On Thu, Jun 28, 2018 at 5:38 AM Will Deacon <[email protected]> wrote: > > On Wed, Jun 27, 2018 at 12:46:14PM -0700, Greg Hackmann wrote: > > Linking the ARM64 defconfig kernel with LLVM lld fails with the error: > > > > ld.lld: error: unknown argument: -p > > Makefile:1015: recipe for target 'vmlinux' failed > > > > Without this flag, the ARM64 defconfig kernel successfully links with > > lld and boots on Dragonboard 410c.
Ha! Just one single unknown linker flag, to link and boot? That's not too bad. > > After digging through binutils source and changelogs, it turns out that > > -p is only relevant to ancient binutils installations targeting 32-bit > > ARM. binutils accepts -p for AArch64 too, but it's always been > > undocumented and silently ignored. Nothing in the man pages for ld in regards to -p. Seems like it was shortform for "--no-pipeline-knowledge: Stop the linker knowing about the pipeline length". Looks like it was added to binutils via this commit in 1999: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=7ca69e9e10ef290eb3dd62a1e6bebbe4c87fa202 And removed in 2004: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=commit;h=dea514f51da1051f9f3cd7a746e3b68085aa1a72 arch/arm/Makefile has -p as a LD_FLAGS. Is it actually needed there too, or can it be removed from there? I assume we'll want to use lld for arm32 at some point. > > A comment in > > ld/emultempl/aarch64elf.em explains that it's "Only here for backwards > > compatibility". Yep: https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=ld/emultempl/aarch64elf.em;h=edc548f65298e563481bdd9d547fcb9c6b13da04;hb=HEAD#l405 armelf.em also has that comment. Looks like -p has been in arch/arm64/Makefile since the initial commit that added that file. So likely copy+pasted from arch/arm/Makefile. commit 8c2c3df31e3b ("arm64: Build infrastructure"): https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/arch/arm64/Makefile?id=8c2c3df31e3b87cb5348e48776c366ebd1dc5a7a And it looks like arch/arm/Makefile has has -p since the move to git for Linux 2.6: commit 1da177e4c3f4 ("Linux-2.6.12-rc2") https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/arch/arm/Makefile?id=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 So nothing in the kernel commit history to hint at what it was ever used for. As long as you have a version of binutils that not 14 years old, you should be good. Reviewed-by: Nick Desaulniers <[email protected]> -- Thanks, ~Nick Desaulniers
