arm64: define the KASAN_SHADOW_SCALE_SHIFT macro

arm64 defines this macro from Makefile instead of defining it in a
header file as is the case for other architectures. Since we're not
running make, we need to define the macro manually via CFLAGS.

The value definition is taken from kernel's arch/arm64/Makefile and it
depends on the running kernel configuration.

This fixes the runqlat.bt tcpdrop.bt, and undump.bt tools on
aarch64+debug kernel which previously failed with:

    # /usr/share/bpftrace/tools/runqlat.bt
    [...]/source/arch/arm64/include/asm/memory.h:300:9: error: use of undeclared identifier 'KASAN_SHADOW_SCALE_SHIFT'
    [...]

CHANGELOG.md

@@ -25,6 +25,8 @@ and this project adheres to
   - [#2521](https://github.com/iovisor/bpftrace/pull/2521)
 - Respect BPFTRACE_STRLEN environment variable for all strings
   - [#2545](https://github.com/iovisor/bpftrace/pull/2545)
+- arm64: define the KASAN_SHADOW_SCALE_SHIFT macro
+  - [#2518](https://github.com/iovisor/bpftrace/pull/2518)
 #### Docs
 #### Tools
 

src/main.cpp

@@ -369,7 +369,8 @@ static std::optional<struct timespec> get_boottime()
     kobj = std::get<1>(kdirs);
 
     if (ksrc != "")
-      extra_flags = get_kernel_cflags(utsname.machine, ksrc, kobj);
+      extra_flags = get_kernel_cflags(
+          utsname.machine, ksrc, kobj, bpftrace.kconfig);
   }
   extra_flags.push_back("-include");
   extra_flags.push_back(CLANG_WORKAROUNDS_H);

src/utils.cpp

@@ -228,7 +228,6 @@ KConfig::KConfig()
   }
 }
 
-
 bool get_uint64_env_var(const std::string &str, uint64_t &dest)
 {
   if (const char* env_p = std::getenv(str.c_str()))
@@ -365,10 +364,10 @@ std::vector<int> get_possible_cpus()
   return read_cpu_range("/sys/devices/system/cpu/possible");
 }
 
-std::vector<std::string> get_kernel_cflags(
-    const char* uname_machine,
-    const std::string& ksrc,
-    const std::string& kobj)
+std::vector<std::string> get_kernel_cflags(const char *uname_machine,
+                                           const std::string &ksrc,
+                                           const std::string &kobj,
+                                           const KConfig &kconfig)
 {
   std::vector<std::string> cflags;
   std::string arch = uname_machine;
@@ -434,6 +433,20 @@ std::vector<std::string> get_kernel_cflags(
     cflags.push_back("-D__LINUX_ARM_ARCH__=7");
   }
 
+  if (arch == "arm64")
+  {
+    // arm64 defines KASAN_SHADOW_SCALE_SHIFT in a Makefile instead of defining
+    // it in a header file. Since we're not executing make, we need to set the
+    // value manually (values are taken from arch/arm64/Makefile).
+    if (kconfig.has_value("CONFIG_KASAN", "y"))
+    {
+      if (kconfig.has_value("CONFIG_KASAN_SW_TAGS", "y"))
+        cflags.push_back("-DKASAN_SHADOW_SCALE_SHIFT=4");
+      else
+        cflags.push_back("-DKASAN_SHADOW_SCALE_SHIFT=3");
+    }
+  }
+
   return cflags;
 }
 

src/utils.h

@@ -178,7 +178,8 @@ std::tuple<std::string, std::string> get_kernel_dirs(
     bool unpack_kheaders);
 std::vector<std::string> get_kernel_cflags(const char *uname_machine,
                                            const std::string &ksrc,
-                                           const std::string &kobj);
+                                           const std::string &kobj,
+                                           const KConfig &kconfig);
 std::string get_cgroup_path_in_hierarchy(uint64_t cgroupid,
                                          std::string base_path);
 std::vector<std::pair<std::string, std::string>> get_cgroup_hierarchy_roots();