MIPS: VDSO: Avoid including .got in dynamic segment

After commit 2db1ec80dfd5 ("MIPS: VDSO: Fold MIPS_DISABLE_VDSO into
MIPS_GENERIC_GETTIMEOFDAY"), building ARCH=mips allnoconfig with LLVM=1
shows some warnings from llvm-readelf while checking the VDSO for
dynamic relocations:

  llvm-readelf: warning: 'arch/mips/vdso/vdso.so.dbg.raw': invalid PT_DYNAMIC size (0xa4)
  llvm-readelf: warning: 'arch/mips/vdso/vdso.so.dbg.raw': PT_DYNAMIC dynamic table is invalid: SHT_DYNAMIC will be used

The blamed commit alters the link order of objects into vdso.so.raw,
placing vgettimeofday.o after sigreturn.o. This ultimately results in
the .text section shrinking slightly in size, which in turn changes the
offset of the .dynamic section.

  -  [ 9] .text             PROGBITS        000002f0 0002f0 000930 00  AX  0   0 16
  -  [10] .dynamic          DYNAMIC         00000c20 000c20 000090 08   A  5   0  4
  +  [ 9] .text             PROGBITS        000002f0 0002f0 000924 00  AX  0   0 16
  +  [10] .dynamic          DYNAMIC         00000c14 000c14 000090 08   A  5   0  4

Changing the offset of the .dynamic section causes the dynamic segment
size to grow by the same amount, which triggers a warning in
llvm-readelf because PT_DYNAMIC's p_filesz (0xa4) is no longer a
multiple of its sh_entsize (8):

  -  DYNAMIC        0x000c20 0x00000c20 0x00000c20 0x00098 0x00098 R   0x10
  +  DYNAMIC        0x000c14 0x00000c14 0x00000c14 0x000a4 0x000a4 R   0x10

The size of the dynamic segment was already incorrect before the blamed
comment, as it should be 0x90 like the .dynamic section above (18
entries at 8 bytes per entry); it just so happens that 0x98 % 8 is 0,
whereas 0xa4 % 8 is 4, so there was no warning.

Looking at the section to segment mapping of the dynamic segment reveals
that it includes the .got section, as it is implicitly placed after
.dynamic by ld.lld's orphan section heuristics and inherits its segments
from the linker script.

  [ 9] .text             PROGBITS        000002f0 0002f0 000924 00  AX  0   0 16
  [10] .dynamic          DYNAMIC         00000c14 000c14 000090 08   A  5   0  4
  [11] .got              PROGBITS        00000cb0 000cb0 000008 00 WAp  0   0 16

  Section to Segment mapping:
   Segment Sections...
    00     .mips_abiflags
    01     .reginfo
    02     .mips_abiflags .reginfo .hash .dynsym .dynstr .gnu.version .gnu.version_d .note .text .dynamic .got
    03     .dynamic .got
    04     .note

Explicitly describe the .got section in the MIPS VDSO linker script
after .rodata, which switches back to the default text segment,
resulting in a dynamic segment that is the exact size of the .dynamic
section as expected with no other layout changes.

  -  DYNAMIC        0x000c14 0x00000c14 0x00000c14 0x000a4 0x000a4 R   0x10
  +  DYNAMIC        0x000c14 0x00000c14 0x00000c14 0x00090 0x00090 R   0x4

  -   03     .dynamic .got
  +   03     .dynamic

Closes: https://github.com/ClangBuiltLinux/linux/issues/2166
Fixes: 2db1ec80dfd5 ("MIPS: VDSO: Fold MIPS_DISABLE_VDSO into MIPS_GENERIC_GETTIMEOFDAY")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Acked-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

0 files changed, 0 insertions, 0 deletions