[PATCH 7/7] Use --build-id ld option

[PATCH 7/7] Use --build-id ld option

[Roland McGrath]

This change passes the --build-id when linking the kernel and when
linking modules, if ld supports it.  This is a new GNU ld option that
synthesizes an ELF note section inside the read-only data.  The note in
this section contains unique identifying bits called the "build ID",
which are generated so as to be different for any two linked ELF files
that aren't identical.  The build ID can be recovered from stripped
files, memory dumps, etc. and used to look up the original program
built, locate debuginfo or other details or history associated with it.
For normal program linking, the compiler passes --build-id to ld by
default, but the option is needed when using ld directly as we do.

Signed-off-by: Roland McGrath <roland@redhat.com>
---
 Makefile |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/Makefile b/Makefile
index 88b2252..1e11ceb 100644
--- a/Makefile
+++ b/Makefile
@@ -514,6 +514,12 @@ CFLAGS += $(call cc-option,-Wdeclaration-after-statement,)
 # disable pointer signed / unsigned warnings in gcc 4.0
 CFLAGS += $(call cc-option,-Wno-pointer-sign,)
 
+# Use --build-id when available.
+LDFLAGS_BUILD_ID = $(patsubst -Wl$(comma)%,%,\
+			      $(call ld-option, -Wl$(comma)--build-id,))
+LDFLAGS_MODULE += $(LDFLAGS_BUILD_ID)
+LDFLAGS_vmlinux += $(LDFLAGS_BUILD_ID)
+
 # Default kernel image to build when no specific target is given.
 # KBUILD_IMAGE may be overruled on the command line or
 # set in the environment

Re: [PATCH 7/7] Use --build-id ld option

[Jeremy Fitzhardinge]

Roland McGrath wrote:
> This change passes the --build-id when linking the kernel and when
> linking modules, if ld supports it.  This is a new GNU ld option that
> synthesizes an ELF note section inside the read-only data.  The note in
> this section contains unique identifying bits called the "build ID",
> which are generated so as to be different for any two linked ELF files
> that aren't identical.

Does this mean that performing the same link twice *will* produce an 
identical result?

    J

Re: [PATCH 7/7] Use --build-id ld option

[Roland McGrath]

> Does this mean that performing the same link twice *will* produce an 
> identical result?

Yes.

Re: [PATCH 7/7] Use --build-id ld option

[Adrian Bunk]

On Wed, Jul 11, 2007 at 11:24:58PM -0700, Roland McGrath wrote:
> > Does this mean that performing the same link twice *will* produce an 
> > identical result?
> 
> Yes.

But note that twice compiling a kernel with the same .config will result 
in a different one.

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

Re: [PATCH 7/7] Use --build-id ld option

[Jeremy Fitzhardinge]

Adrian Bunk wrote:
> But note that twice compiling a kernel with the same .config will result 
> in a different one.

Is that true even if you reset the .version counter each time?  I'm 
thinking of product build systems, in which they value being able to 
reproduce the same build (ideally, bit for bit).

    J

Re: [PATCH 7/7] Use --build-id ld option

[Adrian Bunk]

On Fri, Jul 13, 2007 at 06:26:35PM -0700, Jeremy Fitzhardinge wrote:
> Adrian Bunk wrote:
>> But note that twice compiling a kernel with the same .config will result 
>> in a different one.
>
> Is that true even if you reset the .version counter each time?  I'm 
> thinking of product build systems, in which they value being able to 
> reproduce the same build (ideally, bit for bit).

$ grep UTS_VERSION include/linux/compile.h
#define UTS_VERSION "#3 Sat Jul 14 03:21:18 CEST 2007"
$ 

>    J

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed