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Re: PATCH: Convert mov to lea for loading local function address

From: "H.J. Lu" <hjl dot tools at gmail dot com>
To: Binutils <binutils at sourceware dot org>
Cc: Richard Henderson <rth at redhat dot com>
Date: Fri, 31 Aug 2012 19:48:02 -0700
Subject: Re: PATCH: Convert mov to lea for loading local function address
References: <20120831042236.GA19539@intel.com> <CAMe9rOpeuHRDhVXURydFDk4nX1CmZDGSiVjiHERNjk9E0-ovWQ@mail.gmail.com> <CAMe9rOpM3p7-1uWf1kYcA7KcLcFyD3Z-vKgymfSB60idE-m1jw@mail.gmail.com>

On Fri, Aug 31, 2012 at 6:03 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Fri, Aug 31, 2012 at 1:44 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> On Thu, Aug 30, 2012 at 9:22 PM, H.J. Lu <hongjiu.lu@intel.com> wrote:
>>> Hi,
>>>
>>> I am checking in this patch to convert move mov to lea for loading local
>>> function address.
>>>
>>> bfd/
>>>
>>> 2012-08-30  H.J. Lu  <hongjiu.lu@intel.com>
>>>
>>>         * elf32-i386.c (elf_i386_relocate_section): Convert
>>>         "mov foo@GOT(%reg), %reg" to "lea foo@GOTOFF(%reg), %reg"
>>>         for local symbols.
>>>
>>>         * elf64-x86-64.c (elf_x86_64_relocate_section): Convert
>>>         "mov foo@GOTPCREL(%rip), %reg" to "lea foo@GOTOFF(%reg), %reg"
>>>         for local symbols.
>>>
>>
>> Hi,
>>
>> I checked in this patch to move mov->lea conversion to
>> size_dynamic_sections so that we can remove the unused
>> GOT entries.
>>
>
> It turned out that overdid it for _DYNAMIC.  Glibc ld.so has
>
> /* Return the link-time address of _DYNAMIC.  Conveniently, this is the
>    first element of the GOT.  This must be inlined in a function which
>    uses global data.  */
> static inline ElfW(Addr) __attribute__ ((unused))
> elf_machine_dynamic (void)
>
> We must avoid optimizing _DYNAMIC.
>

I am checking in this.

-- 
H.J.
---
bfd/

2012-08-31  H.J. Lu  <hongjiu.lu@intel.com>

	* elf32-i386.c (elf_i386_convert_mov_to_lea): Don't optimize
	_DYNAMIC.
	* elf64-x86-64.c (elf_x86_64_convert_mov_to_lea): Likewise.

ld/testsuite/

2012-08-31  H.J. Lu  <hongjiu.lu@intel.com>

	* ld-i386/i386.exp: Run mov1a, mov1b.
	* ld-x86-64/x86-64.exp: Run mov1a, mov1b, mov1c, mov1d.

	* ld-i386/mov1.s: New file.
	* ld-i386/mov1a.d: Likewise.
	* ld-i386/mov1b.d: Likewise.
	* ld-x86-64/mov1.s: Likewise.
	* ld-x86-64/mov1a.d: Likewise.
	* ld-x86-64/mov1b.d: Likewise.
	* ld-x86-64/mov1c.d: Likewise.
	* ld-x86-64/mov1d.d: Likewise.

diff --git a/bfd/elf32-i386.c b/bfd/elf32-i386.c
index c9bc694..eab963c 100644
--- a/bfd/elf32-i386.c
+++ b/bfd/elf32-i386.c
@@ -2631,9 +2631,11 @@ elf_i386_convert_mov_to_lea (bfd *abfd, asection *sec,
 	     || h->root.type == bfd_link_hash_warning)
 	h = (struct elf_link_hash_entry *) h->root.u.i.link;

