Re: [PATCH] x86: Delay setting the iplt section alignment

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Fri, Nov 30, 2018 at 05:55:43AM -0800, H.J. Lu wrote:
> On Fri, Nov 30, 2018 at 08:01:48PM +1030, Alan Modra wrote:
> > On Thu, Nov 29, 2018 at 02:57:36PM -0800, H.J. Lu wrote:
> > > To work around it, we set alignment of the output section to
> > > 1 if there is only one excluded input section.
> > 
> > This is a tricky problem to solve, and I suspect what you're doing
> > here is not correct in general, even for a single input section.  For
> > example, what happens if the output section statement specifies
> > alignment?
> > 
> > I've faced something similar before on ppc64 with stub sections, and
> > the solution I found was to create the section with minimal alignment,
> > then increase to the desired alignment when the section is found to be
> > non-empty.  That idea might work for you too.
> > 
> 
> Like this.
> 
> Thanks.
> 
> H.J.
> ---
> >From a58108461c4e9710197c12f29cfa6c94b5db240c Mon Sep 17 00:00:00 2001
> From: "H.J. Lu" <hjl.tools@gmail.com>
> Date: Wed, 28 Nov 2018 15:29:42 -0800
> Subject: [PATCH] x86: Delay setting the iplt section alignment
> 
> Delay setting its alignment until we know it is non-empty.  Otherwise an
> empty iplt section may change vma and lma of the following sections, which
> triggers moving dot of the following section backwards, resulting in a
> warning and section lma not being set properly.  It later leads to a
> "File truncated" error.
> 
> bfd/
> 
> 	PR ld/23930
> 	* elfxx-x86.c (_bfd_x86_elf_size_dynamic_sections): Update
> 	the iplt section alignment if it is non-empty.
> 	(_bfd_x86_elf_link_setup_gnu_properties): Delay setting the iplt
> 	section alignment.
> 

This is the patch I am checking in.

H.J.
---
>From b44ee3a8cf21294eeb079ffbada7eeb559a9c6b4 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Sat, 1 Dec 2018 05:42:33 -0800
Subject: [PATCH] x86: Delay setting the iplt section alignment

Delay setting its alignment until we know it is non-empty.  Otherwise an
empty iplt section may change vma and lma of the following sections, which
triggers moving dot of the following section backwards, resulting in a
warning and section lma not being set properly.  It later leads to a
"File truncated" error.

bfd/

	PR ld/23930
	* elfxx-x86.c (_bfd_x86_elf_size_dynamic_sections): Update
	the iplt section alignment if it is non-empty.
	(_bfd_x86_elf_link_setup_gnu_properties): Set plt.iplt_alignment
	and delay setting the iplt section alignment.
	* elfxx-x86.h (elf_x86_plt_layout): Add iplt_alignment.

