[PATCH v2] x86-64/entry: add instruction suffix to SYSRET

[PATCH v2] x86-64/entry: add instruction suffix to SYSRET

[Jan Beulich]

ignore_sysret contains an unsuffixed 'sysret' instruction.  gas
correctly interprets this as sysretl, but leaving it up to gas to
guess when there is no register operand that implies a size is bad
practice, and upstream gas is likely to warn about this in the future.
Use 'sysretl' explicitly.  This does not change the assembled output.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
---
v2: Use re-written description from Andy.

--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1728,7 +1728,7 @@ END(nmi)
 SYM_CODE_START(ignore_sysret)
 	UNWIND_HINT_EMPTY
 	mov	$-ENOSYS, %eax
-	sysret
+	sysretl
 SYM_CODE_END(ignore_sysret)
 #endif
 

[tip: x86/asm] x86/entry/64: Add instruction suffix to SYSRET

[tip-bot2 for Jan Beulich]

The following commit has been merged into the x86/asm branch of tip:

Commit-ID:     b2b1d94cdfd4e906d3936dab2850096a4a0c2017
Gitweb:        https://git.kernel.org/tip/b2b1d94cdfd4e906d3936dab2850096a4a0c2017
Author:        Jan Beulich <jbeulich@suse.com>
AuthorDate:    Mon, 16 Dec 2019 11:40:03 +01:00
Committer:     Borislav Petkov <bp@suse.de>
CommitterDate: Thu, 09 Jan 2020 12:33:43 +01:00

x86/entry/64: Add instruction suffix to SYSRET

ignore_sysret() contains an unsuffixed SYSRET instruction. gas correctly
interprets this as SYSRETL, but leaving it up to gas to guess when there
is no register operand that implies a size is bad practice, and upstream
gas is likely to warn about this in the future. Use SYSRETL explicitly.
This does not change the assembled output.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lkml.kernel.org/r/038a7c35-062b-a285-c6d2-653b56585844@suse.com
---
 arch/x86/entry/entry_64.S | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index 76942cb..f2bb91e 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1728,7 +1728,7 @@ SYM_CODE_END(nmi)
 SYM_CODE_START(ignore_sysret)
 	UNWIND_HINT_EMPTY
 	mov	$-ENOSYS, %eax
-	sysret
+	sysretl
 SYM_CODE_END(ignore_sysret)
 #endif