[PATCH] Use linker script to remove unnecessary sections

[PATCH] Use linker script to remove unnecessary sections

[Bean]

Hi,

This patch use customized linker script to build *.img and *.mod
files, it should remove unnecessary sections created by the compiler.


2007-12-14  Bean  <bean123ch@gmail.com>

	* conf/i386-pc.rmk (COMMON_LDFLAGS): Use ldscript to link.

	* aclocal.m4 (grub_PROG_OBJCOPY_ABSOLUTE): Test ldscript.

	* configure.ac : Remove the '--build-id=none' flag.

	* ldscript : New file.


Index: conf/i386-pc.rmk
===================================================================
RCS file: /sources/grub/grub2/conf/i386-pc.rmk,v
retrieving revision 1.94
diff -u -p -r1.94 i386-pc.rmk
--- conf/i386-pc.rmk	18 Nov 2007 06:41:45 -0000	1.94
+++ conf/i386-pc.rmk	14 Dec 2007 11:51:13 -0000
@@ -2,10 +2,10 @@

 COMMON_ASFLAGS = -nostdinc -fno-builtin -m32
 COMMON_CFLAGS = -fno-builtin -mrtd -mregparm=3 -m32
-COMMON_LDFLAGS = -m32 -nostdlib
+COMMON_LDFLAGS = -m32 -nostdlib -T "${srcdir}/ldscript"

 # Images.
 pkgdata_IMAGES = boot.img diskboot.img kernel.img pxeboot.img
Index: aclocal.m4
===================================================================
RCS file: /sources/grub/grub2/aclocal.m4,v
retrieving revision 1.7
diff -u -p -r1.7 aclocal.m4
--- aclocal.m4	25 Nov 2007 02:01:30 -0000	1.7
+++ aclocal.m4	14 Dec 2007 11:51:14 -0000
@@ -57,7 +57,7 @@ else
 fi
 grub_cv_prog_objcopy_absolute=yes
 for link_addr in 2000 8000 7C00; do
-  if AC_TRY_COMMAND([${CC-cc} ${CFLAGS} ${LDFLAGS} -nostdlib -Wl,-N
-Wl,-Ttext -Wl,$link_addr conftest.o -o conftest.exec]); then :
+  if AC_TRY_COMMAND([${CC-cc} ${CFLAGS} -nostdlib -Wl,-N -Wl,-T
"-Wl,${srcdir}/ldscript" -Wl,-Ttext -Wl,$link_addr conftest.o -o
conftest.exec]); then :
   else
     AC_MSG_ERROR([${CC-cc} cannot link at address $link_addr])
   fi
Index: configure.ac
===================================================================
RCS file: /sources/grub/grub2/configure.ac,v
retrieving revision 1.40
diff -u -p -r1.40 configure.ac
--- configure.ac	25 Nov 2007 02:01:30 -0000	1.40
+++ configure.ac	14 Dec 2007 11:51:14 -0000
@@ -229,16 +229,6 @@ if test "x$target_m32" = x1; then
   TARGET_LDFLAGS="$TARGET_LDFLAGS -m32"
 fi

-AC_MSG_CHECKING([whether the linker accepts `--build-id=none'])
-save_LDFLAGS="$LDFLAGS"
-LDFLAGS="$LDFLAGS -Wl,--build-id=none"
-AC_TRY_LINK(, , build_id_flag=yes, build_id_flag=no)
-AC_MSG_RESULT([$build_id_flag])
-LDFLAGS="$save_LDFLAGS"
-if test "x$build_id_flag" = xyes; then
-  TARGET_LDFLAGS="$TARGET_LDFLAGS -Wl,--build-id=none"
-fi
-
 #
 # Compiler features.
 #
Index: ldscript
===================================================================
RCS file: /sources/grub/grub2/ldscript,v
diff -Nu ldscript
--- /dev/null	2007-12-15 02:52:31.284046226 +0800
+++ ldscript	2007-12-14 19:37:39.546875000 +0800
@@ -0,0 +1,12 @@
+SECTIONS
+{
+  .text : { *(.text) } =0x90909090
+  .rodata : { *(.rodata .rodata.*) }
+  .data : { *(.data) }
+  PROVIDE(__bss_start = .);
+  .bss : { *(.bss) *(COMMON) }
+  PROVIDE(end = .);
+  .modname : { *(.modname) }
+  .moddep : { *(.moddep) }
+  /DISCARD/ : { *(*) }
+}

-- 
Bean

Re: [PATCH] Use linker script to remove unnecessary sections

[Pavel Roskin]

Quoting Bean <bean123ch@gmail.com>:

> Hi,
>
> This patch use customized linker script to build *.img and *.mod
> files, it should remove unnecessary sections created by the compiler.

Thanks!  Looks good to me.  Actually, if we stop using objcopy, we  
don't need to test it at all.  Or we can reuse the test to test ld in  
place of objcopy.

I tend to prefer the removal of grub_PROG_OBJCOPY_ABSOLUTE, as it's  
designed to find a specific bug in some old version of objcopy, and if  
we discover any issues with ld (I hope not), we'll have to use  
different tests to detect them.

We may want to use architecture specific ld scripts, but that can be  
corrected in further patches.

