[PATCH 2/3] riscv: alternative: Use the statically extracted vDSO section offsets

[Thomas Weißschuh]

Currently the alternative sections are extracted from the vDSO
binaries at runtime. This has runtime overhead and also doesn't
work for the compat vDSO.

Use the offsets generated during the build instead, fixing both issues.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>
---
 arch/riscv/kernel/alternative.c | 28 +++++++++++-----------------
 1 file changed, 11 insertions(+), 17 deletions(-)

diff --git a/arch/riscv/kernel/alternative.c b/arch/riscv/kernel/alternative.c
index 104dc0862c5c..6aba169fb213 100644
--- a/arch/riscv/kernel/alternative.c
+++ b/arch/riscv/kernel/alternative.c
@@ -173,24 +173,14 @@ static void __init_or_module _apply_alternatives(struct alt_entry *begin,
 				stage);
 }
 
-static void __init apply_vdso_alternatives(void *start)
+static __always_inline
+void __init apply_vdso_alternatives(void *base, size_t alternatives_begin, size_t alternatives_end)
 {
-	const Elf_Ehdr *hdr;
-	const Elf_Shdr *shdr;
-	const Elf_Shdr *alt;
-	struct alt_entry *begin, *end;
-
-	hdr = (Elf_Ehdr *)start;
-	shdr = (void *)hdr + hdr->e_shoff;
-	alt = find_section(hdr, shdr, ".alternative");
-	if (!alt)
+	if (alternatives_begin == alternatives_end)
 		return;
 
-	begin = (void *)hdr + alt->sh_offset,
-	end = (void *)hdr + alt->sh_offset + alt->sh_size,
-
-	_apply_alternatives((struct alt_entry *)begin,
-			    (struct alt_entry *)end,
+	_apply_alternatives(base + alternatives_begin,
+			    base + alternatives_end,
 			    RISCV_ALTERNATIVES_BOOT);
 }
 
@@ -204,10 +194,14 @@ void __init apply_boot_alternatives(void)
 			    RISCV_ALTERNATIVES_BOOT);
 
 	if (IS_ENABLED(CONFIG_MMU))
-		apply_vdso_alternatives(vdso_start);
+		apply_vdso_alternatives(vdso_start,
+					__vdso_alternatives_start_offset,
+					__vdso_alternatives_end_offset);
 
 	if (IS_ENABLED(CONFIG_RISCV_USER_CFI))
-		apply_vdso_alternatives(vdso_cfi_start);
+		apply_vdso_alternatives(vdso_cfi_start,
+					__vdso_alternatives_start_cfi_offset,
+					__vdso_alternatives_end_cfi_offset);
 }
 
 /*

-- 
2.55.0