[Clang][Driver] riscv64-elf target does not recognise -pie link time argument

[mintsuki]

As per title, trying to link an executable using the clang driver, using a riscv64-elf target, results in the following warning:

clang: warning: argument unused during compilation: '-pie' [-Wunused-command-line-argument]

The -pie flag (and other possibly necessary flags for PIE linkage) are not passed to the linker.

[mintsuki]

This also applies to riscv32, and may affect more architectures/targets, as I haven't tested beyond this.

[llvmbot]

@llvm/issue-subscribers-backend-risc-v

Author: None (mintsuki)

As per title, trying to link an executable using the `clang` driver, using a `riscv64-elf` target, results in the following warning: ``` clang: warning: argument unused during compilation: '-pie' [-Wunused-command-line-argument] ```

The -pie flag (and other possibly necessary flags for PIE linkage) are not passed to the linker.

[llvmbot]

@llvm/issue-subscribers-clang-driver

Author: None (mintsuki)

As per title, trying to link an executable using the `clang` driver, using a `riscv64-elf` target, results in the following warning: ``` clang: warning: argument unused during compilation: '-pie' [-Wunused-command-line-argument] ```

The -pie flag (and other possibly necessary flags for PIE linkage) are not passed to the linker.

[lenary]

Are you trying to make a baremetal executable, or a linux executable?

riscv64-elf and riscv32-elf are shorthands for riscv64-unknown-unknown-elf, which is the baremetal triple. There is work on supporting static PIE with this toolchain, but that needs a custom-written loader.

More likely you're compiling for linux, so use riscv64-unknown-linux or riscv32-unknown-linux which will support -pie.

[mintsuki]

I am compiling for bare metal. Calling the linker directly, or using a -linux target to fool the Clang driver into passing -pie and friends to the linker works perfectly fine for my use case.

[mintsuki]

Also worth noting that there are other baremetal targets for which -pie is a recognised argument, and works as expected, such as loongarch64-elf, and x86_64-elf.

EDIT: Though on further looking into it, that seems to be because the driver calls into GCC for linking (and imo it shouldn't) for these targets. See my other opened issue #149850.

[jrtc27]

It also works fine if you pass it through manually to LLD via -Wl,-pie (as done by OpenSBI if it detects support). Bare-metal (static) PIEs aren't that weird; in the case of OpenSBI it just self-relocates at startup.

[mintsuki]

Yeah, I have been using -Wl,-pie as a workaround for now (or just calling the linker directly), but I don't see why not support -pie. GCC also supports it fine.

[lenary]

#147589 is adding -static-pie support to the baremetal toolchain which aarch64 and riscv use.

[mintsuki]

#147589 is adding -static-pie support to the baremetal toolchain which aarch64 and riscv use.

I guess that works, too. Thank you very much!