elfutils/elfutils-0.154-dwz.patch

https://lists.fedorahosted.org/pipermail/elfutils-devel/2012-July/002418.html

From b1e42797293bcf34385d5cb0a18e8c773279241b Mon Sep 17 00:00:00 2001
From: Mark Wielaard <mjw@redhat.com>
Date: Fri, 22 Jun 2012 12:02:45 +0200
Subject: [PATCH] libdw: Add support for DWZ multifile forms
 DW_FORM_GNU_ref_alt/strp_alt.

DWZ multifile forms http://www.dwarfstd.org/ShowIssue.php?issue=120604.1
DW_FORM_GNU_ref_alt and DW_FORM_GNU_strp_alt reference an alternative
debuginfo file.  dwarf_begin and dwarf_begin_elf will try to use this
automatically.  There are no user visible changes to the libdw interface.

dwarf_formref_die, dwarf_formstring and dwarf_formudata can now return
a Dwarf_Die which comes from a CU in the alternative Dwarf descriptor.

__libdw_read_offset was adjusted to take an alternative Dwarf descriptor
into account.

Signed-off-by: Mark Wielaard <mjw@redhat.com>

diff --git a/libdw/dwarf.h b/libdw/dwarf.h
index f41d296..81bc7fe 100644
--- a/libdw/dwarf.h
+++ b/libdw/dwarf.h
@@ -299,7 +299,10 @@ enum
     DW_FORM_sec_offset = 0x17,
     DW_FORM_exprloc = 0x18,
     DW_FORM_flag_present = 0x19,
-    DW_FORM_ref_sig8 = 0x20
+    DW_FORM_ref_sig8 = 0x20,
+
+    DW_FORM_GNU_ref_alt = 0x1f20, /* offset in alternate .debuginfo.  */
+    DW_FORM_GNU_strp_alt = 0x1f21 /* offset in alternate .debug_str. */
   };
 
 
diff --git a/libdw/dwarf_begin.c b/libdw/dwarf_begin.c
index 1f3fc3b..9f3050f 100644
--- a/libdw/dwarf_begin.c
+++ b/libdw/dwarf_begin.c
@@ -98,3 +98,4 @@ dwarf_begin (fd, cmd)
 
   return result;
 }
+INTDEF(dwarf_begin)
diff --git a/libdw/dwarf_begin_elf.c b/libdw/dwarf_begin_elf.c
index 3e01800..fd95770 100644
--- a/libdw/dwarf_begin_elf.c
+++ b/libdw/dwarf_begin_elf.c
@@ -31,12 +31,17 @@
 # include <config.h>
 #endif
 
+#include <assert.h>
+#include <inttypes.h>
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdlib.h>
+#include <stdio.h>
 #include <string.h>
 #include <unistd.h>
+#include <sys/types.h>
 #include <sys/stat.h>
+#include <fcntl.h>
 
 #include "libdwP.h"
 
@@ -66,6 +71,110 @@ static const char dwarf_scnnames[IDX_last][17] =
 };
 #define ndwarf_scnnames (sizeof (dwarf_scnnames) / sizeof (dwarf_scnnames[0]))
 
