perf tools: Call clang to compile C source to object code

This is the core patch for supporting eBPF on-the-fly compiling, does
the following work:

 1. Search clang compiler using search_program().

 2. Run command template defined in llvm-bpf-cmd-template option in
    [llvm] config section using read_from_pipe(). Patch of clang and
    source code path is injected into shell command using environment
    variable using force_set_env().

  Commiter notice:

  When building with DEBUG=1 we get a compiler error that gets fixed with
  the same approach described in commit b236512280fb:

    perf kmem: Fix compiler warning about may be accessing uninitialized variable

    The last argument to strtok_r doesn't need to be initialized, its
    just a placeholder to make this routine reentrant, but gcc doesn't know
    about that and complains, breaking the build, fix it by setting it to
    NULL.

Signed-off-by: Wang Nan <wangnan0@huawei.com>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: David Ahern <dsahern@gmail.com>
Cc: He Kuang <hekuang@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kaixu Xia <xiakaixu@huawei.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama@163.com
Link: http://lkml.kernel.org/n/1436445342-1402-14-git-send-email-wangnan0@huawei.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

1 files changed, 226 insertions, 0 deletions

diff --git a/tools/perf/util/llvm-utils.c b/tools/perf/util/llvm-utils.c
index 472e8cd69361..5ae11249baad 100644
--- a/tools/perf/util/llvm-utils.c
+++ b/tools/perf/util/llvm-utils.c
@@ -43,3 +43,229 @@ int perf_llvm_config(const char *var, const char *value)
                 return -1;
         return 0;
 }
+
+static int
+search_program(const char *def, const char *name,
+               char *output)
+{
+        char *env, *path, *tmp = NULL;
+        char buf[PATH_MAX];
+        int ret;
+
+        output[0] = '\0';
+        if (def && def[0] != '\0') {
+                if (def[0] == '/') {
+                        if (access(def, F_OK) == 0) {
+                                strlcpy(output, def, PATH_MAX);
+                                return 0;
+                        }
+                } else if (def[0] != '\0')
+                        name = def;
+        }
+
+        env = getenv("PATH");
+        if (!env)
+                return -1;
+        env = strdup(env);
+        if (!env)
+                return -1;
+
+        ret = -ENOENT;
+        path = strtok_r(env, ":",  &tmp);
+        while (path) {
+                scnprintf(buf, sizeof(buf), "%s/%s", path, name);
+                if (access(buf, F_OK) == 0) {
+                        strlcpy(output, buf, PATH_MAX);
+                        ret = 0;
+                        break;
+                }
+                path = strtok_r(NULL, ":", &tmp);
+        }
+
+        free(env);
+        return ret;
+}
+
+#define READ_SIZE       4096
+static int
+read_from_pipe(const char *cmd, void **p_buf, size_t *p_read_sz)
+{
+        int err = 0;
+        void *buf = NULL;
+        FILE *file = NULL;
+        size_t read_sz = 0, buf_sz = 0;
+
+        file = popen(cmd, "r");
+        if (!file) {
+                pr_err("ERROR: unable to popen cmd: %s\n",
+                       strerror(errno));
+                return -EINVAL;
+        }
+
+        while (!feof(file) && !ferror(file)) {
+                /*
+                 * Make buf_sz always have obe byte extra space so we
+                 * can put '\0' there.
+                 */
+                if (buf_sz - read_sz < READ_SIZE + 1) {
+                        void *new_buf;
+
+                        buf_sz = read_sz + READ_SIZE + 1;
+                        new_buf = realloc(buf, buf_sz);
+
+                        if (!new_buf) {
+                                pr_err("ERROR: failed to realloc memory\n");
+                                err = -ENOMEM;
+                                goto errout;
+                        }
+
+                        buf = new_buf;
+                }
+                read_sz += fread(buf + read_sz, 1, READ_SIZE, file);
+        }
+
+        if (buf_sz - read_sz < 1) {
+                pr_err("ERROR: internal error\n");
+                err = -EINVAL;
+                goto errout;
+        }
+
+        if (ferror(file)) {
+                pr_err("ERROR: error occurred when reading from pipe: %s\n",
+                       strerror(errno));
