lkml.org 
[lkml]   [2023]   [May]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [PATCH v6 03/20] modpost: detect section mismatch for R_ARM_MOVW_ABS_NC and R_ARM_MOVT_ABS
    + linux-arm-kernel

    On Sun, May 21, 2023 at 9:05 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
    >
    > ARM defconfig misses to detect some section mismatches.
    >
    > [test code]
    >
    > #include <linux/init.h>
    >
    > int __initdata foo;
    > int get_foo(int x) { return foo; }
    >
    > It is apparently a bad reference, but modpost does not report anything
    > for ARM defconfig (i.e. multi_v7_defconfig).
    >
    > The test code above produces the following relocations.
    >
    > Relocation section '.rel.text' at offset 0x200 contains 2 entries:
    > Offset Info Type Sym.Value Sym. Name
    > 00000000 0000062b R_ARM_MOVW_ABS_NC 00000000 .LANCHOR0
    > 00000004 0000062c R_ARM_MOVT_ABS 00000000 .LANCHOR0
    >
    > Relocation section '.rel.ARM.exidx' at offset 0x210 contains 2 entries:
    > Offset Info Type Sym.Value Sym. Name
    > 00000000 0000022a R_ARM_PREL31 00000000 .text
    > 00000000 00001000 R_ARM_NONE 00000000 __aeabi_unwind_cpp_pr0
    >
    > Currently, R_ARM_MOVW_ABS_NC and R_ARM_MOVT_ABS are just skipped.
    >
    > Add code to handle them. I checked arch/arm/kernel/module.c to learn
    > how the offset is encoded in the instruction.
    >
    > The referenced symbol in relocation might be a local anchor.
    > If is_valid_name() returns false, let's search for a better symbol name.
    >
    > Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
    > ---
    >
    > scripts/mod/modpost.c | 12 ++++++++++--
    > 1 file changed, 10 insertions(+), 2 deletions(-)
    >
    > diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
    > index 34fbbd85bfde..ed2301e951a9 100644
    > --- a/scripts/mod/modpost.c
    > +++ b/scripts/mod/modpost.c
    > @@ -1108,7 +1108,7 @@ static inline int is_valid_name(struct elf_info *elf, Elf_Sym *sym)
    > /**
    > * Find symbol based on relocation record info.
    > * In some cases the symbol supplied is a valid symbol so
    > - * return refsym. If st_name != 0 we assume this is a valid symbol.
    > + * return refsym. If is_valid_name() == true, we assume this is a valid symbol.
    > * In other cases the symbol needs to be looked up in the symbol table
    > * based on section and address.
    > * **/
    > @@ -1121,7 +1121,7 @@ static Elf_Sym *find_tosym(struct elf_info *elf, Elf64_Sword addr,
    > Elf64_Sword d;
    > unsigned int relsym_secindex;
    >
    > - if (relsym->st_name != 0)
    > + if (is_valid_name(elf, relsym))
    > return relsym;
    >
    > /*
    > @@ -1312,11 +1312,19 @@ 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);
    > Elf_Sym *sym = elf->symtab_start + ELF_R_SYM(r->r_info);
    > unsigned int inst = TO_NATIVE(*reloc_location(elf, sechdr, r));
    > + int offset;
    >
    > switch (r_typ) {
    > case R_ARM_ABS32:
    > r->r_addend = inst + sym->st_value;
    > break;
    > + case R_ARM_MOVW_ABS_NC:
    > + case R_ARM_MOVT_ABS:
    > + offset = ((inst & 0xf0000) >> 4) | (inst & 0xfff);
    > + offset = (offset ^ 0x8000) - 0x8000;

    The code in arch/arm/kernel/module.c then right shifts the offset by
    16 for R_ARM_MOVT_ABS. Is that necessary?

    > + offset += sym->st_value;
    > + r->r_addend = offset;
    > + break;
    > case R_ARM_PC24:
    > case R_ARM_CALL:
    > case R_ARM_JUMP24:
    > --
    > 2.39.2
    >


    --
    Thanks,
    ~Nick Desaulniers

    \
     
     \ /
      Last update: 2023-05-22 20:05    [W:3.020 / U:0.016 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site