Re: [PATCH v8 1/3] riscv: Introduce CONFIG_RELOCATABLE

On 19/05/2023 23:55, Palmer Dabbelt wrote:

On Fri, 19 May 2023 14:48:59 PDT (-0700), schwab@linux-m68k.org wrote:

quoted

On Mai 19 2023, Alexandre Ghiti wrote:

quoted

I have tested the following patch successfully, can you give it a try
while I make sure this is the only place I forgot to add the -fno-pie
flag?

diff --git a/arch/riscv/kernel/Makefile b/arch/riscv/kernel/Makefile
index fbdccc21418a..153864e4f399 100644
--- a/arch/riscv/kernel/Makefile
+++ b/arch/riscv/kernel/Makefile

@@ -23,6 +23,10 @@ ifdef CONFIG_FTRACE

 CFLAGS_REMOVE_alternative.o = $(CC_FLAGS_FTRACE)
 CFLAGS_REMOVE_cpufeature.o = $(CC_FLAGS_FTRACE)
 endif
+ifdef CONFIG_RELOCATABLE
+CFLAGS_alternative.o += -fno-pie
+CFLAGS_cpufeature.o += -fno-pie
+endif
 ifdef CONFIG_KASAN
 KASAN_SANITIZE_alternative.o := n
 KASAN_SANITIZE_cpufeature.o := n

I can confirm that this fixes the crash.

Thanks.  Alex: can you send a patch?

I don't think this patch alone will work, all the code in early 
alternatives must be compiled with -fno-pie, but I'm a bit scared that's 
a "big" constraint. For now, I see 2 solutions:

- Document somewhere the fact that anything called from early 
alternatives must be compiled with -fno-pie
- Or relocate once with physical address, call early alternatives, and 
then do the final virtual relocation

Both options can be cumbersome in their own way, if anyone has an 
opinion, I'd be happy to discuss that :)