linux-kernel - [PATCH v4 3/6] riscv: Move global pointer loading to a macro

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Message-ID: <20230927224757.1154247-11-samitolvanen@google.com>
Date:   Wed, 27 Sep 2023 22:48:01 +0000
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Kees Cook <keescook@...omium.org>
Cc:     Clement Leger <cleger@...osinc.com>, Guo Ren <guoren@...nel.org>,
        Deepak Gupta <debug@...osinc.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Fangrui Song <maskray@...gle.com>,
        linux-riscv@...ts.infradead.org, llvm@...ts.linux.dev,
        linux-kernel@...r.kernel.org,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH v4 3/6] riscv: Move global pointer loading to a macro

In Clang 17, -fsanitize=shadow-call-stack uses the newly declared
platform register gp for storing shadow call stack pointers. As
this is obviously incompatible with gp relaxation, in preparation
for CONFIG_SHADOW_CALL_STACK support, move global pointer loading
to a single macro, which we can cleanly disable when SCS is used
instead.

Link: https://reviews.llvm.org/rGaa1d2693c256
Link: https://github.com/riscv-non-isa/riscv-elf-psabi-doc/commit/a484e843e6eeb51f0cb7b8819e50da6d2444d769
Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
Tested-by: Nathan Chancellor <nathan@...nel.org>
---
 arch/riscv/include/asm/asm.h      |  8 ++++++++
 arch/riscv/kernel/entry.S         |  6 ++----
 arch/riscv/kernel/head.S          | 15 +++------------
 arch/riscv/kernel/suspend_entry.S |  5 +----
 4 files changed, 14 insertions(+), 20 deletions(-)

diff --git a/arch/riscv/include/asm/asm.h b/arch/riscv/include/asm/asm.h
index 8e446be2d57c..f34dd1a526a1 100644
--- a/arch/riscv/include/asm/asm.h
+++ b/arch/riscv/include/asm/asm.h
@@ -109,6 +109,14 @@
 	REG_L \dst, 0(\dst)
 .endm
 
+/* load __global_pointer to gp */
+.macro load_global_pointer
+.option push
+.option norelax
+	la gp, __global_pointer$
+.option pop
+.endm
+
 	/* save all GPs except x1 ~ x5 */
 	.macro save_from_x6_to_x31
 	REG_S x6,  PT_T1(sp)
diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index a306562636e4..6215dcf2e83b 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -75,10 +75,8 @@ _save_context:
 	csrw CSR_SCRATCH, x0
 
 	/* Load the global pointer */
-.option push
-.option norelax
-	la gp, __global_pointer$
-.option pop
+	load_global_pointer
+
 	move a0, sp /* pt_regs */
 	la ra, ret_from_exception
 
diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
index 3710ea5d160f..a0484d95d8fb 100644
--- a/arch/riscv/kernel/head.S
+++ b/arch/riscv/kernel/head.S
@@ -110,10 +110,7 @@ relocate_enable_mmu:
 	csrw CSR_TVEC, a0
 
 	/* Reload the global pointer */
-.option push
-.option norelax
-	la gp, __global_pointer$
-.option pop
+	load_global_pointer
 
 	/*
 	 * Switch to kernel page tables.  A full fence is necessary in order to
@@ -134,10 +131,7 @@ secondary_start_sbi:
 	csrw CSR_IP, zero
 
 	/* Load the global pointer */
-	.option push
-	.option norelax
-		la gp, __global_pointer$
-	.option pop
+	load_global_pointer
 
 	/*
 	 * Disable FPU & VECTOR to detect illegal usage of
@@ -228,10 +222,7 @@ pmp_done:
 #endif /* CONFIG_RISCV_M_MODE */
 
 	/* Load the global pointer */
-.option push
-.option norelax
-	la gp, __global_pointer$
-.option pop
+	load_global_pointer
 
 	/*
 	 * Disable FPU & VECTOR to detect illegal usage of
diff --git a/arch/riscv/kernel/suspend_entry.S b/arch/riscv/kernel/suspend_entry.S
index f7960c7c5f9e..d5cf8b575777 100644
--- a/arch/riscv/kernel/suspend_entry.S
+++ b/arch/riscv/kernel/suspend_entry.S
@@ -61,10 +61,7 @@ END(__cpu_suspend_enter)
 
 SYM_TYPED_FUNC_START(__cpu_resume_enter)
 	/* Load the global pointer */
-	.option push
-	.option norelax
-		la gp, __global_pointer$
-	.option pop
+	load_global_pointer
 
 #ifdef CONFIG_MMU
 	/* Save A0 and A1 */
-- 
2.42.0.515.g380fc7ccd1-goog