linux-kernel - [PATCH] modpost: fix section mismatch message for R_ARM

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Message-Id: <20230515005419.1293357-1-masahiroy@kernel.org>
Date:   Mon, 15 May 2023 09:54:19 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Russell King <linux@...linux.org.uk>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nicolas Schier <nicolas@...sle.eu>,
        Sam Ravnborg <sam@...nborg.org>
Subject: [PATCH] modpost: fix section mismatch message for R_ARM_ABS32

The section mismatch check does not show proper warning messages for ARM.

Here, very simple test code.

    #include <linux/init.h>

    static int __initdata foo;

    void set_foo(int x)
    {
            foo = x;
    }

    int get_foo(int x)
    {
            return foo;
    }

If I compile it for ARM, modpost does not show the symbol name.

  WARNING: modpost: vmlinux.o: section mismatch in reference: set_foo (section: .text) -> (unknown) (section: .init.data)
  WARNING: modpost: vmlinux.o: section mismatch in reference: get_foo (section: .text) -> (unknown) (section: .init.data)

If I compile it for other architectures, modpost shows the correct symbol name.

  WARNING: modpost: vmlinux.o: section mismatch in reference: set_foo (section: .text) -> foo (section: .init.data)
  WARNING: modpost: vmlinux.o: section mismatch in reference: get_foo (section: .text) -> foo (section: .init.data)

For R_ARM_ABS32, addend_arm_rel() sets r->r_addend to a wrong value.

arch/arm/kernel/module.c handles R_ARM_ABS32 as follows:

        case R_ARM_ABS32:
        case R_ARM_TARGET1:
                *(u32 *)loc += sym->st_value;

I just mimicked it in modpost.

Fixes: 56a974fa2d59 ("kbuild: make better section mismatch reports on arm")
Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
---

 scripts/mod/modpost.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index d4531d09984d..c93780d93caf 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -1460,12 +1460,13 @@ static int addend_386_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r)
 static int addend_arm_rel(struct elf_info *elf, Elf_Shdr *sechdr, Elf_Rela *r)
 {
 	unsigned int r_typ = ELF_R_TYPE(r->r_info);
+	unsigned int *location = reloc_location(elf, sechdr, r);
+	Elf_Sym *sym;
 
 	switch (r_typ) {
 	case R_ARM_ABS32:
-		/* From ARM ABI: (S + A) | T */
-		r->r_addend = (int)(long)
-			      (elf->symtab_start + ELF_R_SYM(r->r_info));
+		sym = elf->symtab_start + ELF_R_SYM(r->r_info);
+		r->r_addend = TO_NATIVE(*location) + sym->st_value;
 		break;
 	case R_ARM_PC24:
 	case R_ARM_CALL:
-- 
2.39.2