| From 74edb473c9ecf5e2053ecf8e429ee608feafb9e1 Mon Sep 17 00:00:00 2001 |
| From: Tamar Christina <tamar.christina@arm.com> |
| Date: Thu, 1 Apr 2021 17:10:38 +0100 |
| Subject: [PATCH] PE/Windows x86_64: Fix weak undef symbols after image base |
| change |
| |
| The change in PR19011 changed the image load address from being in the lower |
| 32-bit address space to the higher 64-bit address space. |
| |
| However when you have a weak undef symbol which stays undef at the end of |
| linking the linker has to resolve this (Windows loader does not support undef |
| symbols). As such typically these would resolve to 0. |
| |
| The relocation used for these weak symbols are the normal 32-bit PC_REL call |
| relocs. So when doing the overflow check LD checks if the distance between the |
| symbol and the call is within range. However now that the load address is |
| > 32-bits and the symbol val is 0 this overflow check will always fail. |
| |
| As such the linker gives a bogus error. This patch makes the linker not emit |
| the overflow failure but chooses to still let the check be performed (as it's |
| mid-end code). |
| |
| One down side of this is that it does break the common convention that the call |
| be to sym at 0x0. i.e. before you'd get |
| |
| 401015: 74 05 je 40101c |
| 401017: e8 e4 ef bf ff callq 0 |
| |
| and now you get |
| |
| 140001015: 74 05 je 14000101c |
| 140001017: e8 e4 ef ff bf call 100000000 |
| |
| since the call is PC_REL there's no way to get the range large enough to |
| resolve to 0. As such I have chosen to leave it as the furthest simple range |
| that we can still represent. |
| |
| By only ignoring the error we leave the symbol value itself to still be 0 |
| such that the if(<symbol>) checks still work correctly. |
| |
| bfd/ChangeLog: |
| |
| 2021-04-01 Tamar Christina <tamar.christina@arm.com> |
| |
| PR ld/26659 |
| * cofflink.c (_bfd_coff_generic_relocate_section): Ignore overflow. |
| |
| ld/ChangeLog: |
| |
| 2021-04-01 Tamar Christina <tamar.christina@arm.com> |
| |
| PR ld/26659 |
| * testsuite/ld-pe/pe.exp: Add test. |
| * testsuite/ld-pe/pr26659-weak-undef-sym.d: New test. |
| * testsuite/ld-pe/pr26659-weak-undef-sym.s: New test. |
| --- |
| bfd/ChangeLog | 5 +++ |
| bfd/cofflink.c | 15 ++++++++ |
| ld/ChangeLog | 7 ++++ |
| ld/testsuite/ld-pe/pe.exp | 1 + |
| ld/testsuite/ld-pe/pr26659-weak-undef-sym.d | 32 +++++++++++++++++ |
| ld/testsuite/ld-pe/pr26659-weak-undef-sym.s | 38 +++++++++++++++++++++ |
| 6 files changed, 98 insertions(+) |
| create mode 100644 ld/testsuite/ld-pe/pr26659-weak-undef-sym.d |
| create mode 100644 ld/testsuite/ld-pe/pr26659-weak-undef-sym.s |
| |
| diff --git a/bfd/cofflink.c b/bfd/cofflink.c |
| index c6b65c761d7..dd3e8dd4bf6 100644 |
| --- a/bfd/cofflink.c |
| +++ b/bfd/cofflink.c |
| @@ -3129,6 +3129,21 @@ _bfd_coff_generic_relocate_section (bfd *output_bfd, |
| return false; |
| case bfd_reloc_overflow: |
| { |
| + |
| + /* Ignore any weak undef symbols that may have overflowed. Due to |
| + PR ld/19011 the base address is now in the upper 64-bit address |
| + range. This means that when _bfd_final_link_relocate calculates |
| + the overlow it takes the distance between the symbol and the VMA |
| + which will now always overflow as 0 - 64-bit addr > 32-bit range |
| + of the relocation. This ends up creating PR ld/26659. */ |
