[PATCH 1/3] PR4886: Extract build-id from debuginfo file.

[Wenji Huang <wenji dot huang at oracle dot com>]

Hi,

Update the previous patch for checking build-id. It will cover kernel 
and external module. For non-build-id case, it will run as normal. Only 
does work in case of LD >=2.18 and kernel >=2.6.23.

The patch will provide sanity checking through validating debuginfo 
based-on build-id. The build-id information will be stored into _stp_module.
---
 runtime/sym.h |   10 ++++++++++
 translate.cxx |   39 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+), 0 deletions(-)

diff --git a/runtime/sym.h b/runtime/sym.h
index 5888d2c..f8034d6 100644
--- a/runtime/sym.h
+++ b/runtime/sym.h
@@ -45,6 +45,16 @@ struct _stp_module {
        uint32_t unwind_data_len;
        uint32_t unwind_hdr_len;
        uint32_t unwind_is_ehframe; /* unwind data comes from .eh_frame */
+       /* build-id information */
+       unsigned char *build_id_bits;
+       unsigned long  build_id_offset;
+       unsigned long  notes_sect; /* kernel: 1 - no build-id
+                                             2 - has build-id
+                                     module: 0 - unloaded
+                                             1 - loaded and no build-id
+                                             Other - note address
+                                  */
+       int build_id_len;
 };


diff --git a/translate.cxx b/translate.cxx
index e92c848..a9695f1 100644
--- a/translate.cxx
+++ b/translate.cxx
@@ -4413,6 +4413,23 @@ dump_unwindsyms (Dwfl_Module *m,
   int syments = dwfl_module_getsymtab(m);
   assert(syments);

+  //extract build-id from debuginfo file
+  int build_id_len = 0;
+  unsigned char *build_id_bits;
+  GElf_Addr build_id_vaddr;
+
+  if ((build_id_len=dwfl_module_build_id(m,
+                                        (const unsigned char 
**)&build_id_bits,
+                                         &build_id_vaddr)) > 0)
+  {
+        if (c->session.verbose > 1) {
+           clog << "Found build-id in " << name
+                << ", length " << build_id_len;
+           clog << ", end at 0x" << hex << build_id_vaddr
+                << dec << endl;
+        }
+  }
+
   // Look up the relocation basis for symbols
   int n = dwfl_module_relocations (m);

@@ -4581,6 +4598,28 @@ dump_unwindsyms (Dwfl_Module *m,
   c->output << ".num_sections = sizeof(_stp_module_" << stpmod_idx << 
"_sections)/"
             << "sizeof(struct _stp_section), " << endl;

+  if (build_id_len > 0) {
+        c->output << ".build_id_bits = \"" ;
+        for (int j=0; j<build_id_len;j++)
+                c->output << "\\x" << hex
+                          << (unsigned short) *(build_id_bits+j) << dec;
+
+       c->output << "\", " << endl;
+       c->output << ".build_id_len = " << build_id_len << ", " << endl;
+
+       if (modname == "kernel")
+                c->output << ".build_id_offset = 0x" << hex << 
build_id_vaddr
+                         << dec << ", " << endl;
+       else
+                c->output << ".build_id_offset = 0x" << hex
+                         << build_id_vaddr - base
+                         << dec << ", " << endl;
+  } else
+        c->output << ".build_id_len = 0, " << endl;
+
+  //initialize the note section representing unloaded
+  c->output << ".notes_sect = 0," << endl;
+
   c->output << "};" << endl << endl;

   c->undone_unwindsym_modules.erase (modname);
--
1.5.6