libdwelf: Add dwelf_elf_gnu_build_id.

Move internal function __libdwfl_find_build_id to libdwelf and use it to add a public dwelf_elf_gnu_build_id function to extract the NT_GNU_BUILD_ID from an ELF file using either the shdrs or phdrs. Adjust internal callers and add a testcase. Signed-off-by: Mark Wielaard <mjw@redhat.com>
2026-07-01 06:41:51 -04:00 · 2014-04-30 23:00:40 +02:00
parent 920f03dcd3
commit d81d32d2a4
16 changed files with 333 additions and 126 deletions
@@ -1,3 +1,12 @@
+2014-04-30  Mark Wielaard  <mjw@redhat.com>
+
+	* Makefile.am (AM_CPPFLAGS): Add libdwfl and libebl include dirs.
+	(libdwelf_a_SOURCES): Add dwelf_elf_gnu_build_id.c
+	* dwelf_elf_gnu_build_id.c: New file. Moved libdwfl function
+	__libdwfl_find_elf_build_id here.
+	* libdwelf.h (dwelf_elf_gnu_build_id): Declare new function.
+	* libdwelfP.h (dwelf_elf_gnu_build_id): Add internal declaration.
+
 2014-04-24  Florian Weimer  <fweimer@redhat.com>

 	* dwelf_dwarf_gnu_debugaltlink.c: New file.
@@ -30,7 +30,8 @@
 ## not, see <http://www.gnu.org/licenses/>.
 ##
 include $(top_srcdir)/config/eu.am
-AM_CPPFLAGS += -I$(srcdir)/../libelf -I$(srcdir)/../libdw
+AM_CPPFLAGS += -I$(srcdir)/../libelf -I$(srcdir)/../libdw \
+	       -I$(srcdir)/../libdwfl -I$(srcdir)/../libebl
 VERSION = 1

 noinst_LIBRARIES = libdwelf.a libdwelf_pic.a
@@ -38,7 +39,8 @@ noinst_LIBRARIES = libdwelf.a libdwelf_pic.a
 pkginclude_HEADERS = libdwelf.h
 noinst_HEADERS = libdwelfP.h

-libdwelf_a_SOURCES = dwelf_elf_gnu_debuglink.c dwelf_dwarf_gnu_debugaltlink.c
+libdwelf_a_SOURCES = dwelf_elf_gnu_debuglink.c dwelf_dwarf_gnu_debugaltlink.c \
+	dwelf_elf_gnu_build_id.c

 libdwelf = $(libdw)

