To help converted ELF images perform self-relocation, export a symbol
'ElfImageBase' that can be used in the code to discover the start of
the image in memory.

Note the use of PROVIDE() - this ensures that the symbol is only emitted
if a reference to it exists in the code being linked, but no definition.
This means the symbol is never emitted in a way that can conflict with
existing code.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
---
 BaseTools/Scripts/GccBase.lds | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/BaseTools/Scripts/GccBase.lds b/BaseTools/Scripts/GccBase.lds
index a9dd2138d4b5..e73c1206a2e2 100644
--- a/BaseTools/Scripts/GccBase.lds
+++ b/BaseTools/Scripts/GccBase.lds
@@ -12,6 +12,8 @@
 
 SECTIONS {
 
+  PROVIDE(ElfImageBase = .);
+
   /*
    * The PE/COFF binary consists of DOS and PE/COFF headers, and a sequence of
    * section headers adding up to PECOFF_HEADER_SIZE bytes (which differs
-- 
2.26.2


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On 6/8/20 7:34 PM, Ard Biesheuvel wrote:
> To help converted ELF images perform self-relocation, export a symbol
> 'ElfImageBase' that can be used in the code to discover the start of
> the image in memory.
> 
> Note the use of PROVIDE() - this ensures that the symbol is only emitted
> if a reference to it exists in the code being linked, but no definition.
> This means the symbol is never emitted in a way that can conflict with
> existing code.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@arm.com>

Bob, Liming, any objections?

> ---
>   BaseTools/Scripts/GccBase.lds | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/BaseTools/Scripts/GccBase.lds b/BaseTools/Scripts/GccBase.lds
> index a9dd2138d4b5..e73c1206a2e2 100644
> --- a/BaseTools/Scripts/GccBase.lds
> +++ b/BaseTools/Scripts/GccBase.lds
> @@ -12,6 +12,8 @@
>   
>   SECTIONS {
>   
> +  PROVIDE(ElfImageBase = .);
> +
>     /*
>      * The PE/COFF binary consists of DOS and PE/COFF headers, and a sequence of
>      * section headers adding up to PECOFF_HEADER_SIZE bytes (which differs
> 


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Reviewed-by: Bob Feng<bob.c.feng@intel.com>

-----Original Message-----
From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Ard Biesheuvel
Sent: Tuesday, June 9, 2020 1:34 AM
To: devel@edk2.groups.io
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>; Feng, Bob C <bob.c.feng@intel.com>; Gao, Liming <liming.gao@intel.com>; Laszlo Ersek <lersek@redhat.com>; Leif Lindholm <leif@nuviainc.com>; Ilias Apalodimas <ilias.apalodimas@linaro.org>; Julien Grall <julien@xen.org>; Yao, Jiewen <jiewen.yao@intel.com>
Subject: [edk2-devel] [PATCH 2/4] BaseTools/Scripts/GccBase.lds: export image base symbol

To help converted ELF images perform self-relocation, export a symbol 'ElfImageBase' that can be used in the code to discover the start of the image in memory.

Note the use of PROVIDE() - this ensures that the symbol is only emitted if a reference to it exists in the code being linked, but no definition.
This means the symbol is never emitted in a way that can conflict with existing code.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@arm.com>
---
 BaseTools/Scripts/GccBase.lds | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/BaseTools/Scripts/GccBase.lds b/BaseTools/Scripts/GccBase.lds index a9dd2138d4b5..e73c1206a2e2 100644
--- a/BaseTools/Scripts/GccBase.lds
+++ b/BaseTools/Scripts/GccBase.lds
@@ -12,6 +12,8 @@
  SECTIONS { +  PROVIDE(ElfImageBase = .);+   /*    * The PE/COFF binary consists of DOS and PE/COFF headers, and a sequence of    * section headers adding up to PECOFF_HEADER_SIZE bytes (which differs-- 
2.26.2


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