ld/

	PR ld/23930
	* testsuite/ld-i386/i386.exp: Run pr23930.
	* testsuite/ld-i386/pr23930.d: New file.
	* testsuite/ld-x86-64/pr23930-32.t: Likewise.
	* testsuite/ld-x86-64/pr23930-x32.d: Likewise.
	* testsuite/ld-x86-64/pr23930.d: Likewise.
	* testsuite/ld-x86-64/pr23930.t: Likewise.
	* testsuite/ld-x86-64/pr23930a.s: Likewise.
	* testsuite/ld-x86-64/pr23930b.s: Likewise.
	* testsuite/ld-x86-64/x86-64.exp: Run pr23930 and pr23930-x32.
---
 bfd/ChangeLog                        |  9 +++++++++
 bfd/elfxx-x86.c                      | 30 +++++++++++++++++++++-------
 bfd/elfxx-x86.h                      |  3 +++
 ld/ChangeLog                         | 13 ++++++++++++
 ld/testsuite/ld-i386/i386.exp        |  1 +
 ld/testsuite/ld-i386/pr23930.d       | 11 ++++++++++
 ld/testsuite/ld-x86-64/pr23930-32.t  | 10 ++++++++++
 ld/testsuite/ld-x86-64/pr23930-x32.d | 11 ++++++++++
 ld/testsuite/ld-x86-64/pr23930.d     | 11 ++++++++++
 ld/testsuite/ld-x86-64/pr23930.t     | 10 ++++++++++
 ld/testsuite/ld-x86-64/pr23930a.s    |  7 +++++++
 ld/testsuite/ld-x86-64/pr23930b.s    | 14 +++++++++++++
 ld/testsuite/ld-x86-64/x86-64.exp    |  2 ++
 13 files changed, 125 insertions(+), 7 deletions(-)
 create mode 100644 ld/testsuite/ld-i386/pr23930.d
 create mode 100644 ld/testsuite/ld-x86-64/pr23930-32.t
 create mode 100644 ld/testsuite/ld-x86-64/pr23930-x32.d
 create mode 100644 ld/testsuite/ld-x86-64/pr23930.d
 create mode 100644 ld/testsuite/ld-x86-64/pr23930.t
 create mode 100644 ld/testsuite/ld-x86-64/pr23930a.s
 create mode 100644 ld/testsuite/ld-x86-64/pr23930b.s

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index e0eb155988..3210b0c380 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,12 @@
+2018-12-01  H.J. Lu  <hongjiu.lu@intel.com>
+
+	PR ld/23930
+	* elfxx-x86.c (_bfd_x86_elf_size_dynamic_sections): Update
+	the iplt section alignment if it is non-empty.
+	(_bfd_x86_elf_link_setup_gnu_properties): Set plt.iplt_alignment
+	and delay setting the iplt section alignment.
+	* elfxx-x86.h (elf_x86_plt_layout): Add iplt_alignment.
+
 2018-11-30  Nick Clifton  <nickc@redhat.com>
 
 	PR 23942
diff --git a/bfd/elfxx-x86.c b/bfd/elfxx-x86.c
index 05f5c6a2f9..40aac664f4 100644
--- a/bfd/elfxx-x86.c
+++ b/bfd/elfxx-x86.c
@@ -1275,6 +1275,14 @@ _bfd_x86_elf_size_dynamic_sections (bfd *output_bfd,
       if ((s->flags & SEC_HAS_CONTENTS) == 0)
 	continue;
 
+      /* NB: Initially, the iplt section has minimal alignment to
+	 avoid moving dot of the following section backwards when
+	 it is empty.  Update its section alignment now since it
+	 is non-empty.  */
+      if (s == htab->elf.iplt)
+	bfd_set_section_alignment (s->owner, s,
+				   htab->plt.iplt_alignment);
+
       /* Allocate memory for the section contents.  We use bfd_zalloc
 	 here in case unused entries are not reclaimed before the
 	 section's contents are written out.  This should not happen,
@@ -2907,15 +2915,23 @@ error_alignment:
 	}
     }
 
-  if (normal_target)
+  /* The .iplt section is used for IFUNC symbols in static
+     executables.  */
+  sec = htab->elf.iplt;
+  if (sec != NULL)
     {
-      /* The .iplt section is used for IFUNC symbols in static
-	 executables.  */
-      sec = htab->elf.iplt;
-      if (sec != NULL
-	  && !bfd_set_section_alignment (sec->owner, sec,
-					 plt_alignment))
+      /* NB: Delay setting its alignment until we know it is non-empty.
+	 Otherwise an empty iplt section may change vma and lma of the
+	 following sections, which triggers moving dot of the following
+	 section backwards, resulting in a warning and section lma not
+	 being set properly.  It later leads to a "File truncated"
+	 error.  */
+      if (!bfd_set_section_alignment (sec->owner, sec, 0))
 	goto error_alignment;
+
+      htab->plt.iplt_alignment = (normal_target
+				  ? plt_alignment
+				  : bed->plt_alignment);
     }
 
   return pbfd;
diff --git a/bfd/elfxx-x86.h b/bfd/elfxx-x86.h
index 964843822e..d153623d3e 100644
--- a/bfd/elfxx-x86.h
+++ b/bfd/elfxx-x86.h
@@ -389,6 +389,9 @@ struct elf_x86_plt_layout
      This is only used for x86-64.  */
   unsigned int plt_got_insn_size;
 
