ARCv3 bare-metal toolchain doesn't support generation of PIE binaries
Closed this issue · 4 comments
abrodkin commented
In U-Boot bootloader for ARC processors we utilize PIE (Position-Independent Executable) binary format to allow U-Boot to re-locate itself from the beginning of the memory space to its very end (effectively to release a precious memory location for something more useful like the Linux kernel).
At the same time since U-Boot for ARC has needed libgcc functions imported in its sources, it doesn't rely on any libraries from the toolchain. Which is nice, because one may use Elf or Linux, big- or little-endian toolchain for building any U-Boot binary for ARC. And that's handy.
But apparently baremetal LD for ARCv3 processors refuses to link PIE binaries, see below. If there's no reason for that except we didn't expect non-Linux PIE binaries to exist, let's remove that artificial constraint.
-
ARCv2 bare-metal
$ arc-elf32-gcc -pie test.c $ arc-elf32-readelf -h a.out ELF Header: Magic: 7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 Class: ELF32 Data: 2's complement, little endian Version: 1 (current) OS/ABI: UNIX - System V ABI Version: 0 Type: DYN (Position-Independent Executable file) Machine: ARCv2 -
ARCv3 bare-metal
ld: -pie not supported:$ arc64-elf-gcc -pie test.c .../bin/../lib/gcc/arc64-snps-elf/12.2.1/../../../../arc64-snps-elf/bin/ld: -pie not supported collect2: error: ld returned 1 exit status -
ARCv3 for Linux - works as expected:
$ arc64-linux-gcc -pie test.c $ arc64-linux-readelf -h a.out ELF Header: Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00 Class: ELF64 Data: 2's complement, little endian Version: 1 (current) OS/ABI: UNIX - System V ABI Version: 0 Type: DYN (Position-Independent Executable file) Machine: Synopsys ARCv3 64-bit processor
abrodkin commented
The following change fixes U-Boot linkage:
diff --git a/arch/arc/config.mk b/arch/arc/config.mk
index 77da6463f8..0c7a377e37 100644
--- a/arch/arc/config.mk
+++ b/arch/arc/config.mk
@@ -21,3 +21,11 @@ PLATFORM_RELFLAGS += -ffunction-sections -fdata-sections -fno-common
# Needed for relocation
LDFLAGS_FINAL += -pie --gc-sections
+
+ifdef CONFIG_CPU_ARCHS5X
+LDFLAGS_FINAL += -marc64linux32
+endif
+
+ifdef CONFIG_CPU_ARCHS6X
+LDFLAGS_FINAL += -marc64linux64
+endifabrodkin commented
@claziss it's interesting - Elf toolchain for ARCv3 (arc64-elf) doesn't support arc64linux32 emulation:
$ arc64-elf-ld --help | grep "supported emulations"
arc64-elf-ld: supported emulations: arc64elf64 arc64elf32 arc64linux64
while Linux toolchain (arc64-linux) does support it:
$ arc64-linux-ld --help | grep "supported emulations"
arc64-linux-ld: supported emulations: arc64linux64 arc64elf64 arc64elf32 arc64linux32
Which makes pre-built Elf toolchain for ARCv3 still not capable of building U-Boot, as well as the loader with Linux kernel for ARC HS58 if it's linked to 0 but not 0x8z (as in olde good days of ARCompact & ARCv2).
claziss commented
The default emulation for ARCv3 elf targets doesn't support PIE as it doesn't make too much sense, but one can use the linux emulations (as shown in a previous message) with a custom linker script, for example:
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claziss commented
Missing emulation fixed here: foss-for-synopsys-dwc-arc-processors/binutils-gdb@acce4ba