+internal_function int
+__check_build_id (Dwarf *dw, const uint8_t *build_id, const size_t id_len)
+{
+  if (dw == NULL)
+    return -1;
+
+  Elf *elf = dw->elf;
+  Elf_Scn *scn = elf_nextscn (elf, NULL);
+  if (scn == NULL)
+    return -1;
+
+  do
+    {
+      GElf_Shdr shdr_mem;
+      GElf_Shdr *shdr = gelf_getshdr (scn, &shdr_mem);
+      if (likely (shdr != NULL) && shdr->sh_type == SHT_NOTE)
+	{
+	  size_t pos = 0;
+	  GElf_Nhdr nhdr;
+	  size_t name_pos;
+	  size_t desc_pos;
+	  Elf_Data *data = elf_getdata (scn, NULL);
+	  while ((pos = gelf_getnote (data, pos, &nhdr, &name_pos,
+				      &desc_pos)) > 0)
+	    if (nhdr.n_type == NT_GNU_BUILD_ID
+	        && nhdr.n_namesz == sizeof "GNU"
+		&& ! memcmp (data->d_buf + name_pos, "GNU", sizeof "GNU"))
+	      return (nhdr.n_descsz == id_len
+		      && ! memcmp (data->d_buf + desc_pos,
+				   build_id, id_len)) ? 0 : 1;
+        }
+      }
+    while ((scn = elf_nextscn (elf, scn)) != NULL);
+
+  return -1;
+}
+
+/* Try to open an debug alt link by name, checking build_id.
+   Marks free_alt on success, return NULL on failure.  */
+static Dwarf *
+try_debugaltlink (Dwarf *result, const char *try_name,
+		   const uint8_t *build_id, const size_t id_len)
+{
+  int fd = open (try_name, O_RDONLY);
+  if (fd > 0)
+    {
+      result->alt_dwarf = INTUSE (dwarf_begin) (fd, DWARF_C_READ);
+      if (result->alt_dwarf != NULL)
+	{
+	  Elf *elf = result->alt_dwarf->elf;
+	  if (__check_build_id (result->alt_dwarf, build_id, id_len) == 0
+	      && elf_cntl (elf, ELF_C_FDREAD) == 0)
+	    {
+	      close (fd);
+	      result->free_alt = 1;
+	      return result;
+	    }
+	  INTUSE (dwarf_end) (result->alt_dwarf);
+	}
+      close (fd);
+    }
+  return NULL;
+}
+
+/* For dwz multifile support, ignore if it looks wrong.  */
+static Dwarf *
+open_debugaltlink (Dwarf *result, const char *alt_name,
+		   const uint8_t *build_id, const size_t id_len)
+{
+  /* First try the name itself, it is either an absolute path or
+     a relative one.  Sadly we don't know relative from where at
+     this point.  */
+  if (try_debugaltlink (result, alt_name, build_id, id_len) != NULL)
+    return result;
+
+  /* Lets try based on the build-id.  This is somewhat distro specific,
+     we are following the Fedora implementation described at
+  https://fedoraproject.org/wiki/Releases/FeatureBuildId#Find_files_by_build_ID
+   */
+#define DEBUG_PREFIX "/usr/lib/debug/.build-id/"
+#define PREFIX_LEN sizeof (DEBUG_PREFIX)
+  char id_name[PREFIX_LEN + 1 + id_len * 2 + sizeof ".debug" - 1];
+  strcpy (id_name, DEBUG_PREFIX);
+  int n = snprintf (&id_name[PREFIX_LEN  - 1],
+		    4, "%02" PRIx8 "/", (uint8_t) build_id[0]);
+  assert (n == 3);
+  for (size_t i = 1; i < id_len; ++i)
+    {
+      n = snprintf (&id_name[PREFIX_LEN - 1 + 3 + (i - 1) * 2],
+		    3, "%02" PRIx8, (uint8_t) build_id[i]);
+      assert (n == 2);
+    }
+  strcpy (&id_name[PREFIX_LEN - 1 + 3 + (id_len - 1) * 2],
+	  ".debug");
+
+  if (try_debugaltlink (result, id_name, build_id, id_len))
+    return result;
+
+  /* Everything failed, mark this Dwarf as not having an alternate,
+     but don't fail the load.  The user may want to set it by hand
+     before usage.  */
+  result->alt_dwarf = NULL;
+  return result;
+}
 
 static Dwarf *
 check_section (Dwarf *result, GElf_Ehdr *ehdr, Elf_Scn *scn, bool inscngrp)
@@ -110,6 +219,20 @@ check_section (Dwarf *result, GElf_Ehdr *ehdr, Elf_Scn *scn, bool inscngrp)
       return NULL;
     }
 
+  /* For dwz multifile support, ignore if it looks wrong.  */
+  if (strcmp (scnname, ".gnu_debugaltlink") == 0)
+    {
+      Elf_Data *data = elf_getdata (scn, NULL);
+      if (data != NULL && data->d_size != 0)
+	{
+	  const char *alt_name = data->d_buf;
+	  const void *build_id = memchr (data->d_buf, '\0', data->d_size);
+	  const int id_len = data->d_size - (build_id - data->d_buf + 1);
+	  if (alt_name && build_id && id_len > 0)
+	    return open_debugaltlink (result, alt_name, build_id + 1, id_len);
+	}
+    }
+
 