+  /* Alignment of the .iplt section.  */
+  unsigned int iplt_alignment;
+
   /* .eh_frame covering the .plt section.  */
   const bfd_byte *eh_frame_plt;
   unsigned int eh_frame_plt_size;
diff --git a/ld/ChangeLog b/ld/ChangeLog
index e203edcf2d..80fd06c1ca 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,16 @@
+2018-12-01  H.J. Lu  <hongjiu.lu@intel.com>
+
+	PR ld/23930
+	* testsuite/ld-i386/i386.exp: Run pr23930.
+	* testsuite/ld-i386/pr23930.d: New file.
+	* testsuite/ld-x86-64/pr23930-32.t: Likewise.
+	* testsuite/ld-x86-64/pr23930-x32.d: Likewise.
+	* testsuite/ld-x86-64/pr23930.d: Likewise.
+	* testsuite/ld-x86-64/pr23930.t: Likewise.
+	* testsuite/ld-x86-64/pr23930a.s: Likewise.
+	* testsuite/ld-x86-64/pr23930b.s: Likewise.
+	* testsuite/ld-x86-64/x86-64.exp: Run pr23930 and pr23930-x32.
+---
 2018-11-30  Alan Modra  <amodra@gmail.com>
 
 	* testsuite/ld-powerpc/pr23937.d,
diff --git a/ld/testsuite/ld-i386/i386.exp b/ld/testsuite/ld-i386/i386.exp
index 76577c4fcb..f86a54d27a 100644
--- a/ld/testsuite/ld-i386/i386.exp
+++ b/ld/testsuite/ld-i386/i386.exp
@@ -482,6 +482,7 @@ run_dump_test "pr23486b"
 run_dump_test "pr23486c"
 run_dump_test "pr23486d"
 run_dump_test "pr23854"
+run_dump_test "pr23930"
 
