linux-kernel - [RFC PATCH 2/4] riscv: add compile-time test into is_compat

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Message-ID: <20231222074605.452452-3-leobras@redhat.com>
Date: Fri, 22 Dec 2023 04:46:02 -0300
From: Leonardo Bras <leobras@...hat.com>
To: Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Eric Biederman <ebiederm@...ssion.com>,
	Kees Cook <keescook@...omium.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Leonardo Bras <leobras@...hat.com>,
	Conor Dooley <conor.dooley@...rochip.com>,
	Andy Chiu <andy.chiu@...ive.com>,
	Greg Ungerer <gerg@...nel.org>,
	Vincent Chen <vincent.chen@...ive.com>,
	Xiao Wang <xiao.w.wang@...el.com>,
	Charlie Jenkins <charlie@...osinc.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Alexandre Ghiti <alexghiti@...osinc.com>,
	Kemeng Shi <shikemeng@...weicloud.com>,
	David Hildenbrand <david@...hat.com>,
	"Matthew Wilcox (Oracle)" <willy@...radead.org>,
	Qinglin Pan <panqinglin2020@...as.ac.cn>,
	Greentime Hu <greentime.hu@...ive.com>,
	Björn Töpel <bjorn@...osinc.com>,
	Clément Léger <cleger@...osinc.com>,
	Guo Ren <guoren@...nel.org>
Cc: linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: [RFC PATCH 2/4] riscv: add compile-time test into is_compat_task()

Currently several places will test for CONFIG_COMPAT before testing
is_compat_task(), probably in order to avoid a run-time test into the task
structure.

Since is_compat_task() is an inlined function, it would be helpful to add a
compile-time test of CONFIG_COMPAT, making sure it always returns zero when
the option is not enabled during the kernel build.

With this, the compiler is able to understand in build-time that
is_compat_task() will always return 0, and optimize-out some of the extra
code introduced by the option.

This will also allow removing a lot #ifdefs that were introduced, and make
the code more clean.

Signed-off-by: Leonardo Bras <leobras@...hat.com>
---
 arch/riscv/include/asm/compat.h    | 3 +++
 arch/riscv/include/asm/elf.h       | 4 ----
 arch/riscv/include/asm/pgtable.h   | 6 ------
 arch/riscv/include/asm/processor.h | 4 ++--
 4 files changed, 5 insertions(+), 12 deletions(-)

diff --git a/arch/riscv/include/asm/compat.h b/arch/riscv/include/asm/compat.h
index 2ac955b51148f..91517b51b8e27 100644
--- a/arch/riscv/include/asm/compat.h
+++ b/arch/riscv/include/asm/compat.h
@@ -14,6 +14,9 @@
 
 static inline int is_compat_task(void)
 {
+	if (!IS_ENABLED(CONFIG_COMPAT))
+		return 0;
+
 	return test_thread_flag(TIF_32BIT);
 }
 
diff --git a/arch/riscv/include/asm/elf.h b/arch/riscv/include/asm/elf.h
index 59a08367fddd7..2e88257cafaea 100644
--- a/arch/riscv/include/asm/elf.h
+++ b/arch/riscv/include/asm/elf.h
@@ -53,13 +53,9 @@ extern bool compat_elf_check_arch(Elf32_Ehdr *hdr);
 #define ELF_ET_DYN_BASE		((DEFAULT_MAP_WINDOW / 3) * 2)
 
 #ifdef CONFIG_64BIT
-#ifdef CONFIG_COMPAT
 #define STACK_RND_MASK		(is_compat_task() ? \
 				 0x7ff >> (PAGE_SHIFT - 12) : \
 				 0x3ffff >> (PAGE_SHIFT - 12))
-#else
-#define STACK_RND_MASK		(0x3ffff >> (PAGE_SHIFT - 12))
-#endif
 #endif
 
 /*
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 1d472b31e0cfe..ea5b269be223a 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -127,16 +127,10 @@
 #define VA_USER_SV48 (UL(1) << (VA_BITS_SV48 - 1))
 #define VA_USER_SV57 (UL(1) << (VA_BITS_SV57 - 1))
 
-#ifdef CONFIG_COMPAT
 #define MMAP_VA_BITS_64 ((VA_BITS >= VA_BITS_SV48) ? VA_BITS_SV48 : VA_BITS)
 #define MMAP_MIN_VA_BITS_64 (VA_BITS_SV39)
 #define MMAP_VA_BITS (is_compat_task() ? VA_BITS_SV32 : MMAP_VA_BITS_64)
 #define MMAP_MIN_VA_BITS (is_compat_task() ? VA_BITS_SV32 : MMAP_MIN_VA_BITS_64)
-#else
-#define MMAP_VA_BITS ((VA_BITS >= VA_BITS_SV48) ? VA_BITS_SV48 : VA_BITS)
-#define MMAP_MIN_VA_BITS (VA_BITS_SV39)
-#endif /* CONFIG_COMPAT */
-
 #else
 #include <asm/pgtable-32.h>
 #endif /* CONFIG_64BIT */
diff --git a/arch/riscv/include/asm/processor.h b/arch/riscv/include/asm/processor.h
index f19f861cda549..ed32e53e55999 100644
--- a/arch/riscv/include/asm/processor.h
+++ b/arch/riscv/include/asm/processor.h
@@ -22,7 +22,7 @@
 ({								\
 	unsigned long mmap_end;					\
 	typeof(addr) _addr = (addr);				\
-	if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) && is_compat_task())) \
+	if ((_addr) == 0 || is_compat_task())			\
 		mmap_end = STACK_TOP_MAX;			\
 	else if ((_addr) >= VA_USER_SV57)			\
 		mmap_end = STACK_TOP_MAX;			\
@@ -39,7 +39,7 @@
 	typeof(addr) _addr = (addr);				\
 	typeof(base) _base = (base);				\
 	unsigned long rnd_gap = DEFAULT_MAP_WINDOW - (_base);	\
-	if ((_addr) == 0 || (IS_ENABLED(CONFIG_COMPAT) && is_compat_task())) \
+	if ((_addr) == 0 || is_compat_task())			\
 		mmap_base = (_base);				\
 	else if (((_addr) >= VA_USER_SV57) && (VA_BITS >= VA_BITS_SV57)) \
 		mmap_base = VA_USER_SV57 - rnd_gap;		\
-- 
2.43.0