   /* Recognize the various sections.  Most names start with .debug_.  */
   size_t cnt;
diff --git a/libdw/dwarf_end.c b/libdw/dwarf_end.c
index b77988f..e65314a 100644
--- a/libdw/dwarf_end.c
+++ b/libdw/dwarf_end.c
@@ -111,6 +111,10 @@ dwarf_end (dwarf)
       if (dwarf->free_elf)
 	elf_end (dwarf->elf);
 
+      /* Free the alternative Dwarf descriptor if necessary.  */
+      if (dwarf->free_alt)
+	INTUSE (dwarf_end) (dwarf->alt_dwarf);
+
       /* Free the context descriptor.  */
       free (dwarf);
     }
diff --git a/libdw/dwarf_error.c b/libdw/dwarf_error.c
index 89047dc..2292914 100644
--- a/libdw/dwarf_error.c
+++ b/libdw/dwarf_error.c
@@ -91,6 +91,7 @@ static const char *errmsgs[] =
     [DWARF_E_INVALID_OFFSET] = N_("invalid offset"),
     [DWARF_E_NO_DEBUG_RANGES] = N_(".debug_ranges section missing"),
     [DWARF_E_INVALID_CFI] = N_("invalid CFI section"),
+    [DWARF_E_NO_ALT_DEBUGLINK] = N_("no alternative debug link found"),
   };
 #define nerrmsgs (sizeof (errmsgs) / sizeof (errmsgs[0]))
 
diff --git a/libdw/dwarf_formref.c b/libdw/dwarf_formref.c
index a2554e9..86da7ea 100644
--- a/libdw/dwarf_formref.c
+++ b/libdw/dwarf_formref.c
@@ -72,6 +72,8 @@ __libdw_formref (attr, return_offset)
 
     case DW_FORM_ref_addr:
     case DW_FORM_ref_sig8:
+    case DW_FORM_GNU_ref_alt:
+      /* These aren't handled by dwarf_formref, only by dwarf_formref_die.  */
       __libdw_seterrno (DWARF_E_INVALID_REFERENCE);
       return -1;
 
diff --git a/libdw/dwarf_formref_die.c b/libdw/dwarf_formref_die.c
index 342f6b9..f070127 100644
--- a/libdw/dwarf_formref_die.c
+++ b/libdw/dwarf_formref_die.c
@@ -46,7 +46,7 @@ dwarf_formref_die (attr, result)
   struct Dwarf_CU *cu = attr->cu;
 
   Dwarf_Off offset;
-  if (attr->form == DW_FORM_ref_addr)
+  if (attr->form == DW_FORM_ref_addr || attr->form == DW_FORM_GNU_ref_alt)
     {
       /* This has an absolute offset.  */
 
@@ -54,11 +54,20 @@ dwarf_formref_die (attr, result)
 			  ? cu->address_size
 			  : cu->offset_size);
 
-      if (__libdw_read_offset (cu->dbg, IDX_debug_info, attr->valp,
+      Dwarf *dbg_ret = (attr->form == DW_FORM_GNU_ref_alt
+			? cu->dbg->alt_dwarf : cu->dbg);
+
+      if (dbg_ret == NULL)
+	{
+	  __libdw_seterrno (DWARF_E_NO_ALT_DEBUGLINK);
+	  return NULL;
+	}
+
+      if (__libdw_read_offset (cu->dbg, dbg_ret, IDX_debug_info, attr->valp,
 			       ref_size, &offset, IDX_debug_info, 0))
 	return NULL;
 
-      return INTUSE(dwarf_offdie) (cu->dbg, offset, result);
+      return INTUSE(dwarf_offdie) (dbg_ret, offset, result);
     }
 
   Elf_Data *data;
diff --git a/libdw/dwarf_formstring.c b/libdw/dwarf_formstring.c
index fe2183a..c66454e 100644
--- a/libdw/dwarf_formstring.c
+++ b/libdw/dwarf_formstring.c
@@ -49,8 +49,17 @@ dwarf_formstring (attrp)
     return (const char *) attrp->valp;
 
