Re: [PATCH] Exclude zero size section for RELRO segment match

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

On Fri, Feb 16, 2018 at 3:44 PM, Alan Modra <amodra@gmail.com> wrote:
> On Fri, Feb 16, 2018 at 04:13:04AM -0800, H.J. Lu wrote:
>> On Fri, Feb 16, 2018 at 4:08 AM, Alan Modra <amodra@gmail.com> wrote:
>> > On Thu, Feb 15, 2018 at 03:58:16AM -0800, H.J. Lu wrote:
>> >> When seaching a LOAD segment which overlaps with the RELRO segment, we
>> >> need to check the size of the last non-zero size section in the LOAD
>> >> segment.
>> >
>> > Why?  Do you have a case where the current algorithm goes wrong?
>> >
>>
>> Yes, apply this patch and I get assert in
>> assign_file_positions_for_non_load_sections
>> on x86-64:
>
> On looking at the tbss1 fail, I see a PT_LOAD with a single
> zero length .eh_frame section.  So we have a degenerate PT_LOAD.
> I think the following simpler patch is sufficient.
>
> Your testsuite change is OK, but please check a large set of targets
> before committing in case some targets won't support -z separate-code.
>
>         PR 22845
>         * elf.c (assign_file_positions_for_non_load_sections): Ignore
>         degenerate zero size PT_LOAD segments when finding one overlapping
>         the PT_GNU_RELRO segment.
>
> diff --git a/bfd/elf.c b/bfd/elf.c
> index 397fa62..b069b59 100644
> --- a/bfd/elf.c
> +++ b/bfd/elf.c
> @@ -5897,6 +5897,7 @@ assign_file_positions_for_non_load_sections (bfd *abfd,
>                    lm = lm->next, lp++)
>                 {
>                   if (lp->p_type == PT_LOAD
> +                     && lp->p_memsz != 0
>                       && lm->count != 0
>                       && lm->sections[lm->count - 1]->vma >= start
>                       && lm->sections[0]->vma < end)
>

This patch isn't sufficient.  On x86, with this patch, I got

[hjl@gnu-tools-1 ld]$  ../gas/as-new
-I/export/gnu/import/git/sources/binutils-gdb/ld/testsuite/ld-elf   -o
tmpdir/tbss.o /export/gnu/import/git/sources/binutils-gdb/ld/testsuite/ld-elf/tbss.s
[hjl@gnu-tools-1 ld]$ ../gas/as-new
-I/export/gnu/import/git/sources/binutils-gdb/ld/testsuite/ld-elf   -o
tmpdir/frame.o /export/gnu/import/git/sources/binutils-gdb/ld/testsuite/ld-elf/frame.s
[hjl@gnu-tools-1 ld]$ ./ld-new   -o tmpdir/frame.so -z separate-code
--shared tmpdir/frame.o tmpdir/tbss.o
./ld-new: BFD (GNU Binutils) 2.30.51.20180217 assertion fail
/export/gnu/import/git/sources/binutils-gdb/bfd/elf.c:5917
[hjl@gnu-tools-1 ld]$

My original patch fixes them.

-- 
H.J.

From 04a1a6e280aeada4031b1f89c2c4c35ade8f3679 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Sat, 17 Feb 2018 15:06:32 -0800
Subject: [PATCH] ld: Add -z separate-code tests to frame.exp

On x86, "-z separate-code" leads to assertion fail at bfd/elf.c:5917.

	PR ld/22845
	* testsuite/ld-elf/frame.exp: Add tests for "-z noseparate-code"
	and "-z separate-code".
---
 ld/testsuite/ld-elf/frame.exp | 32 ++++++++++++++++++++++++++------
 1 file changed, 26 insertions(+), 6 deletions(-)

diff --git a/ld/testsuite/ld-elf/frame.exp b/ld/testsuite/ld-elf/frame.exp
index 6cce42deb3..55e6cba529 100644
--- a/ld/testsuite/ld-elf/frame.exp
+++ b/ld/testsuite/ld-elf/frame.exp
@@ -64,13 +64,23 @@ if { ![ld_assemble_flags $as $as_opt $srcdir/$subdir/tbss.s tmpdir/tbss.o ]
     return
 }
 
-if { [ld_link $ld tmpdir/frame.so "--shared tmpdir/frame.o tmpdir/tbss.o"] } {
-    pass "$test1"
+if { [ld_link $ld tmpdir/frame.so "-z noseparate-code --shared tmpdir/frame.o tmpdir/tbss.o"] } {
+    pass "$test1 -z noseparate-code"
 } else {
     if [string match "*shared not supported*" $link_output] {
 	unsupported "-shared is not supported by this target"
     } else {
-	fail "$test1"
+	fail "$test1 -z noseparate-code"
+    }
+}
+
+if { [ld_link $ld tmpdir/frame.so "-z separate-code --shared tmpdir/frame.o tmpdir/tbss.o"] } {
+    pass "$test1 -z separate-code"
+} else {
+    if [string match "*shared not supported*" $link_output] {
+	unsupported "-shared is not supported by this target"
+    } else {
+	fail "$test1 -z separate-code"
     }
 }
 
@@ -79,12 +89,22 @@ if ![ld_assemble_flags $as $as_opt $srcdir/$subdir/table.s tmpdir/table.o ] {
     return
 }
 
-if { [ld_link $ld tmpdir/table.so "--shared tmpdir/table.o tmpdir/tbss.o"] } {
-    pass "$test2"
+if { [ld_link $ld tmpdir/table.so "-z noseparate-code --shared tmpdir/table.o tmpdir/tbss.o"] } {
+    pass "$test2 -z noseparate-code"
+} else {
+    if [string match "*shared not supported*" $link_output] {
+	unsupported "-shared is not supported by this target"
+    } else {
+	fail "$test2 -z noseparate-code"
+    }
+}
+
+if { [ld_link $ld tmpdir/table.so "-z separate-code --shared tmpdir/table.o tmpdir/tbss.o"] } {
+    pass "$test2 -z separate-code"
 } else {
     if [string match "*shared not supported*" $link_output] {
 	unsupported "-shared is not supported by this target"
     } else {
-	fail "$test2"
+	fail "$test2 -z separate-code"
     }
 }
-- 
2.14.3