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The default behavior of the GCC compiler is to emit uninitialized globals
with external linkage into a COMMON section, where duplicate definitions
are merged. This may result in unexpected behavior, since global variables
defined under the same name in different C files may not refer to the same
logical data item.
For instance, the definitions of EFI_EVENT mVirtualAddressChangeEvent that
[used to] appear in the following files:
CryptoPkg/Library/BaseCryptLib/SysCall/RuntimeMemAllocation.c
MdeModulePkg/Universal/Variable/RuntimeDxe/VariableDxe.c
will be folded into a single instance of the variable when the latter
module includes the former library, which can lead to unexpected results.
Even if some may argue that there are legal uses for COMMON allocation, the
high modularity of EDK2 combined with the low level of awareness of the
intracicies surrounding common allocation and the generally poor EDK2
developer discipline regarding the use of the STATIC keyword* make a strong
case for disabling it by default, and re-enabling it explicitly for packages
that depend on it.
So prevent GCC from emitting variables into the COMMON section, by passing
-fno-common to the compiler, and discarding the section in the GNU ld linker
script.
* Any function or variable that is only referenced from the translation unit
that defines it could be made STATIC. This does not only prevent issues
like the above, it also allows the compiler to generate better code, e.g.,
drop out of line function definitions after inlining all invocations or
perform constant propagation on variables.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Liming Gao <liming.gao@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Laszlo Ersek <lersek@redhat.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19164 6f19259b-4bc3-4df7-8a09-765794883524
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All AutoGen.obj files consist of global GUID definitions, fixed
and patchable PCDs and other data that is essentially read-only at
runtime but has not been declared as such for various reasons.
By moving these contents to .text we achieve two things:
- global GUIDs and other data items which must be constant for correct
program operation can no longer be modified, for instance, when
running a DXE_RUNTIME_MODULE binary under the OS with the Properties
Table feature for memory protection enabled;
- the .data section becomes smaller, and may be dropped completely for
many XIP modules, which reduces wasted FV space if the PE/COFF section
alignment is large.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Tested-by: Liming Gao <liming.gao@intel.com>
Tested-by: Leif Lindholm <leif.lindholm@linaro.org>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18137 6f19259b-4bc3-4df7-8a09-765794883524
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Now that GenFw honors the ELF section alignment when placing the
PE/COFF sections in the output, the start of the PE/COFF version of
.data will be aligned to the alignment of .text if its alignment is
higher than the default. So duplicate this behavior in the ELF output,
this will make the memory layout of the PE/COFF binary match the
layout of the ELF version more closely.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Tested-by: Liming Gao <liming.gao@intel.com>
Tested-by: Leif Lindholm <leif.lindholm@linaro.org>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18136 6f19259b-4bc3-4df7-8a09-765794883524
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This unifies all GCC linker scripts into a single parametrised GCC
linker script that can be used for all GCC versions and architectures.
The two parameters that can be set on the linker command line are:
- PECOFF_HEADER_SIZE, this is a build time property of GenFw, but
its value is different between 32-bit and 64-bit;
- common-page-size, this can be set using -z on the ld command line,
and controls the value of the COMMONPAGESIZE constant when used in
a linker script. This value is used for the minimum section alignment.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Tested-by: Liming Gao <liming.gao@intel.com>
Tested-by: Leif Lindholm <leif.lindholm@linaro.org>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18135 6f19259b-4bc3-4df7-8a09-765794883524
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