arch/arm/lib: Fix the assembly sources for the kernel build by LLVM #5718
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The LLVM assembler is stricter on the source syntax than GCC. - Prepend a backslash (\) to each macro argument. - The condition field is always the last portion of an instruction mnemonic. - The terms of the relational operators in a conditional assemble directive are integers, not strings. The assembly source files complying above assemble by both LLVM and GCC / Binutils. Signed-off-by: Seigo Tanimura <seigo.tanimura@gmail.com>
iucoen
reviewed
Nov 19, 2023
| ands DAT2, D, #15 | ||
| beq 164f | ||
| .else | ||
| ands DAT2, D, #15 | ||
| beq 164f | ||
| rsb DAT2, DAT2, #16 | ||
| .endif | ||
| memcpy_leading_15bytes backwards, align | ||
| memcpy_leading_15bytes \backwards, 1 |
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Should this be \align ?
Align is not an argument to this macro. How did the old code even compile?
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I want to know why, too 😂
The test assembly source for a quick reproduction
.text
.arch armv6
.object_arch armv4
.arm
.p2align 2
.macro should_not_assemble_macro arg
.if \arg == 0
add a1, a2, #4
.else
sub a1, a3, #2
.endif
.endm
should_not_assemble:
should_not_assemble_macro arg
.type should_not_assemble, %function
.end
GCC
(raspbian-bookworm-armhf)a130ft@berget:~/work/should-not-assemble$ gcc -o should-not-assemble.o -c should-not-assemble.S
(raspbian-bookworm-armhf)a130ft@berget:~/work/should-not-assemble$ objdump --disassemble should-not-assemble.o
should-not-assemble.o: file format elf32-littlearm
Disassembly of section .text:
00000000 <should_not_assemble>:
0: e2420002 sub r0, r2, #2
(raspbian-bookworm-armhf)a130ft@berget:~/work/should-not-assemble$
LLVM (clang)
(raspbian-bookworm-armhf)a130ft@berget:~/work/should-not-assemble$ clang -o should-not-assemble.o -c should-not-assemble.S
<instantiation>:1:5: error: expected absolute expression
.if arg == 0
^
should-not-assemble.S:16:5: note: while in macro instantiation
should_not_assemble_macro arg
^
(raspbian-bookworm-armhf)a130ft@berget:~/work/should-not-assemble$
So gcc insists that arg == 0 expanded out of \arg == 0 has the acceptable syntax and evaluates to false.
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The LLVM assembler is stricter on the source syntax than GCC.
Prepend a backslash () to each macro argument.
The condition field is always the last portion of an instruction mnemonic.
The terms of the relational operators in a conditional assemble directive are integers, not strings.
The assembly source files complying above assemble by both LLVM and GCC / Binutils.
Issue: 5295
Build tested on: clang 14.0.6 and gcc Raspbian 12.2.0-14+rpi1, both armhf native on qemu-static.
Kernel exec tested on: Raspberry Pi 3B+ and Zero W.