[iA] LOCAL label .altmacro syntax unsupported

[nickdesaulniers]

Bugzilla Link	45051
Version	unspecified
OS	Linux
Blocks	#4440
CC	@jcai19,@echristo,@MaskRay,@isanbard,@zygoloid,@lenary,@stephenhines

Extended Description

Buiding the RISC-V Linux kernel w/ Clang, we hit this error, ex:

.altmacro
.macro foo
LOCAL bar
bar:
jmp bar
.endm

foo

:1:1: error: invalid instruction mnemonic 'local'

We can work around this via local labels, ie:

.macro foo
1:
jmp 1b
.endm

foo

https://sourceware.org/binutils/docs/as/Macro.html#Macro documents LOCAL:
Warning: LOCAL is only available if you select “alternate macro syntax” with ‘--alternate’ or .altmacro. See .altmacro.

https://sourceware.org/binutils/docs/as/Altmacro.html#Altmacro

[nickdesaulniers]

assigned to @jcai19

[lenary]

This looks like a general problem with LLVM's assembler support for LOCAL in .altmacro systems.

[jcai19]

I can confirm this issue is target-independent. I wrote a small piece piece of code to help myself understand the exact meaning of LOCAL. I'm putting it down for future reference.

$ cat foo.s
.altmacro
.set x, 0

.macro write arg
.set x, \arg
mov x, %eax
.endm

.macro read
mov x, %ebx
.endm

write 16
read

$ as foo.s -o gas.o
$ objdump -d gas.o

gas.o: file format elf64-x86-64

Disassembly of section .text:

0000000000000000 <.text>:
0: 8b 04 25 10 00 00 00 mov 0x10,%eax
7: 8b 1c 25 10 00 00 00 mov 0x10,%ebx

Without LOCAL, the value of symbol "x" defined in the expansion of foo got read in the macro expansion of bar. If I make "x" local in foo, then it's renamed uniquely for each expansion of foo, and as a result bar would read its initial value 0 instead.

$ cat foo.s
.altmacro
.set x, 0

.macro write arg
LOCAL x
.set x, \arg
mov x, %eax
.endm

.macro read
mov x, %ebx
.endm

write 16
read

$ as foo.s -o gas.o
$ objdump -d gas.o

gas.o: file format elf64-x86-64

Disassembly of section .text:

0000000000000000 <.text>:
0: 8b 04 25 10 00 00 00 mov 0x10,%eax
7: 8b 1c 25 00 00 00 00 mov 0x0,%ebx

[jcai19]

Sent https://reviews.llvm.org/D105720 for review.

[paulmenzel]

Is issue #48543 a duplicate of this here?

[llvmbot]

@llvm/issue-subscribers-backend-x86

Author: Nick Desaulniers (nickdesaulniers)

| | | | --- | --- | | Bugzilla Link | [45051](https://llvm.org/bz45051) | | Version | unspecified | | OS | Linux | | Blocks | llvm/llvm-project#4440 | | CC | @jcai19,@echristo,@MaskRay,@isanbard,@zygoloid,@lenary,@stephenhines |

Extended Description

Buiding the RISC-V Linux kernel w/ Clang, we hit this error, ex:

.altmacro
.macro foo
LOCAL bar
bar:
jmp bar
.endm

foo

<instantiation>:1:1: error: invalid instruction mnemonic 'local'

We can work around this via local labels, ie:

.macro foo
1:
jmp 1b
.endm

foo

https://sourceware.org/binutils/docs/as/Macro.html#Macro documents LOCAL:
Warning: LOCAL is only available if you select “alternate macro syntax” with ‘--alternate’ or .altmacro. See .altmacro.

https://sourceware.org/binutils/docs/as/Altmacro.html#Altmacro