From f3521f1d69312eb476c53eea06ee1187844efe18 Mon Sep 17 00:00:00 2001

From: Mark Wielaard <mark@klomp.org>

Date: Sat, 9 Dec 2017 23:01:29 +0100

Subject: [PATCH] Fix gnu debug alt file resolving.

The path to the alt file is relative to the actual debug file.

Make sure that we got the real file, not a (build-id) symlink.

---

 coregrind/m_debuginfo/readelf.c | 57 +++++++++++++++++++++++++++++++++++++++--

 1 file changed, 55 insertions(+), 2 deletions(-)

diff --git a/coregrind/m_debuginfo/readelf.c b/coregrind/m_debuginfo/readelf.c

index e612250..2d52322 100644

--- a/coregrind/m_debuginfo/readelf.c

+++ b/coregrind/m_debuginfo/readelf.c

@@ -33,6 +33,7 @@

 #include "pub_core_basics.h"

 #include "pub_core_vki.h"

+#include "pub_core_vkiscnums.h"

 #include "pub_core_debuginfo.h"

 #include "pub_core_libcbase.h"

 #include "pub_core_libcprint.h"

@@ -40,6 +41,7 @@

 #include "pub_core_machine.h"      /* VG_ELF_CLASS */

 #include "pub_core_options.h"

 #include "pub_core_oset.h"

+#include "pub_core_syscall.h"

 #include "pub_core_tooliface.h"    /* VG_(needs) */

 #include "pub_core_xarray.h"

 #include "priv_misc.h"             /* dinfo_zalloc/free/strdup */

@@ -1527,6 +1529,51 @@ static Bool check_compression(ElfXX_Shdr* h, DiSlice* s) {

     return True;

 }

+/* Helper function to get the readlink path. Returns NULL on error.

+   Otherwise the result needs to be released with dinfo_free.

+*/

+static HChar* readlink_path (const HChar *path)

+{

+   SizeT bufsiz = VG_(strlen)(path);

+   HChar *buf = ML_(dinfo_strdup)("readlink_path.strdup", path);

+   UInt   tries = 8;

+

+   while (tries > 0) {

+      SysRes res;

+#if defined(VGP_arm64_linux)

+      res = VG_(do_syscall4)(__NR_readlinkat, VKI_AT_FDCWD,

+                                              (UWord)path, (UWord)buf, bufsiz);

+#elif defined(VGO_linux) || defined(VGO_darwin)

+      res = VG_(do_syscall3)(__NR_readlink, (UWord)path, (UWord)buf, bufsiz);

+#elif defined(VGO_solaris)

+      res = VG_(do_syscall4)(__NR_readlinkat, VKI_AT_FDCWD, (UWord)path,

+                             (UWord)buf, bufsiz);

+#else

+#       error Unknown OS

+#endif

+   if (sr_isError(res))

+      return NULL;

+

+   SSizeT r = sr_Res(res);

+   if (r < 0) break;

+      if (r == bufsiz) {  // buffer too small; increase and retry

+         bufsiz *= 2 + 16;

+         buf = ML_(dinfo_realloc)("readlink_path.realloc", buf, bufsiz);

+         tries--;

+         continue;

+      }

+      buf[r] = '\0';

+      break;

+   }

+

+   if (tries == 0) { // We tried, but weird long path?

+      ML_(dinfo_free)(buf);

+      return NULL;

+   }

+

+  return buf;

+}

+

 /* The central function for reading ELF debug info.  For the

    object/exe specified by the DebugInfo, find ELF sections, then read

    the symbols, line number info, file name info, CFA (stack-unwind

@@ -2926,8 +2973,12 @@ Bool ML_(read_elf_debug_info) ( struct _DebugInfo* di )

                                 (debugaltlink_escn.szB - buildid_offset)

                                 * 2 + 1);

-         /* The altfile might be relative to the debug file or main file. */

+         /* The altfile might be relative to the debug file or main file.

+	    Make sure that we got the real file, not a symlink.  */

          HChar *dbgname = di->fsm.dbgname ? di->fsm.dbgname : di->fsm.filename;

+         HChar* rdbgname = readlink_path (dbgname);

+         if (rdbgname == NULL)

+            rdbgname = ML_(dinfo_strdup)("rdbgname", dbgname);

          for (j = 0; j < debugaltlink_escn.szB - buildid_offset; j++)

             VG_(sprintf)(

@@ -2937,9 +2988,11 @@ Bool ML_(read_elf_debug_info) ( struct _DebugInfo* di )

                                         + buildid_offset + j));

          /* See if we can find a matching debug file */

-         aimg = find_debug_file( di, dbgname, altbuildid,

+         aimg = find_debug_file( di, rdbgname, altbuildid,

                                  altfile_str_m, 0, True );

+         ML_(dinfo_free)(rdbgname);

+

          if (altfile_str_m)

             ML_(dinfo_free)(altfile_str_m);

          ML_(dinfo_free)(altbuildid);

-- 

1.8.3.1