Re: allmodconfig builds failing to link on arm64

[Nathan Chancellor <nathan@kernel.org>]

On Fri, Apr 08, 2022 at 05:13:44PM +0100, Will Deacon wrote:
> On Fri, Apr 08, 2022 at 04:06:39PM +0100, Mark Rutland wrote:
> > On Fri, Apr 08, 2022 at 03:45:42PM +0100, Mark Rutland wrote:
> > > On Fri, Apr 08, 2022 at 12:54:07PM +0100, Will Deacon wrote:
> > > > Since -rc1 (although I haven't tried bisecting the merge window), I'm
> > > > not able to link allmodconfig for arm64:
> > > > 
> > > > aarch64-linux-gnu-ld: .init.data has both ordered [`__patchable_function_entries' in init/main.o] and unordered [`.init_array.1' in virt/lib/irqbypass.o] sections
> > > > aarch64-linux-gnu-ld: final link failed: bad value
> > > > make: *** [Makefile:1158: vmlinux] Error 1
> > > > 
> > > > I'm using an Android clang based on 12.0.6 and LD claims to be
> > > > 2.33.1.20191209.
> > > 
> > > I can reproduce that when using the llvm.org 12.0.0 binaries along with the
> > > kernel.org crosstool 9.2.0 binaries (binutils 2.32) to build v5.18-rc1
> > > allmodconfig.
> > > 
> > > I see the failure with (at least) the following combinations that I tested:
> > > 
> > > * LLVM 11.0.0 && binutils 2.34 (kernel.org 8.4.0 binaries)
> > > * LLVM 12.0.0 && binutils 2.30 (kernel.org 8.1.0 binaries)
> > > * LLVM 12.0.0 && binutils 2.32 (kernel.org 9.2.0 binaries)
> > > * LLVM 12.0.0 && binutils 2.34 (kernel.org 8.4.0/9.3.0 binaries)
> > > * LLVM 13.0.0 && binutils 2.34 (kernel.org 8.4.0 binaries)
> > > * LLVM 14.0.0 && binutils 2.34 (kernel.org 8.4.0 binaries)
> > > 
> > > I *DO NOT* see the failure with the following combinations:
> > > 
> > > * LLVM 12.0.0 && binutils 2.36.1 (kernel.org 10.3.0/11.1.0 binaries)
> > > * LLVM 13.0.0 && binutils 2.36.1 (kernel.org 10.3.0/11.1.0 binaries)
> > > * LLVM 14.0.0 && binutils 2.36.1 (kernel.org 10.3.0/11.1.0 binaries)
> > > 
> > > So clearly something changed on the binutils side between 2.34 and
> > > 2.36.1, but I don't know whether either behaviour is incorrect, or
> > > whether LLVM implicitly depends upon a newer binutils version.
> > > 
> > > I don't know why this suddenly became a problem in v5.18-rc1; I'll have
> > > a look.
> > 
> > I also see this with earlier kernel versions, including:
> > 
> > * v5.15 allmodconfig, LLVM 12.0.0, binutils 2.30 (kernel.org 8.1.0 binaries)
> > * v5.16 allmodconfig, LLVM 12.0.0, binutils 2.30 (kernel.org 8.1.0 binaries)
> > * v5.17 allmodconfig, LLVM 12.0.0, binutils 2.30 (kernel.org 8.1.0 binaries)
> > 
> > ... so it doesn't look like this is a (recent) regression.
> 
> Damn, sorry for the mis-diagnosis then. I only just started seeing it, but
> thinking about it I _usually_ build with LLVM=1 which probably rules out
> binutils entirely. For some reason, I ended up in the mixed case today
> and ran into this.
> 
> In any case, it would be good to get it resolved and I'm happy to test out
> any fixes.

I came up with the following diff. I could make the second "depends on"
line a little more readable by splitting it out to two different symbols
such as GCC_SUPPORTS_DYNAMIC_FTRACE_WITH_REGS and
CLANG_SUPPORTS_DYNAMIC_FTRACE_WITH_REGS, which lines up with Linus'
preference here:

https://lore.kernel.org/r/CAHk-=whzW56xChey=k+9KeK_NFxWLfZrt5UWvVjTxYbHLP1Nwg@mail.gmail.com/

That decision is ultimately up to you all though! I can formally send
this along if it looks okay or rework it here depending on feedback.

Cheers,
Nathan

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 57c4c995965f..b2a10846608a 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -175,8 +175,6 @@ config ARM64
 	select HAVE_DEBUG_KMEMLEAK
 	select HAVE_DMA_CONTIGUOUS
 	select HAVE_DYNAMIC_FTRACE
-	select HAVE_DYNAMIC_FTRACE_WITH_REGS \
-		if $(cc-option,-fpatchable-function-entry=2)
 	select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY \
 		if DYNAMIC_FTRACE_WITH_REGS
 	select HAVE_EFFICIENT_UNALIGNED_ACCESS
@@ -228,6 +226,13 @@ config ARM64
 	help
 	  ARM 64-bit (AArch64) Linux support.
 
+config TOOLCHAIN_SUPPORTS_DYNAMIC_FTRACE_WITH_REGS
+	def_bool y
+	depends on $(cc-option,-fpatchable-function-entry=2)
+	# https://github.com/ClangBuiltLinux/linux/issues/1507
+	depends on CC_IS_GCC || (CC_IS_CLANG && LD_IS_LLD) || (CC_IS_CLANG && LD_VERSION >= 23600)
+	select HAVE_DYNAMIC_FTRACE_WITH_REGS
+
 config 64BIT
 	def_bool y
 

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