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PATCH] Properly handle note sections and segments

From: "H.J. Lu" <hjl dot tools at gmail dot com>
To: Binutils <binutils at sourceware dot org>
Date: Sat, 25 Nov 2017 09:22:48 -0800
Subject: PATCH] Properly handle note sections and segments
Authentication-results: sourceware.org; auth=none

On Sat, Nov 25, 2017 at 6:17 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Fri, Nov 24, 2017 at 3:49 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> gABI specifies that PT_NOTE alignment should be aligned to 4 bytes
>> for 32-bit objects and to 8 bytes for 64-bit objects.  But on Linux,
>> .note.ABI-tag and .note.gnu.build-id notes are always aligned to 4
>> bytes.  We allow either 4 byte or 8 byte alignments.
>>
>> OK for master?
>>
>> H.J.
>> ---
>>         * readelf.c (process_notes_at): Return FALSE if alignment of
>>         note section isn't 4 nor 8 bytes.
>
> This patch is incorrect.  Here is the updated patch, which also fixes
> incorrect note section alignment:
>
> https://sourceware.org/bugzilla/show_bug.cgi?id=22492
>

This updated patch also fixed:

https://sourceware.org/bugzilla/show_bug.cgi?id=22490

and dumps CORE PT_NOTE segments.

OK for master?


-- 
H.J.

From d199b872fa237a0f173092a8b38d070e689081c2 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Fri, 24 Nov 2017 15:47:10 -0800
Subject: [PATCH] Properly handle note sections and segments

gABI specifies that notes should be aligned to 4 bytes in 32-bit objects
and to 8 bytes in 64-bit objects.  As a Linux extension, we support 4
byte alignment in 64-bit objects.  obj_elf_version and sco_id pad note
section to 4 byte alignment:

frag_align (2, 0, 0);

They should set section alignment to 4 bytes.  When dumping note sections,
if section alignment is less than 4, we treate alignment as 4 bytes to
handle note sections with incorrect section alignment.

readelf should also be able to dump CORE PT_NOTE segment, like

Displaying notes found at file offset 0x00000548 with length 0x00000cbc:
  Owner                 Data size	Description
  CORE                 0x00000150	NT_PRSTATUS (prstatus structure)
  CORE                 0x00000088	NT_PRPSINFO (prpsinfo structure)
  CORE                 0x00000080	NT_SIGINFO (siginfo_t data)
  CORE                 0x00000140	NT_AUXV (auxiliary vector)
  CORE                 0x00000358	NT_FILE (mapped files)
    Page size: 4096
                 Start                 End         Page Offset
    0x0000000000400000  0x0000000000401000  0x0000000000000000
        /export/build/gnu/gdb/build-x86_64-linux/gdb/testsuite/outputs/gdb.base/auxv/auxv
    0x0000000000600000  0x0000000000601000  0x0000000000000000
        /export/build/gnu/gdb/build-x86_64-linux/gdb/testsuite/outputs/gdb.base/auxv/auxv
    0x0000000000601000  0x0000000000602000  0x0000000000000001
        /export/build/gnu/gdb/build-x86_64-linux/gdb/testsuite/outputs/gdb.base/auxv/auxv
    0x00007ffff7659000  0x00007ffff7834000  0x0000000000000000
        /usr/lib64/libc-2.26.so
    0x00007ffff7834000  0x00007ffff7a33000  0x00000000000001db
        /usr/lib64/libc-2.26.so
    0x00007ffff7a33000  0x00007ffff7a37000  0x00000000000001da
        /usr/lib64/libc-2.26.so
    0x00007ffff7a37000  0x00007ffff7a39000  0x00000000000001de
        /usr/lib64/libc-2.26.so
    0x00007ffff7a3d000  0x00007ffff7bd4000  0x0000000000000000
        /usr/lib64/libm-2.26.so
    0x00007ffff7bd4000  0x00007ffff7dd3000  0x0000000000000197
        /usr/lib64/libm-2.26.so
    0x00007ffff7dd3000  0x00007ffff7dd4000  0x0000000000000196
        /usr/lib64/libm-2.26.so
    0x00007ffff7dd4000  0x00007ffff7dd5000  0x0000000000000197
        /usr/lib64/libm-2.26.so
    0x00007ffff7dd5000  0x00007ffff7dfc000  0x0000000000000000
        /usr/lib64/ld-2.26.so
    0x00007ffff7ffc000  0x00007ffff7ffd000  0x0000000000000027
        /usr/lib64/ld-2.26.so
    0x00007ffff7ffd000  0x00007ffff7ffe000  0x0000000000000028
        /usr/lib64/ld-2.26.so
  CORE                 0x00000200	NT_FPREGSET (floating point registers)
  LINUX                0x00000340	NT_X86_XSTATE (x86 XSAVE extended state)
   description data: 7f 03 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ffffff80 1f 00 00 ffffffff ffffffff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff ffffffff 2f 2f 2f 2f 2f 2f 2f 2f 2f 2f 2f 2f 2f 2f 2f 2f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ffffffff 00 00 00 00 00 00 00 ffffffff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ffffffff 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 74 2f 62 75 69 6c 64 2f 67 6e 75 2f 67 64 62 2f 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 07 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

binutils/

	PR binutils/22490
	PR gas/22492
	* readelf.c (process_notes_at): Add an argument for note
	alignment.  If note alignment is less than 4, use 4 byte
	alignment.
	(process_corefile_note_segments): Pass segment alignment to
	process_notes_at.
	(process_note_sections): Pass section alignment to
	process_notes_at.
	(process_object): Call load_separate_debug_file only if
	e_shstrndx != SHN_UNDEF.

