[GOLD][PATCH] predefined segment symbol _begin

[GOLD][PATCH] predefined segment symbol _begin

[Viktor Kutuzov]

[-- Attachment #1: Type: text/plain, Size: 258 bytes --]

Hello everyone,

Please find attached patch, which adds an additional predefined segment
symbol _begin.

This is used, for example, in the glibc build.

-Viktor.

* gold/defstd.cc: added a new predefined symbol _begin to the
Define_symbol_in_segment array.


[-- Attachment #2: binutils-gold-stddef_begin_symbol.patch --]
[-- Type: text/x-patch, Size: 870 bytes --]

Index: defstd.cc
===================================================================
RCS file: /cvs/src/src/gold/defstd.cc,v
retrieving revision 1.8
diff -u -p -r1.8 defstd.cc
--- defstd.cc	7 Nov 2009 02:02:29 -0000	1.8
+++ defstd.cc	10 Feb 2010 18:48:57 -0000
@@ -189,6 +189,20 @@ const Define_symbol_in_segment in_segmen
     true			// only_if_ref
   },
   {
+    "_begin",	// name
+    elfcpp::PT_LOAD,		// segment_type
+    elfcpp::PF(0),		// segment_flags_set
+    elfcpp::PF(0),		// segment_flags_clear
+    0,				// value
+    0,				// size
+    elfcpp::STT_NOTYPE,		// type
+    elfcpp::STB_GLOBAL,		// binding
+    elfcpp::STV_DEFAULT,	// visibility
+    0,				// nonvis
+    Symbol::SEGMENT_START,	// offset_from_base
+    true			// only_if_ref
+  },
+  {
     "etext",			// name
     elfcpp::PT_LOAD,		// segment_type
     elfcpp::PF_X,		// segment_flags_set

Re: [GOLD][PATCH] predefined segment symbol _begin

[Ian Lance Taylor]

Viktor Kutuzov <vkutuzov@accesssoftek.com> writes:

> Please find attached patch, which adds an additional predefined segment
> symbol _begin.
>
> This is used, for example, in the glibc build.

I don't see anything in the GNU linker which defines a _begin symbol.

Are you sure it isn't coming from a linker script?

Ian

Re: [GOLD][PATCH] predefined segment symbol _begin

[Viktor Kutuzov]

I'm not sure. I have checked the ld scripts, but I didn't find anything
related with it. I looked for the _begin definition in the ld sources
and I got the same result. It looks strange for me, but anyway.
I seen that the _end and _etext symbols were resolved during the build,
but _begin wasn't and I added this description accordingly.

-Viktor.

On Wed, 2010-02-10 at 16:11 -0800, Ian Lance Taylor wrote:
> Viktor Kutuzov <vkutuzov@accesssoftek.com> writes:
> 
> > Please find attached patch, which adds an additional predefined segment
> > symbol _begin.
> >
> > This is used, for example, in the glibc build.
> 
> I don't see anything in the GNU linker which defines a _begin symbol.
> 
> Are you sure it isn't coming from a linker script?
> 
> Ian

Re: [GOLD][PATCH] predefined segment symbol _begin

[Ian Lance Taylor]

Viktor Kutuzov <vkutuzov@accesssoftek.com> writes:

> I'm not sure. I have checked the ld scripts, but I didn't find anything
> related with it. I looked for the _begin definition in the ld sources
> and I got the same result. It looks strange for me, but anyway.
> I seen that the _end and _etext symbols were resolved during the build,
> but _begin wasn't and I added this description accordingly.

We're going to need to track this down.  I don't want to have gold
start defining a symbol which the GNU linker does not.  Can you send
the complete link line and error message that you get when using gold?
Also include any linker script that may be used.  Thanks.

Ian

Re: [GOLD][PATCH] predefined segment symbol _begin

[Viktor Kutuzov]

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On Wed, 2010-02-10 at 17:16 -0800, Ian Lance Taylor wrote:
> Viktor Kutuzov <vkutuzov@accesssoftek.com> writes:
> 
> > I'm not sure. I have checked the ld scripts, but I didn't find anything
> > related with it. I looked for the _begin definition in the ld sources
> > and I got the same result. It looks strange for me, but anyway.
> > I seen that the _end and _etext symbols were resolved during the build,
> > but _begin wasn't and I added this description accordingly.
> 
> We're going to need to track this down.  I don't want to have gold
> start defining a symbol which the GNU linker does not.  Can you send
> the complete link line and error message that you get when using gold?
> Also include any linker script that may be used.  Thanks.

I have attached the text file with the complete link command line and
error message -- binutils-gold-glibc-link-cmd-line_and_error.txt.

You are right, the _begin symbol is coming from the linker script, but
the used ld script -- ld.so.lds -- is empty. I took one more look on the
build log and I found that the previous step should prepare an
appropriate ld script, which defines  _begin, but, really, doesn't do it
(attached binutils-gold-make-ld-script-cmd-line.txt contains the
complete cmd line). It happens because GOLD doesn't dump the linker
script on -verbose (GNU linker does), which is expected by the sed
script.

I have attached required linker script, which was generated with the gnu
linker for information (ld.so.lds-needed).

So, as result, a real problem is in another place and my patch is
incorrect. Please decline this patch. Sorry for the false alarm.

Thank you.
-Viktor.


[-- Attachment #2: binutils-gold-glibc-link-cmd-line_and_error.txt --]
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arm-none-linux-gnueabi-gcc   -nostdlib -nostartfiles -shared -o /opt/crosstool/build-gold/work/obj.glibc/elf/ld.so			\
		  -Wl,-z,combreloc -Wl,-z,relro -Wl,--hash-style=both -Wl,-z,defs 	\
		  /opt/crosstool/build-gold/work/obj.glibc/elf/librtld.os -Wl,--version-script=/opt/crosstool/build-gold/work/obj.glibc/ld.map		\
		  -Wl,-soname=ld-linux.so.3 -T /opt/crosstool/build-gold/work/obj.glibc/elf/ld.so.lds

/opt/crosstool/build-gold/cross_tool/lib/gcc/arm-none-linux-gnueabi/4.3.4/../../../../arm-none-linux-gnueabi/bin/ld: /opt/crosstool/build-gold/work/obj.glibc/elf/librtld.os: in function _dl_start_final:rtld.c(.text+0x4f8): error: undefined reference to '_begin'
collect2: ld returned 1 exit status

[-- Attachment #3: binutils-gold-make-ld-script-cmd-line.txt --]
[-- Type: text/plain, Size: 364 bytes --]

arm-none-linux-gnueabi-gcc   -nostdlib -nostartfiles -shared 	\
		  -Wl,-z,combreloc -Wl,-z,relro -Wl,--hash-style=both -Wl,-z,defs -Wl,--verbose 2>&1 |	\
		  LC_ALL=C \
		  sed -e '/^=========/,/^=========/!d;/^=========/d'	\
		      -e 's/\. = .* + SIZEOF_HEADERS;/& _begin = . - SIZEOF_HEADERS;/' \
		  > /opt/crosstool/build-gold/work/obj.glibc/elf/ld.so.lds


[-- Attachment #4: ld.so.lds-needed --]
[-- Type: text/x-csrc, Size: 7337 bytes --]

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