Ignore kernel functions with "absolute" addresses.

translate.cxx (dump_unwindsyms): Augment the test for creating the
stap-symbols to be STT_FUNC && !(SHN_UNDEF || SHN_ABS). The combination
STT_FUNC && SHN_ABS only seems to occur on older i386 kernels and covers
the vDSO "functions" we were seeing.

1 files changed, 6 insertions, 7 deletions

diff --git a/translate.cxx b/translate.cxx
index e87e9876..c0e76a02 100644
--- a/translate.cxx
+++ b/translate.cxx
@@ -4538,18 +4538,17 @@ dump_unwindsyms (Dwfl_Module *m,
                 clog << "Found kernel _stext 0x" << hex << extra_offset << dec << endl;
             }
 
+          // We only need the function symbols to identify kernel-mode
+          // PC's, so we omit undefined or "fake" absolute addresses.
+          // These fake absolute addresses occur in some older i386
+          // kernels to indicate they are vDSO symbols, not real
+          // functions in the kernel.
           if (GELF_ST_TYPE (sym.st_info) == STT_FUNC &&
-              sym.st_shndx != SHN_UNDEF)
+              ! (sym.st_shndx == SHN_UNDEF || sym.st_shndx == SHN_ABS))
             {
               Dwarf_Addr sym_addr = sym.st_value;
               const char *secname = NULL;
 
-              // Symbol addresses before the base address of the module
-              // are suspect. Older kernels had those for some vsdo
-              // symbols. They mess up our logic, ignore them.
-              if (sym_addr < base)
-                continue;
-
               if (n > 0) // only try to relocate if there exist relocation bases
                 {
                   int ki = dwfl_module_relocate_address (m, &sym_addr);