   Dwarf *dbg = attrp->cu->dbg;
+  Dwarf *dbg_ret = attrp->form == DW_FORM_GNU_strp_alt ? dbg->alt_dwarf : dbg;
 
-  if (unlikely (attrp->form != DW_FORM_strp)
+  if (unlikely (dbg_ret == NULL))
+    {
+      __libdw_seterrno (DWARF_E_NO_ALT_DEBUGLINK);
+      return NULL;
+    }
+
+
+  if (unlikely (attrp->form != DW_FORM_strp
+		   && attrp->form != DW_FORM_GNU_strp_alt)
       || dbg->sectiondata[IDX_debug_str] == NULL)
     {
       __libdw_seterrno (DWARF_E_NO_STRING);
@@ -58,10 +67,10 @@ dwarf_formstring (attrp)
     }
 
   uint64_t off;
-  if (__libdw_read_offset (dbg, cu_sec_idx (attrp->cu), attrp->valp,
+  if (__libdw_read_offset (dbg, dbg_ret, cu_sec_idx (attrp->cu), attrp->valp,
 			   attrp->cu->offset_size, &off, IDX_debug_str, 1))
     return NULL;
 
-  return (const char *) dbg->sectiondata[IDX_debug_str]->d_buf + off;
+  return (const char *) dbg_ret->sectiondata[IDX_debug_str]->d_buf + off;
 }
 INTDEF(dwarf_formstring)
diff --git a/libdw/dwarf_formudata.c b/libdw/dwarf_formudata.c
index f08e0d8..41b09e1 100644
--- a/libdw/dwarf_formudata.c
+++ b/libdw/dwarf_formudata.c
@@ -52,7 +52,8 @@ __libdw_formptr (Dwarf_Attribute *attr, int sec_index,
   Dwarf_Word offset;
   if (attr->form == DW_FORM_sec_offset)
     {
-      if (__libdw_read_offset (attr->cu->dbg, cu_sec_idx (attr->cu), attr->valp,
+      if (__libdw_read_offset (attr->cu->dbg, attr->cu->dbg,
+			       cu_sec_idx (attr->cu), attr->valp,
 			       attr->cu->offset_size, &offset, sec_index, 0))
 	return NULL;
     }
@@ -63,7 +64,8 @@ __libdw_formptr (Dwarf_Attribute *attr, int sec_index,
       {
       case DW_FORM_data4:
       case DW_FORM_data8:
-	if (__libdw_read_offset (attr->cu->dbg, cu_sec_idx (attr->cu),
+	if (__libdw_read_offset (attr->cu->dbg, attr->cu->dbg,
+				 cu_sec_idx (attr->cu),
 				 attr->valp,
 				 attr->form == DW_FORM_data4 ? 4 : 8,
 				 &offset, sec_index, 0))
diff --git a/libdw/dwarf_getpubnames.c b/libdw/dwarf_getpubnames.c
index 4ea3889..12728a3 100644
--- a/libdw/dwarf_getpubnames.c
+++ b/libdw/dwarf_getpubnames.c
@@ -102,7 +102,8 @@ get_offsets (Dwarf *dbg)
 	}
 
       /* Get the CU offset.  */
-      if (__libdw_read_offset (dbg, IDX_debug_pubnames, readp + 2, len_bytes,
+      if (__libdw_read_offset (dbg, dbg, IDX_debug_pubnames,
+			       readp + 2, len_bytes,
 			       &mem[cnt].cu_offset, IDX_debug_info, 3))
 	/* Error has been already set in reader.  */
 	goto err_return;
diff --git a/libdw/libdwP.h b/libdw/libdwP.h
index 77e1b31..da82e5d 100644
--- a/libdw/libdwP.h
+++ b/libdw/libdwP.h
@@ -116,6 +116,7 @@ enum
   DWARF_E_INVALID_OFFSET,
   DWARF_E_NO_DEBUG_RANGES,
   DWARF_E_INVALID_CFI,
+  DWARF_E_NO_ALT_DEBUGLINK
 };
 
 
@@ -127,6 +128,9 @@ struct Dwarf
   /* The underlying ELF file.  */
   Elf *elf;
 
