Unify vmlinux and BTF location list

vmlinux is used for both symbol resolution and BTF. Manage the location
list in one place.

src/attached_probe.cpp

@@ -386,42 +386,39 @@ void AttachedProbe::resolve_offset_uprobe(bool safe_mode)
       probe_.path, symbol, sym_offset, func_offset, safe_mode, probe_.type);
 }
 
-static std::string find_vmlinux()
+// find vmlinux file containing the given symbol information
+static std::string find_vmlinux(const struct vmlinux_location *locs,
+                                struct symbol &sym)
 {
-  char *path = std::getenv("BPFTRACE_VMLINUX");
-  if (path)
-    return path;
-
+  struct bcc_symbol_option option = {};
+  option.use_debug_file = 0;
+  option.use_symbol_type = BCC_SYM_ALL_TYPES;
   struct utsname buf;
-  uname(&buf);
 
-  // based on btf_location in btf.cpp
-  const char *vmlinux_locs[] = {
-    "/boot/vmlinux-%1$s",
-    "/lib/modules/%1$s/vmlinux-%1$s",
-    "/lib/modules/%1$s/build/vmlinux",
-    "/usr/lib/modules/%1$s/kernel/vmlinux",
-    "/usr/lib/debug/boot/vmlinux-%1$s",
-    "/usr/lib/debug/boot/vmlinux-%1$s.debug",
-    "/usr/lib/debug/lib/modules/%1$s/vmlinux",
-    nullptr,
-  };
+  uname(&buf);
 
-  for (int i = 0; vmlinux_locs[i]; i++)
+  for (int i = 0; locs[i].path; i++)
   {
+    if (locs[i].raw)
+      continue; // This file is for BTF. skip
     char path[PATH_MAX + 1];
-    snprintf(path, PATH_MAX, vmlinux_locs[i], buf.release);
+    snprintf(path, PATH_MAX, locs[i].path, buf.release);
     if (access(path, R_OK))
       continue;
-    return path;
+    bcc_elf_foreach_sym(path, sym_name_cb, &option, &sym);
+    if (sym.start)
+    {
+      if (bt_verbose)
+        std::cout << "vmlinux: using " << path << std::endl;
+      return path;
+    }
   }
 
   return "";
 }
 
 void AttachedProbe::resolve_offset_kprobe(bool safe_mode)
 {
-  struct bcc_symbol_option option = {};
   struct symbol sym = {};
   std::string &symbol = probe_.attach_point;
   uint64_t func_offset = probe_.func_offset;
@@ -435,16 +432,25 @@ void AttachedProbe::resolve_offset_kprobe(bool safe_mode)
     return;
 
   sym.name = symbol;
-  option.use_debug_file = 0;
-  option.use_symbol_type = BCC_SYM_ALL_TYPES;
+  const struct vmlinux_location *locs = vmlinux_locs;
+  struct vmlinux_location locs_env[] = {
+    { nullptr, true },
+    { nullptr, false },
+  };
+  char *env_path = std::getenv("BPFTRACE_VMLINUX");
+  if (env_path)
+  {
+    locs_env[0].path = env_path;
+    locs = locs_env;
+  }
 
-  std::string path = find_vmlinux();
+  std::string path = find_vmlinux(locs, sym);
   if (path.empty())
   {
     if (safe_mode)
     {
       std::stringstream buf;
-      buf << "Could not find vmlinux to check the offset.";
+      buf << "Could not resolve symbol " << symbol << ".";
       buf << " Use BPFTRACE_VMLINUX env variable to specify vmlinux path.";
 #ifdef HAVE_UNSAFE_PROBE
       buf << " Use --unsafe to skip the userspace check.";
@@ -458,17 +464,11 @@ void AttachedProbe::resolve_offset_kprobe(bool safe_mode)
     {
       // linux kernel checks alignment, but not the function bounds
       if (bt_verbose)
-        std::cout << "No vmlinux found. Skip offset checking." << std::endl;
+        std::cout << "Could not resolve symbol " << symbol
+                  << ". Skip offset checking." << std::endl;
       return;
     }
   }
-  if (bt_verbose)
-    std::cout << "vmlinux: using " << path << std::endl;
-  bcc_elf_foreach_sym(path.c_str(), sym_name_cb, &option, &sym);
-
-  if (!sym.start)
-    throw std::runtime_error("Could not resolve symbol: " + path + ":" +
-                             symbol);
 
   if (func_offset >= sym.size)
     throw std::runtime_error("Offset outside the function bounds ('" + symbol +

src/btf.cpp

@@ -1,15 +1,16 @@
+#include "btf.h"
+#include "bpftrace.h"
+#include "types.h"
+#include "utils.h"
+#include <fcntl.h>
 #include <iostream>
+#include <linux/limits.h>
 #include <regex>
-#include <sys/types.h>
+#include <string.h>
 #include <sys/stat.h>
-#include <fcntl.h>
-#include <unistd.h>
+#include <sys/types.h>
 #include <sys/utsname.h>
-#include <string.h>
-#include <linux/limits.h>
-#include "btf.h"
-#include "types.h"
-#include "bpftrace.h"
+#include <unistd.h>
 