gas/

	PR gas/22492
	* config/obj-elf.c (obj_elf_version): Align note section to 4
	bytes.
	(sco_id): Likewise.
---
 binutils/readelf.c   | 26 ++++++++++++++++++++------
 gas/config/obj-elf.c |  2 ++
 2 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/binutils/readelf.c b/binutils/readelf.c
index 739367d899..04d968f7e2 100644
--- a/binutils/readelf.c
+++ b/binutils/readelf.c
@@ -17904,7 +17904,8 @@ static bfd_boolean
 process_notes_at (Filedata *           filedata,
 		  Elf_Internal_Shdr *  section,
 		  bfd_vma              offset,
-		  bfd_vma              length)
+		  bfd_vma              length,
+		  bfd_vma              align)
 {
   Elf_External_Note * pnotes;
   Elf_External_Note * external;
@@ -17937,6 +17938,14 @@ process_notes_at (Filedata *           filedata,
     printf (_("\nDisplaying notes found at file offset 0x%08lx with length 0x%08lx:\n"),
 	    (unsigned long) offset, (unsigned long) length);
 
+  /* NB: Some note sections may have alignment value of 0 or 1.  gABI
+     specifies that notes should be aligned to 4 bytes in 32-bit
+     objects and to 8 bytes in 64-bit objects.  As a Linux extension,
+     we also support 4 byte alignment in 64-bit objects.  If section
+     alignment is less than 4, we treate alignment as 4 bytes.   */
+  if (align < 4)
+    align = 4;
+
   printf (_("  %-20s %10s\tDescription\n"), _("Owner"), _("Data size"));
 
   end = (char *) pnotes + length;
@@ -17971,11 +17980,11 @@ process_notes_at (Filedata *           filedata,
 	  inote.descsz   = BYTE_GET (external->descsz);
 	  inote.descdata = ((char *) external
 			    + ELF_NOTE_DESC_OFFSET (inote.namesz,
-						    section->sh_addralign));
+						    align));
 	  inote.descpos  = offset + (inote.descdata - (char *) pnotes);
 	  next = ((char *) external
 		  + ELF_NOTE_NEXT_OFFSET (inote.namesz, inote.descsz,
-					  section->sh_addralign));
+					  align));
 	}
       else
 	{
@@ -18077,7 +18086,8 @@ process_corefile_note_segments (Filedata * filedata)
       if (segment->p_type == PT_NOTE)
 	if (! process_notes_at (filedata, NULL,
 				(bfd_vma) segment->p_offset,
-				(bfd_vma) segment->p_filesz))
+				(bfd_vma) segment->p_filesz,
+				(bfd_vma) segment->p_align))
 	  res = FALSE;
     }
 
@@ -18181,7 +18191,8 @@ process_note_sections (Filedata * filedata)
 	{
 	  if (! process_notes_at (filedata, section,
 				  (bfd_vma) section->sh_offset,
-				  (bfd_vma) section->sh_size))
+				  (bfd_vma) section->sh_size,
+				  (bfd_vma) section->sh_addralign))
 	    res = FALSE;
 	  n++;
 	}
@@ -18556,7 +18567,10 @@ process_object (Filedata * filedata)
   if (! process_version_sections (filedata))
     res = FALSE;
 
-  separates = load_separate_debug_file (filedata, filedata->file_name);
+  if (filedata->file_header.e_shstrndx != SHN_UNDEF)
+    separates = load_separate_debug_file (filedata, filedata->file_name);
+  else
+    separates = NULL;
 
   if (! process_section_contents (filedata))
     res = FALSE;
diff --git a/gas/config/obj-elf.c b/gas/config/obj-elf.c
index 3f641f4394..768812748e 100644
--- a/gas/config/obj-elf.c
+++ b/gas/config/obj-elf.c
@@ -1829,6 +1829,7 @@ obj_elf_version (int ignore ATTRIBUTE_UNUSED)
       bfd_set_section_flags (stdoutput,
 			     note_secp,
 			     SEC_HAS_CONTENTS | SEC_READONLY);
+      bfd_set_section_alignment (stdoutput, note_secp, 2);
 
       /* Process the version string.  */
       len = strlen (name) + 1;
@@ -2684,6 +2685,7 @@ sco_id (void)
   bfd_set_section_flags (stdoutput,
 			 note_secp,
 			 SEC_HAS_CONTENTS | SEC_READONLY);
+  bfd_set_section_alignment (stdoutput, note_secp, 2);
 
   /* process the version string */
 
-- 
2.14.3

Follow-Ups:
- Re: PATCH] Properly handle note sections and segments
  - From: H.J. Lu

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