| + if (val == 0 |
| + /* Reverse the hack where 4 is subtracted from the addend. */ |
| + && (addend + 4) == 0 |
| + && sym->n_sclass == C_NT_WEAK |
| + && bfd_coff_classify_symbol (output_bfd, sym) |
| + == COFF_SYMBOL_UNDEFINED) |
| + break; |
| + |
| const char *name; |
| char buf[SYMNMLEN + 1]; |
| |
| diff --git a/ld/testsuite/ld-pe/pe.exp b/ld/testsuite/ld-pe/pe.exp |
| index b1a200180be..a536b51c3e6 100644 |
| --- a/ld/testsuite/ld-pe/pe.exp |
| +++ b/ld/testsuite/ld-pe/pe.exp |
| @@ -81,6 +81,7 @@ run_dump_test "reloc" |
| run_dump_test "weakdef-1" |
| |
| run_dump_test "pr19803" |
| +run_dump_test "pr26659-weak-undef-sym" |
| set pr19803_dll { |
| { "PR 19803: not exporting swept symbols" |
| "-shared --out-implib dx.dll --gc-sections" |
| diff --git a/ld/testsuite/ld-pe/pr26659-weak-undef-sym.d b/ld/testsuite/ld-pe/pr26659-weak-undef-sym.d |
| new file mode 100644 |
| index 00000000000..0b48994877d |
| --- /dev/null |
| +++ b/ld/testsuite/ld-pe/pr26659-weak-undef-sym.d |
| @@ -0,0 +1,32 @@ |
| +#source: pr26659-weak-undef-sym.s |
| +#target: x86_64-*-cygwin* x86_64-*-pe x86_64-*-mingw* |
| +#ld: -e0 |
| +#objdump: -d |
| + |
| +#... |
| +0000000140001000 <foo>: |
| + 140001000: 55 push %rbp |
| + 140001001: 48 89 e5 mov %rsp,%rbp |
| + 140001004: 48 83 ec 20 sub \$0x20,%rsp |
| + 140001008: 89 4d 10 mov %ecx,0x10\(%rbp\) |
| + 14000100b: 48 8b 05 ee 0f 00 00 mov 0xfee\(%rip\),%rax # 140002000 <__data_end__> |
| + 140001012: 48 85 c0 test %rax,%rax |
| + 140001015: 74 05 je 14000101c <foo\+0x1c> |
| + 140001017: e8 e4 ef ff bf call 100000000 <__size_of_stack_reserve__\+0xffe00000> |
| + 14000101c: 48 8b 05 ed 0f 00 00 mov 0xfed\(%rip\),%rax # 140002010 <.refptr.bar2> |
| + 140001023: 48 85 c0 test %rax,%rax |
| + 140001026: 74 05 je 14000102d <foo\+0x2d> |
| + 140001028: e8 d3 ef ff bf call 100000000 <__size_of_stack_reserve__\+0xffe00000> |
| + 14000102d: 8b 45 10 mov 0x10\(%rbp\),%eax |
| + 140001030: 0f af c0 imul %eax,%eax |
| + 140001033: 48 83 c4 20 add \$0x20,%rsp |
| + 140001037: 5d pop %rbp |
| + 140001038: c3 ret |
| + 140001039: 90 nop |
| + 14000103a: 90 nop |
| + 14000103b: 90 nop |
| + 14000103c: 90 nop |
| + 14000103d: 90 nop |
| + 14000103e: 90 nop |
| + 14000103f: 90 nop |
| +#pass |
| diff --git a/ld/testsuite/ld-pe/pr26659-weak-undef-sym.s b/ld/testsuite/ld-pe/pr26659-weak-undef-sym.s |
| new file mode 100644 |
| index 00000000000..7a42759e752 |
| --- /dev/null |
| +++ b/ld/testsuite/ld-pe/pr26659-weak-undef-sym.s |
| @@ -0,0 +1,38 @@ |
| + .text |
| + .globl foo |
| + .def foo; .scl 2; .type 32; .endef |
| +foo: |
| + pushq %rbp |
| + movq %rsp, %rbp |
| + subq $32, %rsp |
| + movl %ecx, 16(%rbp) |
| + movq .refptr.bar1(%rip), %rax |
| + testq %rax, %rax |
| + je .L2 |
| + call bar1 |
| +.L2: |
| + movq .refptr.bar2(%rip), %rax |
| + testq %rax, %rax |
| + je .L3 |
| + call bar2 |
| +.L3: |
| + movl 16(%rbp), %eax |
| + imull %eax, %eax |
| + addq $32, %rsp |
| + popq %rbp |
| + ret |
| + .weak bar2 |
| + .weak bar1 |
| + .def bar1; .scl 2; .type 32; .endef |
| + .def bar2; .scl 2; .type 32; .endef |
| + .section .rdata$.refptr.bar2, "dr" |
| + .globl .refptr.bar2 |
| + .linkonce discard |
| +.refptr.bar2: |
| + .quad bar2 |
| + .section .rdata$.refptr.bar1, "dr" |
| + .globl .refptr.bar1 |
| + .linkonce discard |
| +.refptr.bar1: |
| + .quad bar1 |
| + |
| -- |
| 2.27.0 |
| |
