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[Bug gas/25789] [as] x86: duplicate jmp when .nops and jmp are used toge
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From: |
hjl.tools at gmail dot com |
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Subject: |
[Bug gas/25789] [as] x86: duplicate jmp when .nops and jmp are used together |
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Date: |
Mon, 06 Apr 2020 12:12:19 +0000 |
https://sourceware.org/bugzilla/show_bug.cgi?id=25789
H.J. Lu <hjl.tools at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |RESOLVED
Resolution|--- |INVALID
--- Comment #1 from H.J. Lu <hjl.tools at gmail dot com> ---
Gas limits number of executed NOP paddings to 7 NOPs:
[hjl@gnu-cfl-2 tmp]$ cat x.s
foo:
ret
.p2align 7
mov %eax,%eax
[hjl@gnu-cfl-2 tmp]$ gcc -c x.s
[hjl@gnu-cfl-2 tmp]$ objdump -dw x.o
x.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <foo>:
0: c3 retq
1: eb 7d jmp 80 <foo+0x80>
3: 66 66 2e 0f 1f 84 00 00 00 00 00 data16 nopw
%cs:0x0(%rax,%rax,1)
e: 66 66 2e 0f 1f 84 00 00 00 00 00 data16 nopw
%cs:0x0(%rax,%rax,1)
19: 66 66 2e 0f 1f 84 00 00 00 00 00 data16 nopw
%cs:0x0(%rax,%rax,1)
24: 66 66 2e 0f 1f 84 00 00 00 00 00 data16 nopw
%cs:0x0(%rax,%rax,1)
2f: 66 66 2e 0f 1f 84 00 00 00 00 00 data16 nopw
%cs:0x0(%rax,%rax,1)
3a: 66 66 2e 0f 1f 84 00 00 00 00 00 data16 nopw
%cs:0x0(%rax,%rax,1)
45: 66 66 2e 0f 1f 84 00 00 00 00 00 data16 nopw
%cs:0x0(%rax,%rax,1)
50: 66 66 2e 0f 1f 84 00 00 00 00 00 data16 nopw
%cs:0x0(%rax,%rax,1)
5b: 66 66 2e 0f 1f 84 00 00 00 00 00 data16 nopw
%cs:0x0(%rax,%rax,1)
66: 66 66 2e 0f 1f 84 00 00 00 00 00 data16 nopw
%cs:0x0(%rax,%rax,1)
71: 66 66 2e 0f 1f 84 00 00 00 00 00 data16 nopw
%cs:0x0(%rax,%rax,1)
7c: 0f 1f 40 00 nopl 0x0(%rax)
80: 89 c0 mov %eax,%eax
[hjl@gnu-cfl-2 tmp]$ cat x.s
foo:
ret
.p2align 6
mov %eax,%eax
[hjl@gnu-cfl-2 tmp]$ gcc -c x.s
[hjl@gnu-cfl-2 tmp]$ objdump -dw x.o
x.o: file format elf64-x86-64
Disassembly of section .text:
0000000000000000 <foo>:
0: c3 retq
1: 66 66 2e 0f 1f 84 00 00 00 00 00 data16 nopw
%cs:0x0(%rax,%rax,1)
c: 66 66 2e 0f 1f 84 00 00 00 00 00 data16 nopw
%cs:0x0(%rax,%rax,1)
17: 66 66 2e 0f 1f 84 00 00 00 00 00 data16 nopw
%cs:0x0(%rax,%rax,1)
22: 66 66 2e 0f 1f 84 00 00 00 00 00 data16 nopw
%cs:0x0(%rax,%rax,1)
2d: 66 66 2e 0f 1f 84 00 00 00 00 00 data16 nopw
%cs:0x0(%rax,%rax,1)
38: 0f 1f 84 00 00 00 00 00 nopl 0x0(%rax,%rax,1)
40: 89 c0 mov %eax,%eax
[hjl@gnu-cfl-2 tmp]$
--
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