+  /* dwz alternate DWARF file.  */
+  Dwarf *alt_dwarf;
+
   /* The section data.  */
   Elf_Data *sectiondata[IDX_last];
 
@@ -141,6 +145,9 @@ struct Dwarf
   /* If true, we allocated the ELF descriptor ourselves.  */
   bool free_elf;
 
+  /* If true, we allocated the Dwarf descriptor for alt_dwarf ourselves.  */
+  bool free_alt;
+
   /* Information for traversing the .debug_pubnames section.  This is
      an array and separately allocated with malloc.  */
   struct pubnames_s
@@ -580,13 +587,13 @@ __libdw_read_offset_inc (Dwarf *dbg,
 }
 
 static inline int
-__libdw_read_offset (Dwarf *dbg,
+__libdw_read_offset (Dwarf *dbg, Dwarf *dbg_ret,
 		     int sec_index, const unsigned char *addr,
 		     int width, Dwarf_Off *ret, int sec_ret,
 		     size_t size)
 {
   READ_AND_RELOCATE (__libdw_relocate_offset, (*ret));
-  return __libdw_offset_in_section (dbg, sec_ret, *ret, size);
+  return __libdw_offset_in_section (dbg_ret, sec_ret, *ret, size);
 }
 
 static inline size_t
@@ -617,12 +624,19 @@ unsigned char * __libdw_formptr (Dwarf_Attribute *attr, int sec_index,
 				 Dwarf_Off *offsetp)
   internal_function;
 
+/* Checks that the build_id of the underlying Elf matches the expected.
+   Returns zero on match, -1 on error or no build_id found or 1 when
+   build_id doesn't match.  */
+int __check_build_id (Dwarf *dw, const uint8_t *build_id, const size_t id_len)
+  internal_function;
+
 
 
 /* Aliases to avoid PLTs.  */
 INTDECL (dwarf_aggregate_size)
 INTDECL (dwarf_attr)
 INTDECL (dwarf_attr_integrate)
+INTDECL (dwarf_begin)
 INTDECL (dwarf_begin_elf)
 INTDECL (dwarf_child)
 INTDECL (dwarf_dieoffset)
diff --git a/libdw/libdw_form.c b/libdw/libdw_form.c
index 2ff8868..c476a6e 100644
--- a/libdw/libdw_form.c
+++ b/libdw/libdw_form.c
@@ -58,6 +58,8 @@ __libdw_form_val_len (Dwarf *dbg, struct Dwarf_CU *cu, unsigned int form,
 
     case DW_FORM_strp:
     case DW_FORM_sec_offset:
+    case DW_FORM_GNU_ref_alt:
+    case DW_FORM_GNU_strp_alt:
       result = cu->offset_size;
       break;
 
diff --git a/src/readelf.c b/src/readelf.c
index 3a27f8f..644e0f7 100644
--- a/src/readelf.c
+++ b/src/readelf.c
@@ -3651,6 +3651,20 @@ dwarf_form_string (unsigned int form)
 
   if (likely (form < nknown_forms))
     result = known_forms[form];
+  else
+    {
+      /* GNU extensions use vendor numbers.  */
+      switch (form)
+	{
+	case DW_FORM_GNU_ref_alt:
+	  result = "GNU_ref_alt";
+	  break;
+
+	case DW_FORM_GNU_strp_alt:
+	  result = "GNU_strp_alt";
+	  break;
+	}
+    }
 
   if (unlikely (result == NULL))
     {
@@ -5593,6 +5607,7 @@ attr_callback (Dwarf_Attribute *attrp, void *arg)
     case DW_FORM_indirect:
     case DW_FORM_strp:
     case DW_FORM_string:
+    case DW_FORM_GNU_strp_alt:
       if (cbargs->silent)
 	break;
       const char *str = dwarf_formstring (attrp);
@@ -5608,7 +5623,8 @@ attr_callback (Dwarf_Attribute *attrp, void *arg)
     case DW_FORM_ref8:
     case DW_FORM_ref4:
     case DW_FORM_ref2:
-    case DW_FORM_ref1:;
+    case DW_FORM_ref1:
+    case DW_FORM_GNU_ref_alt:
       if (cbargs->silent)
 	break;
       Dwarf_Die ref;