiveRefCntPtr<InMemoryFileSystem> MemFS(
+			new InMemoryFileSystem(true));
+	OverlayFS->pushOverlay(MemFS);
+
+	for (BPFHeader &h : BPFHeaders)
+		MemFS->addFile(h.Path, 0, llvm::MemoryBuffer::getMemBuffer(h.Content));
+	return OverlayFS;
+}
+
 static std::unique_ptr<PerfModule>
 getModuleFromSource(llvm::opt::ArgStringList CFlags,
 		    StringRef Path, IntrusiveRefCntPtr<vfs::FileSystem> VFS)
@@ -78,7 +107,8 @@ getModuleFromSource(llvm::opt::ArgStringList CFlags,
 	CompilerInstance Clang;
 	Clang.createDiagnostics();
 
-	Clang.setVirtualFileSystem(&*VFS);
+	IntrusiveRefCntPtr<vfs::FileSystem> OverlayVFS = addBPFHeaders(VFS);
+	Clang.setVirtualFileSystem(&*OverlayVFS);
 
 	IntrusiveRefCntPtr<CompilerInvocation> CI =
 		createCompilerInvocation(std::move(CFlags), Path,
@@ -366,6 +396,7 @@ public:
 	{
 		CFlags.push_back(KVerDef.c_str());
 		CFlags.push_back(NRCpusDef.c_str());
+		CFlags.push_back("-DBUILTIN_CLANG_DEFAULT_INCLUDE");
 
 		fillCFlagsFromString(CFlags, clang_opt);
 		fillCFlagsFromString(CFlags, kbuild_include_opts, true);
-- 
2.10.1