Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit eb7c11ee authored by Marc Zyngier's avatar Marc Zyngier Committed by Catalin Marinas
Browse files

arm64: alternative: Work around .inst assembler bugs 



AArch64 toolchains suffer from the following bug:

$ cat blah.S
1:
	.inst	0x01020304
	.if ((. - 1b) != 4)
		.error	"blah"
	.endif
$ aarch64-linux-gnu-gcc -c blah.S
blah.S: Assembler messages:
blah.S:3: Error: non-constant expression in ".if" statement

which precludes the use of msr_s and co as part of alternatives.

We workaround this issue by not directly testing the labels
themselves, but by moving the current output pointer by a value
that should always be zero. If this value is not null, then
we will trigger a backward move, which is expclicitely forbidden.
This triggers the error we're after:

  AS      arch/arm64/kvm/hyp.o
arch/arm64/kvm/hyp.S: Assembler messages:
arch/arm64/kvm/hyp.S:1377: Error: attempt to move .org backwards
scripts/Makefile.build:294: recipe for target 'arch/arm64/kvm/hyp.o' failed
make[1]: *** [arch/arm64/kvm/hyp.o] Error 1
Makefile:946: recipe for target 'arch/arm64/kvm' failed

Not pretty, but at least works on the current toolchains.

Acked-by: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 8d883b23

arch/arm64/include/asm/alternative.h

+18 −7
Original line number Diff line number Diff line
@@ -26,7 +26,20 @@ void free_alternatives_memory(void); 
	" .byte 662b-661b\n"				/* source len      */ \

	" .byte 664f-663f\n"				/* replacement len */



/* alternative assembly primitive: */

/*

 * alternative assembly primitive:

 *

 * If any of these .org directive fail, it means that insn1 and insn2

 * don't have the same length. This used to be written as

 *

 * .if ((664b-663b) != (662b-661b))

 * 	.error "Alternatives instruction length mismatch"

 * .endif

 *

 * but most assemblers die if insn1 or insn2 have a .inst. This should

 * be fixed in a binutils release posterior to 2.25.51.0.2 (anything

 * containing commit 4e4d08cf7399b606 or c1baaddf8861).

 */

#define ALTERNATIVE(oldinstr, newinstr, feature)			\

	"661:\n\t"							\

	oldinstr "\n"							\
@@ -39,9 +52,8 @@ void free_alternatives_memory(void); 
	newinstr "\n"							\

	"664:\n\t"							\

	".popsection\n\t"						\

	".if ((664b-663b) != (662b-661b))\n\t"				\

	"	.error \"Alternatives instruction length mismatch\"\n\t"\

	".endif\n"

	".org	. - (664b-663b) + (662b-661b)\n\t"			\

	".org	. - (662b-661b) + (664b-663b)\n"



#else
@@ -61,9 +73,8 @@ void free_alternatives_memory(void); 
	.pushsection .altinstr_replacement, "ax"

663:	\insn2

664:	.popsection

	.if ((664b-663b) != (662b-661b))

		.error "Alternatives instruction length mismatch"

	.endif

	.org	. - (664b-663b) + (662b-661b)

	.org	. - (662b-661b) + (664b-663b)

.endm



#endif  /*  __ASSEMBLY__  */