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| author | Alex Richardson <alexrichardson@google.com> | 2021-12-09 04:05:29 -0800 |
|---|---|---|
| committer | Alex Richardson <alexrichardson@google.com> | 2023-06-08 07:08:49 -0700 |
| commit | bf6ab93088f7efe7c66f88b71d87b09893ee32e3 (patch) | |
| tree | 88e03b8b2ca2180af0060bd06c07ce438ccdac38 | |
| parent | 69111c40f5fbde5ffcdcc1a3ba84789a04f260e1 (diff) | |
| download | lk-bf6ab93088f7efe7c66f88b71d87b09893ee32e3.tar.gz | |
[riscv] Workaround for undef-weak symbol relocations with clang+lld
When building with clang -mcmodel=medany and linking with ld.lld, we get
out-of-range relocation errors for undefined __start_<section> symbols
since 0 cannot be represented as a PC-relative offset). This is not a
problem with ld.bfd since ld.bfd rewrites the instructions to avoid the
out-of-range PC-relative relocation. For now, the simplest workaround is
to build with -fpie -mcmodel=medany (thus indirecting these symbols via
the GOT). This will be done automatically once clang includes
https://reviews.llvm.org/D107280.
Without this change I get the following linker errors:
ld.lld: error: dev/driver.c:21:(.text+0x1E): relocation R_RISCV_PCREL_HI20 out of range: -524295 is not in [-524288, 524287]; references __start_devices
See https://github.com/riscv-non-isa/riscv-elf-psabi-doc/issues/126 and
https://github.com/riscv-non-isa/riscv-elf-psabi-doc/pull/201.
| -rw-r--r-- | engine.mk | 12 |
1 files changed, 12 insertions, 0 deletions
@@ -224,6 +224,18 @@ ifeq ($(ARCH),riscv) # TODO: This is no longer true as of LLVM 15, so should add a version check ifeq ($(LINKER_TYPE),lld) ARCH_COMPILEFLAGS += -mno-relax +# Work around out-of-range undef-weak relocations when building with clang and +# linking with ld.lld. This is not a problem with ld.bfd since ld.bfd rewrites +# the instructions to avoid the out-of-range PC-relative relocation +# See https://github.com/riscv-non-isa/riscv-elf-psabi-doc/issues/126 for more +# details. For now, the simplest workaround is to build with -fpie when using +# a version of clang that does not include https://reviews.llvm.org/D107280. +# TODO: Add a clang 17 version check now that the review has been merged. +ifeq ($(COMPILER_TYPE),clang) +# We also add the -fdirect-access-external-data flag is added to avoid the +# majority of the performance overhead caused by -fPIE. +ARCH_COMPILEFLAGS += -fPIE -fdirect-access-external-data +endif endif endif |