+                err = -EIO;
+                goto errout;
+        }
+
+        err = WEXITSTATUS(pclose(file));
+        file = NULL;
+        if (err) {
+                err = -EINVAL;
+                goto errout;
+        }
+
+        /*
+         * If buf is string, give it terminal '\0' to make our life
+         * easier. If buf is not string, that '\0' is out of space
+         * indicated by read_sz so caller won't even notice it.
+         */
+        ((char *)buf)[read_sz] = '\0';
+
+        if (!p_buf)
+                free(buf);
+        else
+                *p_buf = buf;
+
+        if (p_read_sz)
+                *p_read_sz = read_sz;
+        return 0;
+
+errout:
+        if (file)
+                pclose(file);
+        free(buf);
+        if (p_buf)
+                *p_buf = NULL;
+        if (p_read_sz)
+                *p_read_sz = 0;
+        return err;
+}
+
+static inline void
+force_set_env(const char *var, const char *value)
+{
+        if (value) {
+                setenv(var, value, 1);
+                pr_debug("set env: %s=%s\n", var, value);
+        } else {
+                unsetenv(var);
+                pr_debug("unset env: %s\n", var);
+        }
+}
+
+static void
+version_notice(void)
+{
+        pr_err(
+"     \tLLVM 3.7 or newer is required. Which can be found from http://llvm.org\n"
+"     \tYou may want to try git trunk:\n"
+"     \t\tgit clone http://llvm.org/git/llvm.git\n"
+"     \t\t     and\n"
+"     \t\tgit clone http://llvm.org/git/clang.git\n\n"
+"     \tOr fetch the latest clang/llvm 3.7 from pre-built llvm packages for\n"
+"     \tdebian/ubuntu:\n"
+"     \t\thttp://llvm.org/apt\n\n"
+"     \tIf you are using old version of clang, change 'clang-bpf-cmd-template'\n"
+"     \toption in [llvm] section of ~/.perfconfig to:\n\n"
+"     \t  \"$CLANG_EXEC $CLANG_OPTIONS $KERNEL_INC_OPTIONS \\\n"
+"     \t     -working-directory $WORKING_DIR -c $CLANG_SOURCE \\\n"
+"     \t     -emit-llvm -o - | /path/to/llc -march=bpf -filetype=obj -o -\"\n"
+"     \t(Replace /path/to/llc with path to your llc)\n\n"
+);
+}
+
+int llvm__compile_bpf(const char *path, void **p_obj_buf,
+                      size_t *p_obj_buf_sz)
+{
+        int err;
+        char clang_path[PATH_MAX];
+        const char *clang_opt = llvm_param.clang_opt;
+        const char *template = llvm_param.clang_bpf_cmd_template;
+        void *obj_buf = NULL;
+        size_t obj_buf_sz;
+
+        if (!template)
+                template = CLANG_BPF_CMD_DEFAULT_TEMPLATE;
+
+        err = search_program(llvm_param.clang_path,
+                             "clang", clang_path);
+        if (err) {
+                pr_err(
+"ERROR:\tunable to find clang.\n"
+"Hint:\tTry to install latest clang/llvm to support BPF. Check your $PATH\n"
+"     \tand 'clang-path' option in [llvm] section of ~/.perfconfig.\n");
+                version_notice();
+                return -ENOENT;
+        }
+
+        force_set_env("CLANG_EXEC", clang_path);
+        force_set_env("CLANG_OPTIONS", clang_opt);
+        force_set_env("KERNEL_INC_OPTIONS", NULL);
+        force_set_env("WORKING_DIR", ".");
+
+        /*
+         * Since we may reset clang's working dir, path of source file
+         * should be transferred into absolute path, except we want
+         * stdin to be source file (testing).
+         */
+        force_set_env("CLANG_SOURCE",
+                      (path[0] == '-') ? path :
+                      make_nonrelative_path(path));
+
+        pr_debug("llvm compiling command template: %s\n", template);
+        err = read_from_pipe(template, &obj_buf, &obj_buf_sz);
+        if (err) {
+                pr_err("ERROR:\tunable to compile %s\n", path);
+                pr_err("Hint:\tCheck error message shown above.\n");
+                pr_err("Hint:\tYou can also pre-compile it into .o using:\n");
+                pr_err("     \t\tclang -target bpf -O2 -c %s\n", path);
+                pr_err("     \twith proper -I and -D options.\n");
+                goto errout;
+        }
+
+        if (!p_obj_buf)
+                free(obj_buf);
+        else
+                *p_obj_buf = obj_buf;
+
+        if (p_obj_buf_sz)
+                *p_obj_buf_sz = obj_buf_sz;
+        return 0;
+errout:
+        free(obj_buf);
+        if (p_obj_buf)
+                *p_obj_buf = NULL;
+        if (p_obj_buf_sz)
+                *p_obj_buf_sz = 0;
+        return err;
+}