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PE/Windows x86_64: Fix weak undef symbols after image base change

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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.
This commit is contained in:
Tamar Christina 2021-04-01 17:10:38 +01:00
parent caaf412e98
commit 74edb473c9
6 changed files with 98 additions and 0 deletions
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5
bfd/ChangeLog
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@ -1,3 +1,8 @@
2021-04-01 Tamar Christina <tamar.christina@arm.com>
PR ld/26659
* cofflink.c (_bfd_coff_generic_relocate_section): Ignore overflow.
2021-04-01 Martin Liska <mliska@suse.cz>
* ecoff.c (strneq): Remove strneq and use startswith.

15
bfd/cofflink.c
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@ -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];

7
ld/ChangeLog
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@ -1,3 +1,10 @@
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.
2021-04-01 Martin Liska <mliska@suse.cz>
* ldbuildid.c (strneq): Remove strneq and use startswith.

1
ld/testsuite/ld-pe/pe.exp
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@ -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"

32
ld/testsuite/ld-pe/pr26659-weak-undef-sym.d Normal file
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@ -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

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ld/testsuite/ld-pe/pr26659-weak-undef-sym.s Normal file
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@ -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