linux-kernel - [PATCH -fixes] riscv: Fix relocatable kernels with early alternatives using -fno-pie

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Message-Id: <20230526154630.289374-1-alexghiti@rivosinc.com>
Date:   Fri, 26 May 2023 17:46:30 +0200
From:   Alexandre Ghiti <alexghiti@...osinc.com>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Andreas Schwab <schwab@...ux-m68k.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Alexandre Ghiti <alexghiti@...osinc.com>
Subject: [PATCH -fixes] riscv: Fix relocatable kernels with early alternatives using -fno-pie

Early alternatives are called with the mmu disabled, and then should not
access any global symbols through the GOT since it requires relocations,
relocations that we do before but *virtually*. So only use medany code
model for this early code.

Signed-off-by: Alexandre Ghiti <alexghiti@...osinc.com>
---

Note that I'm not very happy with this fix, I think we need to put more
effort into "harmonizing" this very early code (ie before the mmu is
enabled) as it is spread between different locations and compiled
differently. I'll work on that later, but for now, this fix does what is
needed to work (from my testing at least). Any Tested-by on the Unmatched
and T-head boards is welcome!

 arch/riscv/errata/Makefile | 4 ++++
 arch/riscv/kernel/Makefile | 4 ++++
 2 files changed, 8 insertions(+)

diff --git a/arch/riscv/errata/Makefile b/arch/riscv/errata/Makefile
index a1055965fbee..7b2637c8c332 100644
--- a/arch/riscv/errata/Makefile
+++ b/arch/riscv/errata/Makefile
@@ -1,2 +1,6 @@
+ifdef CONFIG_RELOCATABLE
+KBUILD_CFLAGS += -fno-pie
+endif
+
 obj-$(CONFIG_ERRATA_SIFIVE) += sifive/
 obj-$(CONFIG_ERRATA_THEAD) += thead/
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
-- 
2.39.2