-      /* STT_GNU_IFUNC must keep R_386_GOT32 relocation.  */
+      /* STT_GNU_IFUNC must keep R_386_GOT32 relocation.  We also avoid
+	 optimizing _DYNAMIC since ld.so may use its link-time address.  */
       if (h->def_regular
 	  && h->type != STT_GNU_IFUNC
+	  && strcmp (h->root.root.string, "_DYNAMIC") != 0
 	  && SYMBOL_REFERENCES_LOCAL (link_info, h)
 	  && bfd_get_8 (input_bfd,
 			contents + irel->r_offset - 2) == 0x8b)
diff --git a/bfd/elf64-x86-64.c b/bfd/elf64-x86-64.c
index 0c37cd3..9edc5ae 100644
--- a/bfd/elf64-x86-64.c
+++ b/bfd/elf64-x86-64.c
@@ -2667,9 +2667,12 @@ elf_x86_64_convert_mov_to_lea (bfd *abfd, asection *sec,
 	     || h->root.type == bfd_link_hash_warning)
 	h = (struct elf_link_hash_entry *) h->root.u.i.link;

-      /* STT_GNU_IFUNC must keep R_X86_64_GOTPCREL relocation.  */
+      /* STT_GNU_IFUNC must keep R_X86_64_GOTPCREL relocation.  We also
+	 avoid optimizing _DYNAMIC since ld.so may use its link-time
+	 address.  */
       if (h->def_regular
 	  && h->type != STT_GNU_IFUNC
+	  && strcmp (h->root.root.string, "_DYNAMIC") != 0
 	  && SYMBOL_REFERENCES_LOCAL (link_info, h)
 	  && bfd_get_8 (input_bfd,
 			contents + irel->r_offset - 2) == 0x8b)
diff --git a/ld/testsuite/ld-i386/i386.exp b/ld/testsuite/ld-i386/i386.exp
index adb852e..f5835ac 100644
--- a/ld/testsuite/ld-i386/i386.exp
+++ b/ld/testsuite/ld-i386/i386.exp
@@ -239,6 +239,8 @@ run_dump_test "lea1c"
 run_dump_test "lea1d"
 run_dump_test "lea1e"
 run_dump_test "lea1f"
+run_dump_test "mov1a"
+run_dump_test "mov1b"

