BaseTools/GCC AARCH64: force disable PIC code generation

As a security measure, some distro toolchains now default to PIC code
generation, allowing executables (as opposed to shared libraries) using
the objects to be built as PIE binaries, which can be loaded at a random
virtual offset.

However, our ELF to PE/COFF generation code does not deal with the
resulting relocation types (i.e., GOT based), and so the use of PIC code
leads to GenFw errors.

Given that
a) our non-PIC PE/COFF executables are already relocatable,
b) PIC code leads to all symbol references to be indirected via GOT
   entries containing absolute addresses, each requiring an entry in the
   relocation table,
c) the AArch64 ISA makes it perfectly feasible to built PIE executables
   from non-PIC code,

there is absolutely no upside to using PIC code for building EDK2 modules,
and so we're better off simply disabling it unconditionally.

Note that when running under the OS, the GOT has an additional advantage,
i.e., that all .text/.rodata pages remain clean and so can be shared between
processes. This does not apply to the UEFI environment, however.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Laszlo Ersek <lersek@redhat.com>

diff --git a/BaseTools/Conf/tools_def.template b/BaseTools/Conf/tools_def.template
index 0aabdeb2d973e12f6e6b9c5bd53e170bb7644e37..2c5cd58089121d71dbd59fd16a786aeb82fbf442 100755 (executable)
--- a/BaseTools/Conf/tools_def.template
+++ b/BaseTools/Conf/tools_def.template
@@ -4341,7 +4341,7 @@ DEFINE GCC_X64_CC_FLAGS            = DEF(GCC_ALL_CC_FLAGS) -mno-red-zone -Wno-ad
 DEFINE GCC_IPF_CC_FLAGS            = DEF(GCC_ALL_CC_FLAGS) -minline-int-divide-min-latency\r
 DEFINE GCC_ARM_CC_FLAGS            = DEF(GCC_ALL_CC_FLAGS) -mlittle-endian -mabi=aapcs -fno-short-enums -funsigned-char -ffunction-sections -fdata-sections -fomit-frame-pointer -fno-builtin -Wno-address -mthumb -mfloat-abi=soft\r
 DEFINE GCC_ARM_CC_XIPFLAGS         = -mno-unaligned-access\r
-DEFINE GCC_AARCH64_CC_FLAGS        = DEF(GCC_ALL_CC_FLAGS) -mlittle-endian -fno-short-enums -fverbose-asm -funsigned-char  -ffunction-sections -fdata-sections -fno-builtin -Wno-address -fno-asynchronous-unwind-tables\r
+DEFINE GCC_AARCH64_CC_FLAGS        = DEF(GCC_ALL_CC_FLAGS) -mlittle-endian -fno-short-enums -fverbose-asm -funsigned-char  -ffunction-sections -fdata-sections -fno-builtin -Wno-address -fno-asynchronous-unwind-tables -fno-pic\r
 DEFINE GCC_AARCH64_CC_XIPFLAGS     = -mstrict-align\r
 DEFINE GCC_DLINK_FLAGS_COMMON      = -nostdlib --pie\r
 DEFINE GCC_DLINK2_FLAGS_COMMON     = -Wl,--script=$(EDK_TOOLS_PATH)/Scripts/GccBase.lds\r