https://llvm.org/bugs/show_bug.cgi?id=24072
Bug ID: 24072
Summary: [x86 assembler] no error diagnostic for out-of-range
jrcxz/jecxz/jcxz
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: Backend: X86
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
X86 instructions jrcxz/jecxz/jcxz performs short jumps if rcx/ecx/cx register
is 0
The maximum relative offset for a forward short jump is 127 Bytes (0x7F).
The maximum relative offset for a backward short jump is 128 Bytes (0x80).
Gnu assembler warns when the distance of the jump exceeds the maximum but
llvm-as does not.
Here are 3 examples:
/*******************************************************************/
> cat jecxz.s
.balign 256
jecxz foo
.balign 256
foo:
> clang jecxz.s –c
(no error)
> gcc jecxz.s -c
jecxz.s: Assembler messages:
jecxz.s:2: Error: value of 253 too large for field of 1 bytes at 2
/*******************************************************************/
> cat jrcxz.s
.balign 256
jrcxz foo
.balign 256
foo:
> clang jrcxz.s -c -m64
(no error)
> gcc jrcxz.s -c -m64
jrcxz.s: Assembler messages:
jrcxz.s:2: Error: value of 254 too large for field of 1 bytes at 1
/*******************************************************************/
> cat jcxz.s
.balign 256
jcxz foo
.balign 256
foo:
> clang jcxz.s -c -m32
(no error)
> gcc jcxz.s -c -m32
jcxz.s: Assembler messages:
jcxz.s:2: Error: value of 253 too large for field of 1 bytes at 2
/*******************************************************************/
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