@@ -0,0 +1,147 @@
+/* Returns the build id if found in a NT_GNU_BUILD_ID note.
+   Copyright (C) 2014 Red Hat, Inc.
+   This file is part of elfutils.
+
+   This file is free software; you can redistribute it and/or modify
+   it under the terms of either
+
+     * the GNU Lesser General Public License as published by the Free
+       Software Foundation; either version 3 of the License, or (at
+       your option) any later version
+
+   or
+
+     * the GNU General Public License as published by the Free
+       Software Foundation; either version 2 of the License, or (at
+       your option) any later version
+
+   or both in parallel, as here.
+
+   elfutils is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+   You should have received copies of the GNU General Public License and
+   the GNU Lesser General Public License along with this program.  If
+   not, see <http://www.gnu.org/licenses/>.  */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include "libdwelfP.h"
+#include "libdwflP.h"
+
+#define NO_VADDR	((GElf_Addr) -1l)
+
+/* Defined here for reuse. The dwelf interface doesn't care about the
+   address of the note, but libdwfl does.  */
+static int
+find_elf_build_id (Dwfl_Module *mod, int e_type, Elf *elf,
+		   const void **build_id_bits, GElf_Addr *build_id_elfaddr,
+		   int *build_id_len)
+{
+  int check_notes (Elf_Data *data, GElf_Addr data_elfaddr)
+  {
+    size_t pos = 0;
+    GElf_Nhdr nhdr;
+    size_t name_pos;
+    size_t desc_pos;
+    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"))
+	{
+	  *build_id_bits = data->d_buf + desc_pos;
+	  *build_id_elfaddr = (data_elfaddr == NO_VADDR
+			       ? 0 : data_elfaddr + desc_pos);
+	  *build_id_len = nhdr.n_descsz;
+	  return 1;
+	}
+    return 0;
+  }
+
+  size_t shstrndx = SHN_UNDEF;
+  int result = 0;
+
+  Elf_Scn *scn = elf_nextscn (elf, NULL);
+
+  if (scn == NULL)
+    {
+      /* No sections, have to look for phdrs.  */
+      size_t phnum;
+      if (unlikely (elf_getphdrnum (elf, &phnum) != 0))
+	{
+	  if (mod != NULL)
+	    __libdwfl_seterrno (DWFL_E_LIBELF);
+	  return -1;
+	}
+      for (size_t i = 0; result == 0 && i < phnum; ++i)
+	{
+	  GElf_Phdr phdr_mem;
+	  GElf_Phdr *phdr = gelf_getphdr (elf, i, &phdr_mem);
+	  if (likely (phdr != NULL) && phdr->p_type == PT_NOTE)
+	    result = check_notes (elf_getdata_rawchunk (elf,
+							phdr->p_offset,
+							phdr->p_filesz,
+							ELF_T_NHDR),
+				  phdr->p_vaddr);
+	}
+    }
+  else
+    do
+      {
+	GElf_Shdr shdr_mem;
+	GElf_Shdr *shdr = gelf_getshdr (scn, &shdr_mem);
+	if (likely (shdr != NULL) && shdr->sh_type == SHT_NOTE)
+	  {
+	    /* Determine the right sh_addr in this module.  */
+	    GElf_Addr vaddr = 0;
+	    if (!(shdr->sh_flags & SHF_ALLOC))
+	      vaddr = NO_VADDR;
+	    else if (mod == NULL || e_type != ET_REL)
+	      vaddr = shdr->sh_addr;
+	    else if (__libdwfl_relocate_value (mod, elf, &shstrndx,
+					       elf_ndxscn (scn), &vaddr))
+	      vaddr = NO_VADDR;
+	    result = check_notes (elf_getdata (scn, NULL), vaddr);
+	  }
+      }
+    while (result == 0 && (scn = elf_nextscn (elf, scn)) != NULL);
+
+  return result;
+}
+
+int
+internal_function
+__libdwfl_find_elf_build_id (Dwfl_Module *mod, Elf *elf,
+			     const void **build_id_bits,
+			     GElf_Addr *build_id_elfaddr, int *build_id_len)
+{
+  GElf_Ehdr ehdr_mem, *ehdr = gelf_getehdr (elf, &ehdr_mem);
+  if (unlikely (ehdr == NULL))
+    {
+      __libdwfl_seterrno (DWFL_E_LIBELF);
+      return -1;
+    }
+  // MOD->E_TYPE is zero here.
+  assert (ehdr->e_type != ET_REL || mod != NULL);
+
+  return find_elf_build_id (mod, ehdr->e_type, elf,
+			    build_id_bits, build_id_elfaddr, build_id_len);
+}
+
+ssize_t
+dwelf_elf_gnu_build_id (Elf *elf, const void **build_idp)
+{
+  GElf_Addr build_id_elfaddr;
+  int build_id_len;
+  int result = find_elf_build_id (NULL, ET_NONE, elf, build_idp,
+				  &build_id_elfaddr, &build_id_len);
+  if (result > 0)
+    return build_id_len;
+
+  return result;
+}
+INTDEF(dwelf_elf_gnu_build_id)
@@ -57,6 +57,14 @@ extern ssize_t dwelf_dwarf_gnu_debugaltlink (Dwarf *dwarf,
 					     const char **namep,
 					     const void **build_idp);

+/* Returns the build ID as found in a NT_GNU_BUILD_ID note from either
+   a SHT_NOTE section or from a PT_NOTE segment if the ELF file
+   doesn't contain any section headers.  On success a pointer to the
+   build ID is written to *BUILDID_P, and the positive length of the
+   build ID is returned.  Returns 0 if the ELF lacks a NT_GNU_BUILD_ID
+   note.  Returns -1 in case of malformed data or other errors.  */
+extern ssize_t dwelf_elf_gnu_build_id (Elf *elf, const void **build_idp);
+
 #ifdef __cplusplus
 }
 #endif
@@ -37,5 +37,6 @@
 /* Avoid PLT entries.  */
 INTDECL (dwelf_elf_gnu_debuglink)
 INTDECL (dwelf_dwarf_gnu_debugaltlink)
+INTDECL (dwelf_elf_gnu_build_id)

 #endif	/* libdwelfP.h */