 if { !([istarget "i?86-*-linux*"]
        || [istarget "i?86-*-gnu*"]
diff --git a/ld/testsuite/ld-i386/pr23930.d b/ld/testsuite/ld-i386/pr23930.d
new file mode 100644
index 0000000000..e9da5106eb
--- /dev/null
+++ b/ld/testsuite/ld-i386/pr23930.d
@@ -0,0 +1,11 @@
+#source: ../ld-x86-64/pr23930a.s
+#source: ../ld-x86-64/pr23930b.s
+#as: --32
+#ld: -m elf_i386 -z separate-code -z norelro -T ../ld-x86-64/pr23930-32.t
+#objdump: --disassemble=main
+
+#...
+[a-f0-9]+ <main>:
+[a-f0-9]+:	31 c0                	xor    %eax,%eax
+[a-f0-9]+:	c3                   	ret    
+#pass
diff --git a/ld/testsuite/ld-x86-64/pr23930-32.t b/ld/testsuite/ld-x86-64/pr23930-32.t
new file mode 100644
index 0000000000..29b5309f48
--- /dev/null
+++ b/ld/testsuite/ld-x86-64/pr23930-32.t
@@ -0,0 +1,10 @@
+PHDRS {
+ text PT_LOAD;
+}
+
+SECTIONS
+{
+ . = (0x8000000f + ALIGN(0x1000000, 0x1000000));
+ .text : AT(ADDR(.text) - 0x8000000f) {
+ } :text
+}
diff --git a/ld/testsuite/ld-x86-64/pr23930-x32.d b/ld/testsuite/ld-x86-64/pr23930-x32.d
new file mode 100644
index 0000000000..b01d2b961c
--- /dev/null
+++ b/ld/testsuite/ld-x86-64/pr23930-x32.d
@@ -0,0 +1,11 @@
+#source: pr23930a.s
+#source: pr23930b.s
+#as: --x32
+#ld: -m elf32_x86_64 -z separate-code -z norelro -T pr23930-32.t
+#objdump: --disassemble=main
+
+#...
+[a-f0-9]+ <main>:
+[a-f0-9]+:	31 c0                	xor    %eax,%eax
+[a-f0-9]+:	c3                   	retq   
+#pass
diff --git a/ld/testsuite/ld-x86-64/pr23930.d b/ld/testsuite/ld-x86-64/pr23930.d
new file mode 100644
index 0000000000..c849b68c45
--- /dev/null
+++ b/ld/testsuite/ld-x86-64/pr23930.d
@@ -0,0 +1,11 @@
+#source: pr23930a.s
+#source: pr23930b.s
+#as: --64
+#ld: -m elf_x86_64 -z separate-code -z norelro -T pr23930.t
+#objdump: --disassemble=main
+
+#...
+[a-f0-9]+ <main>:
+[a-f0-9]+:	31 c0                	xor    %eax,%eax
+[a-f0-9]+:	c3                   	retq   
+#pass
diff --git a/ld/testsuite/ld-x86-64/pr23930.t b/ld/testsuite/ld-x86-64/pr23930.t
new file mode 100644
index 0000000000..2255ed3173
--- /dev/null
+++ b/ld/testsuite/ld-x86-64/pr23930.t
@@ -0,0 +1,10 @@
+PHDRS {
+ text PT_LOAD;
+}
+
+SECTIONS
+{
+ . = (0xffffffff8000000f + ALIGN(0x1000000, 0x1000000));
+ .text : AT(ADDR(.text) - 0xffffffff8000000f) {
+ } :text
+}
diff --git a/ld/testsuite/ld-x86-64/pr23930a.s b/ld/testsuite/ld-x86-64/pr23930a.s
new file mode 100644
index 0000000000..e1679a9af4
--- /dev/null
+++ b/ld/testsuite/ld-x86-64/pr23930a.s
@@ -0,0 +1,7 @@
+	.text
+	.globl	other
+	.type	other, @function
+other:
+	xorl	%eax, %eax
+	ret
+	.size	other, .-other
diff --git a/ld/testsuite/ld-x86-64/pr23930b.s b/ld/testsuite/ld-x86-64/pr23930b.s
new file mode 100644
index 0000000000..e4859c7747
--- /dev/null
+++ b/ld/testsuite/ld-x86-64/pr23930b.s
@@ -0,0 +1,14 @@
+	.text
+	.globl	orig
+	.type	orig, @function
+orig:
+	xorl	%eax, %eax
+	ret
+	.size	orig, .-orig
+	.section	.text.startup,"ax",@progbits
+	.globl	main
+	.type	main, @function
+main:
+	xorl	%eax, %eax
+	ret
+	.size	main, .-main
diff --git a/ld/testsuite/ld-x86-64/x86-64.exp b/ld/testsuite/ld-x86-64/x86-64.exp
index 8e5348dfea..b51ad7cebc 100644
--- a/ld/testsuite/ld-x86-64/x86-64.exp
+++ b/ld/testsuite/ld-x86-64/x86-64.exp
@@ -422,6 +422,8 @@ run_dump_test "pr23486c-x32"
 run_dump_test "pr23486d"
 run_dump_test "pr23486d-x32"
 run_dump_test "pr23854"
+run_dump_test "pr23930"
+run_dump_test "pr23930-x32"
 
 if { ![istarget "x86_64-*-linux*"] && ![istarget "x86_64-*-nacl*"]} {
     return
-- 
2.19.2