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@redhat.com>
Reviewed-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Andy Chiu <andy.chiu@sifive.com>
Link: https://lore.kernel.org/r/20240103160024.70305-5-leobras@redhat.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

Author: Leonardo Bras

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);
 }
 

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
 
 /*

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 */

arch/riscv/include/asm/processor.h

@@ -28,7 +28,7 @@
 ({								\
 	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) && (VA_BITS >= VA_BITS_SV57)) \
 		mmap_end = VA_USER_SV57;			\
@@ -45,7 +45,7 @@
 	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;		\