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From: Bo Gan <ganboing@gmail.com>
To: opensbi@lists.infradead.org
Subject: [PATCH] include: riscv_asm: Optimize csr_xyz() macros to reduce stack usage
Date: Mon, 15 Dec 2025 21:25:28 -0800	[thread overview]
Message-ID: <20251216052528.18896-1-ganboing@gmail.com> (raw)

When using debug builds, aka., DEBUG=1, csr_write_num() function can
trigger stack overflow. This is caused by the large amount of macro
expansion of csr_write(...), which, under debug builds, will generate
massive amount of stack variables (tested with GCC 13.2.0). The issue
is masked previously as we didn't have too many csr_write()'s before
commit 55296fd27c0c, but now, it does overflow the default 4KB stack.

The csr_read(relaxed) macros already use the "register" modifier to
optimize stack usage (perhaps unknowingly?), so this patch just
follows suit.

Fixes: 55296fd27c0c ("lib: Allow custom CSRs in csr_read_num() and csr_write_num()")
Signed-off-by: Bo Gan <ganboing@gmail.com>
---
 include/sbi/riscv_asm.h | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/sbi/riscv_asm.h b/include/sbi/riscv_asm.h
index ef48dc89..0cf3fc37 100644
--- a/include/sbi/riscv_asm.h
+++ b/include/sbi/riscv_asm.h
@@ -83,7 +83,7 @@
 
 #define csr_swap(csr, val)                                              \
 	({                                                              \
-		unsigned long __v = (unsigned long)(val);               \
+		register unsigned long __v = (unsigned long)(val);      \
 		__asm__ __volatile__("csrrw %0, " __ASM_STR(csr) ", %1" \
 				     : "=r"(__v)                        \
 				     : "rK"(__v)                        \
@@ -111,7 +111,7 @@
 
 #define csr_write(csr, val)                                        \
 	({                                                         \
-		unsigned long __v = (unsigned long)(val);          \
+		register unsigned long __v = (unsigned long)(val); \
 		__asm__ __volatile__("csrw " __ASM_STR(csr) ", %0" \
 				     :                             \
 				     : "rK"(__v)                   \
@@ -120,7 +120,7 @@
 
 #define csr_read_set(csr, val)                                          \
 	({                                                              \
-		unsigned long __v = (unsigned long)(val);               \
+		register unsigned long __v = (unsigned long)(val);      \
 		__asm__ __volatile__("csrrs %0, " __ASM_STR(csr) ", %1" \
 				     : "=r"(__v)                        \
 				     : "rK"(__v)                        \
@@ -130,7 +130,7 @@
 
 #define csr_set(csr, val)                                          \
 	({                                                         \
-		unsigned long __v = (unsigned long)(val);          \
+		register unsigned long __v = (unsigned long)(val); \
 		__asm__ __volatile__("csrs " __ASM_STR(csr) ", %0" \
 				     :                             \
 				     : "rK"(__v)                   \
@@ -139,7 +139,7 @@
 
 #define csr_read_clear(csr, val)                                        \
 	({                                                              \
-		unsigned long __v = (unsigned long)(val);               \
+		register unsigned long __v = (unsigned long)(val);      \
 		__asm__ __volatile__("csrrc %0, " __ASM_STR(csr) ", %1" \
 				     : "=r"(__v)                        \
 				     : "rK"(__v)                        \
@@ -149,7 +149,7 @@
 
 #define csr_clear(csr, val)                                        \
 	({                                                         \
-		unsigned long __v = (unsigned long)(val);          \
+		register unsigned long __v = (unsigned long)(val); \
 		__asm__ __volatile__("csrc " __ASM_STR(csr) ", %0" \
 				     :                             \
 				     : "rK"(__v)                   \
-- 
2.34.1


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             reply	other threads:[~2025-12-16  5:27 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-12-16  5:25 Bo Gan [this message]
2025-12-27  9:09 ` [PATCH] include: riscv_asm: Optimize csr_xyz() macros to reduce stack usage Anup Patel

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