[compiler-rt] d75a565 - [asan] Always skip first object from dl_iterate_phdr

[Fangrui Song via llvm-commits]

Author: Michael Forney
Date: 2022-02-11T14:49:25-08:00
New Revision: d75a5650dbdc595f836db4711f2a480f87243593

URL: https://github.com/llvm/llvm-project/commit/d75a5650dbdc595f836db4711f2a480f87243593
DIFF: https://github.com/llvm/llvm-project/commit/d75a5650dbdc595f836db4711f2a480f87243593.diff

LOG: [asan] Always skip first object from dl_iterate_phdr

All platforms return the main executable as the first dl_phdr_info.
FreeBSD, NetBSD, Solaris, and Linux-musl place the executable name
in the dlpi_name field of this entry. It appears that only Linux-glibc
uses the empty string.

To make this work generically on all platforms, unconditionally skip the first
object (like is currently done for FreeBSD and NetBSD). This fixes first DSO
detection on Linux-musl with clang -shared-libsan/-shared-libasan and GCC's
default. It also would likely fix detection on Solaris/Illumos if it were to
gain PIE support (since dlpi_addr would not be NULL).

Additionally, only skip the Linux VDSO on linux.

Finally, use the empty string as the "seen first dl_phdr_info"
marker rather than (char *)-1. If there was no other object, we
would try to dereference it for a string comparison.

Reviewed By: MaskRay, vitalybuka

Differential Revision: https://reviews.llvm.org/D119515

Added: 
    

Modified: 
    compiler-rt/lib/asan/asan_linux.cpp

Removed: 
    


################################################################################
diff  --git a/compiler-rt/lib/asan/asan_linux.cpp b/compiler-rt/lib/asan/asan_linux.cpp
index 1d92c530bd11..42de45b63271 100644
--- a/compiler-rt/lib/asan/asan_linux.cpp
+++ b/compiler-rt/lib/asan/asan_linux.cpp
@@ -131,30 +131,21 @@ static int FindFirstDSOCallback(struct dl_phdr_info *info, size_t size,
   VReport(2, "info->dlpi_name = %s\tinfo->dlpi_addr = %p\n", info->dlpi_name,
           (void *)info->dlpi_addr);
 
-  // Continue until the first dynamic library is found
-  if (!info->dlpi_name || info->dlpi_name[0] == 0)
-    return 0;
-
-  // Ignore vDSO
-  if (internal_strncmp(info->dlpi_name, "linux-", sizeof("linux-") - 1) == 0)
-    return 0;
+  const char **name = (const char **)data;
 
-#if SANITIZER_FREEBSD || SANITIZER_NETBSD
   // Ignore first entry (the main program)
-  char **p = (char **)data;
-  if (!(*p)) {
-    *p = (char *)-1;
+  if (!*name) {
+    *name = "";
     return 0;
   }
-#endif
 
-#if SANITIZER_SOLARIS
-  // Ignore executable on Solaris
-  if (info->dlpi_addr == 0)
+#    if SANITIZER_LINUX
+  // Ignore vDSO
+  if (internal_strncmp(info->dlpi_name, "linux-", sizeof("linux-") - 1) == 0)
     return 0;
-#endif
+#    endif
 
-  *(const char **)data = info->dlpi_name;
+  *name = info->dlpi_name;
   return 1;
 }
 
@@ -175,7 +166,7 @@ void AsanCheckDynamicRTPrereqs() {
   // Ensure that dynamic RT is the first DSO in the list
   const char *first_dso_name = nullptr;
   dl_iterate_phdr(FindFirstDSOCallback, &first_dso_name);
-  if (first_dso_name && !IsDynamicRTName(first_dso_name)) {
+  if (first_dso_name && first_dso_name[0] && !IsDynamicRTName(first_dso_name)) {
     Report("ASan runtime does not come first in initial library list; "
            "you should either link runtime to your application or "
            "manually preload it with LD_PRELOAD.\n");