[2/2] s390: Avoid reloc overflows on undefined weak symbols (cont)
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Commit Message
This complements and reuses logic from Andreas Krebbel's commit
896a639babe2 ("s390: Avoid reloc overflows on undefined weak symbols").
Replace relative long addressing instructions of weak symbols, which
will definitely resolve to zero, with either a load address of 0 or a
a trapping insn.
This prevents the PLT32DBL relocation from overflowing in case the
binary will be loaded at 4GB or more.
bfd/
* elf64-s390.c (elf_s390_relocate_section): Replace
instructions using undefined weak symbols with relative
addressing to avoid relocation overflows.
ld/
* testsuite/ld-s390/s390.exp: Add new test.
* testsuite/ld-s390/weakundef-2.s: New test.
* testsuite/ld-s390/weakundef-2.dd: Likewise.
Reported-by: Alexander Gordeev <agordeev@linux.ibm.com>
Suggested-by: Ilya Leoshkevich <iii@linux.ibm.com>
Suggested-by: Andreas Krebbel <krebbel@linux.ibm.com>
Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---
bfd/elf64-s390.c | 37 +++++++++++++++++++++++++++++
ld/testsuite/ld-s390/s390.exp | 5 +++-
ld/testsuite/ld-s390/weakundef-2.dd | 17 +++++++++++++
ld/testsuite/ld-s390/weakundef-2.s | 17 +++++++++++++
4 files changed, 75 insertions(+), 1 deletion(-)
create mode 100644 ld/testsuite/ld-s390/weakundef-2.dd
create mode 100644 ld/testsuite/ld-s390/weakundef-2.s
Comments
On 6/26/24 17:20, Jens Remus wrote:
> This complements and reuses logic from Andreas Krebbel's commit
> 896a639babe2 ("s390: Avoid reloc overflows on undefined weak symbols").
>
> Replace relative long addressing instructions of weak symbols, which
> will definitely resolve to zero, with either a load address of 0 or a
> a trapping insn.
>
> This prevents the PLT32DBL relocation from overflowing in case the
> binary will be loaded at 4GB or more.
>
> bfd/
> * elf64-s390.c (elf_s390_relocate_section): Replace
> instructions using undefined weak symbols with relative
> addressing to avoid relocation overflows.
>
> ld/
> * testsuite/ld-s390/s390.exp: Add new test.
> * testsuite/ld-s390/weakundef-2.s: New test.
> * testsuite/ld-s390/weakundef-2.dd: Likewise.
>
> Reported-by: Alexander Gordeev <agordeev@linux.ibm.com>
> Suggested-by: Ilya Leoshkevich <iii@linux.ibm.com>
> Suggested-by: Andreas Krebbel <krebbel@linux.ibm.com>
> Signed-off-by: Jens Remus <jremus@linux.ibm.com>
Ok. Thanks!
Andreas
@@ -2399,6 +2399,43 @@ elf_s390_relocate_section (bfd *output_bfd,
/* We didn't make a PLT entry for this symbol. This
happens when statically linking PIC code, or when
using -Bsymbolic. */
+
+ /* Replace relative long addressing instructions of weak
+ symbols, which will definitely resolve to zero, with
+ either a load address of 0 or a trapping insn.
+ This prevents the PLT32DBL relocation from overflowing in
+ case the binary will be loaded at 4GB or more. */
+ if (h->root.type == bfd_link_hash_undefweak
+ && !h->root.linker_def
+ && (bfd_link_executable (info)
+ || ELF_ST_VISIBILITY (h->other) != STV_DEFAULT)
+ && r_type == R_390_PLT32DBL
+ && rel->r_offset >= 2)
+ {
+ void *insn_start = contents + rel->r_offset - 2;
+ uint16_t op = bfd_get_16 (input_bfd, insn_start) & 0xff0f;
+ uint8_t reg = bfd_get_8 (input_bfd, insn_start + 1) & 0xf0;
+
+ /* NOTE: The order of the if's is important! */
+ /* Replace load address relative long (larl) with load
+ address (lay) */
+ if (op == 0xc000)
+ {
+ /* larl rX,<weak sym> -> lay rX,0(0) */
+ bfd_put_16 (output_bfd, 0xe300 | reg, insn_start);
+ bfd_put_32 (output_bfd, 0x71, insn_start + 2);
+ continue;
+ }
+ /* Replace branch relative and save long (brasl) with a trap. */
+ else if (op == 0xc005)
+ {
+ /* brasl rX,<weak sym> -> jg .+2 (6-byte trap) */
+ bfd_put_16 (output_bfd, 0xc0f4, insn_start);
+ bfd_put_32 (output_bfd, 0x1, insn_start + 2);
+ continue;
+ }
+ }
+
break;
}
if (s390_is_ifunc_symbol_p (h))
@@ -95,9 +95,12 @@ set s390xtests {
"-m64" {pltoffset-1.s}
{{objdump "-dzrj.text --stop-address=16" pltoffset-1.dd}}
"pltoffset-1"}
- {"WEAKUNDEF1: overflow test"
+ {"WEAKUNDEF1: overflow test (PC32DBL)"
"-m elf64_s390 -dT 8GB.ld --no-error-rwx-segments" "" "-m64" {weakundef-1.s}
{{objdump "-dzrj.text" weakundef-1.dd}} "weakundef-1"}
+ {"WEAKUNDEF2: overflow test (PLT32DBL)"
+ "-m elf64_s390 -dT 8GB.ld --no-error-rwx-segments -no-pie" "" "-m64" {weakundef-2.s}
+ {{objdump "-dzrj.text" weakundef-2.dd}} "weakundef-2"}
}
if [istarget "s390-*-*"] {
new file mode 100644
@@ -0,0 +1,17 @@
+tmpdir/weakundef-2: file format elf64-s390
+
+Disassembly of section .text:
+
+0+200000000 <foo>:
+.*: c0 10 00 00 00 12 [ ]*larl %r1,200000024 <d>
+.*: c0 10 00 00 00 10 [ ]*larl %r1,200000026 <wd>
+.*: e3 10 00 00 00 71 [ ]*lay %r1,0
+.*: c0 e5 00 00 00 09 [ ]*brasl %r14,200000024 <d>
+.*: c0 e5 00 00 00 07 [ ]*brasl %r14,200000026 <wd>
+.*: c0 f4 00 00 00 01 [ ]*jg .*
+
+0+200000024 <d>:
+.*: 07 fe [ ]*br %r14
+
+0+200000026 <wd>:
+.*: 07 fe [ ]*br %r14
new file mode 100644
@@ -0,0 +1,17 @@
+.text
+ .globl foo
+foo:
+ larl %r1,d@PLT
+ larl %r1,wd@PLT
+ larl %r1,wu@PLT
+ brasl %r14,d@PLT
+ brasl %r14,wd@PLT
+ brasl %r14,wu@PLT
+ .weak wu
+ .type d,@function
+d:
+ br %r14
+ .weak wd
+ .type wd,@function
+wd:
+ br %r14