-- 
Regards,
Pavel Roskin

Re: [PATCH] Use linker script to remove unnecessary sections

[Christian Franke]

Bean wrote:
> ...
> diff -u -p -r1.7 aclocal.m4
> --- aclocal.m4	25 Nov 2007 02:01:30 -0000	1.7
> +++ aclocal.m4	14 Dec 2007 11:51:14 -0000
> @@ -57,7 +57,7 @@ else
>  fi
>  grub_cv_prog_objcopy_absolute=yes
>  for link_addr in 2000 8000 7C00; do
> -  if AC_TRY_COMMAND([${CC-cc} ${CFLAGS} ${LDFLAGS} -nostdlib -Wl,-N
> -Wl,-Ttext -Wl,$link_addr conftest.o -o conftest.exec]); then :
> +  if AC_TRY_COMMAND([${CC-cc} ${CFLAGS} -nostdlib -Wl,-N -Wl,-T
> "-Wl,${srcdir}/ldscript" -Wl,-Ttext -Wl,$link_addr conftest.o -o
> conftest.exec]); then :
>   

Selecting the builtin "-N" script first has no effect if a custom script 
is specified later. Therefore, "-Wl,-N" is IMO no longer necessary.


Pavel Roskin wrote:
> ...
> We may want to use architecture specific ld scripts, but that can be 
> corrected in further patches.

See "[PATCH] Build on Cygwin" for a working example on how to select a 
platform specific linker script in configure.ac. This can be easily 
extended, e.g. test more specific scripts first:

  for f in \
    ${target_cpu}-${platform}-${target_os} \
    ${target_cpu}-${platform} \
    ${target_cpu}; do
    if test -f "${srcdir}/conf/$f-img-ld.sc"; then ...


Christian

Re: [PATCH] Use linker script to remove unnecessary sections

[Robert Millan]

On Fri, Dec 14, 2007 at 08:11:36PM +0800, Bean wrote:
> Hi,
> 
> This patch use customized linker script to build *.img and *.mod
> files, it should remove unnecessary sections created by the compiler.
> 
> 
> 2007-12-14  Bean  <bean123ch@gmail.com>
> 
> 	* conf/i386-pc.rmk (COMMON_LDFLAGS): Use ldscript to link.
> 
> 	* aclocal.m4 (grub_PROG_OBJCOPY_ABSOLUTE): Test ldscript.
> 
> 	* configure.ac : Remove the '--build-id=none' flag.

This probably breaks other targets than i386-pc.  linuxbios and ieee1275
both use ELF.

-- 
Robert Millan

<GPLv2> I know my rights; I want my phone call!
<DRM> What use is a phone call, if you are unable to speak?
(as seen on /.)

Re: [PATCH] Use linker script to remove unnecessary sections

[Pavel Roskin]

Quoting Robert Millan <rmh@aybabtu.com>:

> On Fri, Dec 14, 2007 at 08:11:36PM +0800, Bean wrote:
>> Hi,
>>
>> This patch use customized linker script to build *.img and *.mod
>> files, it should remove unnecessary sections created by the compiler.
>>
>>
>> 2007-12-14  Bean  <bean123ch@gmail.com>
>>
>> 	* conf/i386-pc.rmk (COMMON_LDFLAGS): Use ldscript to link.
>>
>> 	* aclocal.m4 (grub_PROG_OBJCOPY_ABSOLUTE): Test ldscript.
>>
>> 	* configure.ac : Remove the '--build-id=none' flag.
>
> This probably breaks other targets than i386-pc.  linuxbios and ieee1275
> both use ELF.

But they don't use objcopy, they use strip.  The goal is to switch  
i386-pc from the buggy and simple objcopy to more powerful and  
flexible ld.  The same could be done to replace strip for other  
platforms while keeping ELF format for the output.

I agree that we should avoid naming highly target-specific linker  
scripts in a generic way.  "i386-pc.ld" might be a better name.  The  
linker script for modules perhaps could be generic, but this is for  
*.img files.

-- 
Regards,
Pavel Roskin

Re: [PATCH] Use linker script to remove unnecessary sections

[Robert Millan]

On Sun, Dec 16, 2007 at 11:29:31AM -0500, Pavel Roskin wrote:
> 
> I agree that we should avoid naming highly target-specific linker  
> scripts in a generic way.  "i386-pc.ld" might be a better name.

or i386/pc/ld (more consistent with the rest of grub)

-- 
Robert Millan

<GPLv2> I know my rights; I want my phone call!
<DRM> What use is a phone call, if you are unable to speak?
(as seen on /.)

Re: [PATCH] Use linker script to remove unnecessary sections

[Christian Franke]

Robert Millan wrote:
> On Sun, Dec 16, 2007 at 11:29:31AM -0500, Pavel Roskin wrote:
>   
>> I agree that we should avoid naming highly target-specific linker  
>> scripts in a generic way.  "i386-pc.ld" might be a better name.
>>     
>
> or i386/pc/ld (more consistent with the rest of grub)
>
>   

or "i386/pc/img.ld" (ld script to produce .img files).

Should this dir structure reside in "conf" ? This scheme is not yet used 
for the *mk files in this directory.

Christian