 #ifdef HAVE_LIBBPF_BTF_DUMP
 #include <linux/bpf.h>
@@ -19,11 +20,6 @@
 
 namespace bpftrace {
 
-struct btf_location {
-  const char *path; // path with possible "%s" format to be replaced current release
-  bool        raw;  // file is either as ELF (false) or raw BTF data (true)
-};
-
 static unsigned char *get_data(const char *file, ssize_t *sizep)
 {
   struct stat st;
@@ -88,7 +84,7 @@ static int libbpf_print(enum libbpf_print_level level, const char *msg, va_list
   return vfprintf(stderr, msg, ap);
 }
 
-static struct btf *btf_open(struct btf_location *locs)
+static struct btf *btf_open(const struct vmlinux_location *locs)
 {
   struct utsname buf;
 
@@ -135,36 +131,20 @@ static struct btf *btf_open(struct btf_location *locs)
 
 BTF::BTF(void) : btf(nullptr), state(NODATA)
 {
-  // 'borrowed' from libbpf's bpf_core_find_kernel_btf
-  // from Andrii Nakryiko
-  struct btf_location locs_normal[] =
-  {
-    { "/sys/kernel/btf/vmlinux",                 true  },
-    { "/boot/vmlinux-%1$s",                      false },
-    { "/lib/modules/%1$s/vmlinux-%1$s",          false },
-    { "/lib/modules/%1$s/build/vmlinux",         false },
-    { "/usr/lib/modules/%1$s/kernel/vmlinux",    false },
-    { "/usr/lib/debug/boot/vmlinux-%1$s",        false },
-    { "/usr/lib/debug/boot/vmlinux-%1$s.debug",  false },
-    { "/usr/lib/debug/lib/modules/%1$s/vmlinux", false },
-    { nullptr, false },
-  };
-
-  struct btf_location locs_test[] =
-  {
-    { nullptr, true  },
+  struct vmlinux_location locs_env[] = {
+    { nullptr, true },
     { nullptr, false },
   };
 
-  struct btf_location *locs = locs_normal;
+  const struct vmlinux_location *locs = vmlinux_locs;
 
   // Try to get BTF file from BPFTRACE_BTF env
   char *path = std::getenv("BPFTRACE_BTF");
 
   if (path)
   {
-    locs_test[0].path = path;
-    locs = locs_test;
+    locs_env[0].path = path;
+    locs = locs_env;
   }
 
   btf = btf_open(locs);

src/utils.cpp

@@ -74,6 +74,20 @@ std::vector<std::string> expand_wildcard_paths(const std::vector<std::string>& p
 
 namespace bpftrace {
 
+//'borrowed' from libbpf's bpf_core_find_kernel_btf
+// from Andrii Nakryiko
+const struct vmlinux_location vmlinux_locs[] = {
+  { "/sys/kernel/btf/vmlinux", true },
+  { "/boot/vmlinux-%1$s", false },
+  { "/lib/modules/%1$s/vmlinux-%1$s", false },
+  { "/lib/modules/%1$s/build/vmlinux", false },
+  { "/usr/lib/modules/%1$s/kernel/vmlinux", false },
+  { "/usr/lib/debug/boot/vmlinux-%1$s", false },
+  { "/usr/lib/debug/boot/vmlinux-%1$s.debug", false },
+  { "/usr/lib/debug/lib/modules/%1$s/vmlinux", false },
+  { nullptr, false },
+};
+
 static bool provider_cache_loaded = false;
 
 // Maps all providers of pid to vector of tracepoints on that provider

src/utils.h

@@ -10,6 +10,14 @@
 
 namespace bpftrace {
 
+struct vmlinux_location
+{
+  const char *path; // path with possible "%s" format to be replaced current
+                    // release
+  bool raw;         // file is either as ELF (false) or raw BTF data (true)
+};
+extern const struct vmlinux_location vmlinux_locs[];
+
 typedef enum _USDT_TUPLE_ORDER_
 {
   USDT_PATH_INDEX,