 if { !([istarget "i?86-*-linux*"]
        || [istarget "i?86-*-gnu*"]
diff --git a/ld/testsuite/ld-i386/mov1.s b/ld/testsuite/ld-i386/mov1.s
new file mode 100644
index 0000000..c813e71
--- /dev/null
+++ b/ld/testsuite/ld-i386/mov1.s
@@ -0,0 +1,6 @@
+	.text
+	.globl	_start
+	.type	_start, @function
+_start:
+	movl	_DYNAMIC@GOT(%ecx), %eax
+	.size	_start, .-_start
diff --git a/ld/testsuite/ld-i386/mov1a.d b/ld/testsuite/ld-i386/mov1a.d
new file mode 100644
index 0000000..d8ce6b8
--- /dev/null
+++ b/ld/testsuite/ld-i386/mov1a.d
@@ -0,0 +1,13 @@
+#source: mov1.s
+#as: --32
+#ld: -shared -melf_i386
+#objdump: -dw
+
+.*: +file format .*
+
+
+Disassembly of section .text:
+
+#...
+[ 	]*[a-f0-9]+:	8b 81 ([0-9a-f]{2} ){4} *	mov    -0x[a-f0-9]+\(%ecx\),%eax
+#pass
diff --git a/ld/testsuite/ld-i386/mov1b.d b/ld/testsuite/ld-i386/mov1b.d
new file mode 100644
index 0000000..583dfc8
--- /dev/null
+++ b/ld/testsuite/ld-i386/mov1b.d
@@ -0,0 +1,13 @@
+#source: mov1.s
+#as: --32
+#ld: -pie -melf_i386
+#objdump: -dw
+
+.*: +file format .*
+
+
+Disassembly of section .text:
+
+#...
+[ 	]*[a-f0-9]+:	8b 81 ([0-9a-f]{2} ){4} *	mov    -0x[a-f0-9]+\(%ecx\),%eax
+#pass
diff --git a/ld/testsuite/ld-x86-64/mov1.s b/ld/testsuite/ld-x86-64/mov1.s
new file mode 100644
index 0000000..2a11b7a
--- /dev/null
+++ b/ld/testsuite/ld-x86-64/mov1.s
@@ -0,0 +1,6 @@
+	.text
+	.globl	_start
+	.type	_start, @function
+_start:
+	movq	_DYNAMIC@GOTPCREL(%rip), %rax
+	.size	_start, .-_start
diff --git a/ld/testsuite/ld-x86-64/mov1a.d b/ld/testsuite/ld-x86-64/mov1a.d
new file mode 100644
index 0000000..df156be
--- /dev/null
+++ b/ld/testsuite/ld-x86-64/mov1a.d
@@ -0,0 +1,13 @@
+#source: mov1.s
+#as: --64
+#ld: -shared -melf_x86_64
+#objdump: -dw
+
+.*: +file format .*
+
+
+Disassembly of section .text:
+
+#...
+[ 	]*[a-f0-9]+:	48 8b 05 ([0-9a-f]{2} ){4} *	mov
0x[a-f0-9]+\(%rip\),%rax        # [a-f0-9]+ <_DYNAMIC\+0x[a-f0-9]+>
+#pass
diff --git a/ld/testsuite/ld-x86-64/mov1b.d b/ld/testsuite/ld-x86-64/mov1b.d
new file mode 100644
index 0000000..2f2f6f5
--- /dev/null
+++ b/ld/testsuite/ld-x86-64/mov1b.d
@@ -0,0 +1,13 @@
+#source: mov1.s
+#as: --64
+#ld: -pie -melf_x86_64
+#objdump: -dw
+
+.*: +file format .*
+
+
+Disassembly of section .text:
+
+#...
+[ 	]*[a-f0-9]+:	48 8b 05 ([0-9a-f]{2} ){4} *	mov
0x[a-f0-9]+\(%rip\),%rax        # [a-f0-9]+ <_DYNAMIC\+0x[a-f0-9]+>
+#pass
diff --git a/ld/testsuite/ld-x86-64/mov1c.d b/ld/testsuite/ld-x86-64/mov1c.d
new file mode 100644
index 0000000..a57e1c1
--- /dev/null
+++ b/ld/testsuite/ld-x86-64/mov1c.d
@@ -0,0 +1,13 @@
+#source: mov1.s
+#as: --x32
+#ld: -shared -melf32_x86_64
+#objdump: -dw
+
+.*: +file format .*
+
+
+Disassembly of section .text:
+
+#...
+[ 	]*[a-f0-9]+:	48 8b 05 ([0-9a-f]{2} ){4} *	mov
0x[a-f0-9]+\(%rip\),%rax        # [a-f0-9]+ <_DYNAMIC\+0x[a-f0-9]+>
+#pass
diff --git a/ld/testsuite/ld-x86-64/mov1d.d b/ld/testsuite/ld-x86-64/mov1d.d
new file mode 100644
index 0000000..955d33e
--- /dev/null
+++ b/ld/testsuite/ld-x86-64/mov1d.d
@@ -0,0 +1,13 @@
+#source: mov1.s
+#as: --x32
+#ld: -pie -melf32_x86_64
+#objdump: -dw
+
+.*: +file format .*
+
+
+Disassembly of section .text:
+
+#...
+[ 	]*[a-f0-9]+:	48 8b 05 ([0-9a-f]{2} ){4} *	mov
0x[a-f0-9]+\(%rip\),%rax        # [a-f0-9]+ <_DYNAMIC\+0x[a-f0-9]+>
+#pass
diff --git a/ld/testsuite/ld-x86-64/x86-64.exp
b/ld/testsuite/ld-x86-64/x86-64.exp
index 7eabf39..1ad54e6 100644
--- a/ld/testsuite/ld-x86-64/x86-64.exp
+++ b/ld/testsuite/ld-x86-64/x86-64.exp
@@ -288,6 +288,10 @@ run_dump_test "lea1i"
 run_dump_test "lea1j"
 run_dump_test "lea1k"
 run_dump_test "lea1l"
+run_dump_test "mov1a"
+run_dump_test "mov1b"
+run_dump_test "mov1c"
+run_dump_test "mov1d"

 # Must be native with the C compiler
 if { [isnative] && [which $CC] != 0 } {

References:
- Re: PATCH: Convert mov to lea for loading local function address
  - From: H.J. Lu

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