https://sourceware.org/bugzilla/show_bug.cgi?id=20253
Bug ID: 20253
Summary: Unnecessary PLT entry for IFUNC function via GOT
Product: binutils
Version: 2.27 (HEAD)
Status: NEW
Severity: normal
Priority: P2
Component: ld
Assignee: unassigned at sourceware dot org
Reporter: hjl.tools at gmail dot com
Target Milestone: ---
Target: x86
[hjl@gnu-6 saved]$ cat x.S
.text
.globl foo
.type foo, @gnu_indirect_function
foo:
ret
.text
.type bar, @gnu_indirect_function
bar:
ret
.globl _start
.type _start, @function
_start:
#ifdef __x86_64__
call *foo@GOTPCREL(%rip)
jmp *bar@GOTPCREL(%rip)
movq $0, bar@GOTPCREL(%rip)
cmpq $0, foo@GOTPCREL(%rip)
cmpq foo@GOTPCREL(%rip), %rcx
cmpq bar@GOTPCREL(%rip), %rcx
#else
call *foo@GOT
jmp *bar@GOT
movl $0, bar@GOT
cmpl $0, foo@GOT
cmpl foo@GOT, %ecx
cmpl bar@GOT, %ecx
#endif
[hjl@gnu-6 saved]$ make x32
gcc -B./ -c -mx32 -o x32.o x.S
ld -z nocombreloc -m elf32_x86_64 -o x32 x32.o
objdump -dw x32
x32: file format elf32-x86-64
Disassembly of section .plt:
00400090 <.plt>:
400090: ff 25 62 00 20 00 jmpq *0x200062(%rip) # 6000f8
<_GLOBAL_OFFSET_TABLE_+0x18>
400096: 68 00 00 00 00 pushq $0x0
40009b: e9 00 00 00 00 jmpq 4000a0 <foo-0x10>
4000a0: ff 25 5a 00 20 00 jmpq *0x20005a(%rip) # 600100
<_GLOBAL_OFFSET_TABLE_+0x20>
4000a6: 68 00 00 00 00 pushq $0x0
4000ab: e9 00 00 00 00 jmpq 4000b0 <foo>
Disassembly of section .text:
004000b0 <foo>:
4000b0: c3 retq
004000b1 <bar>:
4000b1: c3 retq
004000b2 <_start>:
4000b2: ff 15 40 00 20 00 callq *0x200040(%rip) # 6000f8
<_GLOBAL_OFFSET_TABLE_+0x18>
4000b8: ff 25 42 00 20 00 jmpq *0x200042(%rip) # 600100
<_GLOBAL_OFFSET_TABLE_+0x20>
4000be: 48 c7 05 37 00 20 00 00 00 00 00 movq
$0x0,0x200037(%rip) # 600100 <_GLOBAL_OFFSET_TABLE_+0x20>
4000c9: 48 83 3d 27 00 20 00 00 cmpq $0x0,0x200027(%rip)
# 6000f8 <_GLOBAL_OFFSET_TABLE_+0x18>
4000d1: 48 3b 0d 20 00 20 00 cmp 0x200020(%rip),%rcx #
6000f8 <_GLOBAL_OFFSET_TABLE_+0x18>
4000d8: 48 3b 0d 21 00 20 00 cmp 0x200021(%rip),%rcx #
600100 <_GLOBAL_OFFSET_TABLE_+0x20>
[hjl@gnu-6 saved]$ make i386
gcc -B./ -c -m32 -o i386.o x.S
ld -z nocombreloc -m elf_i386 -o i386 i386.o
objdump -dw i386
i386: file format elf32-i386
Disassembly of section .plt:
08048090 <.plt>:
8048090: ff 25 e8 90 04 08 jmp *0x80490e8
8048096: 68 00 00 00 00 push $0x0
804809b: e9 00 00 00 00 jmp 80480a0 <foo-0x10>
80480a0: ff 25 ec 90 04 08 jmp *0x80490ec
80480a6: 68 00 00 00 00 push $0x0
80480ab: e9 00 00 00 00 jmp 80480b0 <foo>
Disassembly of section .text:
080480b0 <foo>:
80480b0: c3 ret
080480b1 <bar>:
80480b1: c3 ret
080480b2 <_start>:
80480b2: ff 15 e8 90 04 08 call *0x80490e8
80480b8: ff 25 ec 90 04 08 jmp *0x80490ec
80480be: c7 05 ec 90 04 08 00 00 00 00 movl $0x0,0x80490ec
80480c8: 83 3d e8 90 04 08 00 cmpl $0x0,0x80490e8
80480cf: 3b 0d e8 90 04 08 cmp 0x80490e8,%ecx
80480d5: 3b 0d ec 90 04 08 cmp 0x80490ec,%ecx
[hjl@gnu-6 saved]$ make x86_64
gcc -B./ -c -m64 -o x86_64.o x.S
ld -z nocombreloc -m elf_x86_64 -o x86_64 x86_64.o
objdump -dw x86_64
x86_64: file format elf64-x86-64
Disassembly of section .plt:
00000000004000e0 <.plt>:
4000e0: ff 25 62 00 20 00 jmpq *0x200062(%rip) # 600148
<_GLOBAL_OFFSET_TABLE_+0x18>
4000e6: 68 00 00 00 00 pushq $0x0
4000eb: e9 00 00 00 00 jmpq 4000f0 <foo-0x10>
4000f0: ff 25 5a 00 20 00 jmpq *0x20005a(%rip) # 600150
<_GLOBAL_OFFSET_TABLE_+0x20>
4000f6: 68 00 00 00 00 pushq $0x0
4000fb: e9 00 00 00 00 jmpq 400100 <foo>
Disassembly of section .text:
0000000000400100 <foo>:
400100: c3 retq
0000000000400101 <bar>:
400101: c3 retq
0000000000400102 <_start>:
400102: ff 15 40 00 20 00 callq *0x200040(%rip) # 600148
<_GLOBAL_OFFSET_TABLE_+0x18>
400108: ff 25 42 00 20 00 jmpq *0x200042(%rip) # 600150
<_GLOBAL_OFFSET_TABLE_+0x20>
40010e: 48 c7 05 37 00 20 00 00 00 00 00 movq
$0x0,0x200037(%rip) # 600150 <_GLOBAL_OFFSET_TABLE_+0x20>
400119: 48 83 3d 27 00 20 00 00 cmpq $0x0,0x200027(%rip)
# 600148 <_GLOBAL_OFFSET_TABLE_+0x18>
400121: 48 3b 0d 20 00 20 00 cmp 0x200020(%rip),%rcx #
600148 <_GLOBAL_OFFSET_TABLE_+0x18>
400128: 48 3b 0d 21 00 20 00 cmp 0x200021(%rip),%rcx #
600150 <_GLOBAL_OFFSET_TABLE_+0x20>
[hjl@gnu-6 saved]$
All of PLT entries should be removed.
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