Revision: 19164
http://sourceforge.net/p/edk2/code/19164
Author: abiesheuvel
Date: 2015-12-08 07:40:12 +0000 (Tue, 08 Dec 2015)
Log Message:
-----------
BaseTools GCC: avoid the use of COMMON symbols
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 <[email protected]>
Reviewed-by: Liming Gao <[email protected]>
Reviewed-by: Laszlo Ersek <[email protected]>
Tested-by: Laszlo Ersek <[email protected]>
Modified Paths:
--------------
trunk/edk2/BaseTools/Conf/tools_def.template
trunk/edk2/BaseTools/Scripts/GccBase.lds
Modified: trunk/edk2/BaseTools/Conf/tools_def.template
===================================================================
--- trunk/edk2/BaseTools/Conf/tools_def.template 2015-12-08 07:35:30 UTC
(rev 19163)
+++ trunk/edk2/BaseTools/Conf/tools_def.template 2015-12-08 07:40:12 UTC
(rev 19164)
@@ -4318,7 +4318,7 @@
DEBUG_*_*_OBJCOPY_ADDDEBUGFLAG =
--add-gnu-debuglink=$(DEBUG_DIR)/$(MODULE_NAME).debug
RELEASE_*_*_OBJCOPY_ADDDEBUGFLAG =
-DEFINE GCC_ALL_CC_FLAGS = -g -Os -fshort-wchar -fno-strict-aliasing
-Wall -Werror -Wno-array-bounds -c -include AutoGen.h
+DEFINE GCC_ALL_CC_FLAGS = -g -Os -fshort-wchar -fno-strict-aliasing
-Wall -Werror -Wno-array-bounds -c -include AutoGen.h -fno-common
DEFINE GCC_IA32_CC_FLAGS = DEF(GCC_ALL_CC_FLAGS) -m32 -malign-double
-freorder-blocks -freorder-blocks-and-partition -O2 -mno-stack-arg-probe
DEFINE GCC_X64_CC_FLAGS = DEF(GCC_ALL_CC_FLAGS) -mno-red-zone
-Wno-address -mno-stack-arg-probe
DEFINE GCC_IPF_CC_FLAGS = DEF(GCC_ALL_CC_FLAGS)
-minline-int-divide-min-latency
@@ -4349,7 +4349,7 @@
DEFINE GCC_ARM_RC_FLAGS = -I binary -O elf32-littlearm -B arm
--rename-section .data=.hii
DEFINE GCC_AARCH64_RC_FLAGS = -I binary -O elf64-littleaarch64 -B
aarch64 --rename-section .data=.hii
-DEFINE GCC44_ALL_CC_FLAGS = -g -fshort-wchar -fno-strict-aliasing
-Wall -Werror -Wno-array-bounds -ffunction-sections -fdata-sections -c -include
AutoGen.h -DSTRING_ARRAY_NAME=$(BASE_NAME)Strings
+DEFINE GCC44_ALL_CC_FLAGS = -g -fshort-wchar -fno-strict-aliasing
-Wall -Werror -Wno-array-bounds -ffunction-sections -fdata-sections -c -include
AutoGen.h -fno-common -DSTRING_ARRAY_NAME=$(BASE_NAME)Strings
DEFINE GCC44_IA32_CC_FLAGS = DEF(GCC44_ALL_CC_FLAGS) -m32
-malign-double -fno-stack-protector -D EFI32 -fno-asynchronous-unwind-tables
DEFINE GCC44_X64_CC_FLAGS = DEF(GCC44_ALL_CC_FLAGS) -m64
-fno-stack-protector "-DEFIAPI=__attribute__((ms_abi))" -DNO_BUILTIN_VA_FUNCS
-mno-red-zone -Wno-address -mcmodel=large -fno-asynchronous-unwind-tables
DEFINE GCC44_IA32_X64_DLINK_COMMON = -nostdlib -n -q --gc-sections -z
common-page-size=0x20
Modified: trunk/edk2/BaseTools/Scripts/GccBase.lds
===================================================================
--- trunk/edk2/BaseTools/Scripts/GccBase.lds 2015-12-08 07:35:30 UTC (rev
19163)
+++ trunk/edk2/BaseTools/Scripts/GccBase.lds 2015-12-08 07:40:12 UTC (rev
19164)
@@ -46,7 +46,7 @@
*/
.data ALIGN(ALIGNOF(.text)) : ALIGN(CONSTANT(COMMONPAGESIZE)) {
*(.data .data.* .gnu.linkonce.d.*)
- *(.bss .bss.* *COM*)
+ *(.bss .bss.*)
}
.eh_frame ALIGN(CONSTANT(COMMONPAGESIZE)) : {
@@ -66,5 +66,6 @@
*(.dynamic)
*(.hash)
*(.comment)
+ *(COMMON)
}
}
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