[PATCH 3/4] x86: open-code register save/restore in trace_hardirqs thunks

From: Denys Vlasenko
Date: Thu Jan 08 2015 - 11:26:28 EST


This is a preparatory patch for change in "struct pt_regs"
handling in entry_64.S.

trace_hardirqs thunks were (ab)using a part of pt_regs
handling code, namely SAVE_ARGS/RESTORE_ARGS macros,
to save/restore registers across C function calls.

Since SAVE_ARGS is going to be changed, open-code
register saving/restoring here.

Incidentally, this removes a bit of dead code:
one SAVE_ARGS was used just to emit a CFI annotation,
but it also generated unreachable assembly insns.

Signed-off-by: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
CC: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
CC: Oleg Nesterov <oleg@xxxxxxxxxx>
CC: "H. Peter Anvin" <hpa@xxxxxxxxx>
CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
CC: Frederic Weisbecker <fweisbec@xxxxxxxxx>
CC: X86 ML <x86@xxxxxxxxxx>
CC: Alexei Starovoitov <ast@xxxxxxxxxxxx>
CC: Will Drewry <wad@xxxxxxxxxxxx>
CC: Kees Cook <keescook@xxxxxxxxxxxx>
CC: linux-kernel@xxxxxxxxxxxxxxx
---
arch/x86/lib/thunk_64.S | 29 ++++++++++++++++++++++++-----
1 file changed, 24 insertions(+), 5 deletions(-)

diff --git a/arch/x86/lib/thunk_64.S b/arch/x86/lib/thunk_64.S
index b30b5eb..03a3883 100644
--- a/arch/x86/lib/thunk_64.S
+++ b/arch/x86/lib/thunk_64.S
@@ -16,10 +16,20 @@
\name:
CFI_STARTPROC

- /* this one pushes 9 elems, the next one would be %rIP */
- SAVE_ARGS
+ subq $9*8, %rsp
+ CFI_ADJUST_CFA_OFFSET 9*8
+ movq_cfi r11, 0*8
+ movq_cfi r10, 1*8
+ movq_cfi r9, 2*8
+ movq_cfi r8, 3*8
+ movq_cfi rax, 4*8
+ movq_cfi rcx, 5*8
+ movq_cfi rdx, 6*8
+ movq_cfi rsi, 7*8
+ movq_cfi rdi, 8*8

.if \put_ret_addr_in_rdi
+ /* 9*8(%rsp) is return addr on stack */
movq_cfi_restore 9*8, rdi
.endif

@@ -45,11 +55,20 @@
#endif
#endif

- /* SAVE_ARGS below is used only for the .cfi directives it contains. */
CFI_STARTPROC
- SAVE_ARGS
+ CFI_ADJUST_CFA_OFFSET 9*8
restore:
- RESTORE_ARGS
+ movq_cfi_restore 0*8, r11
+ movq_cfi_restore 1*8, r10
+ movq_cfi_restore 2*8, r9
+ movq_cfi_restore 3*8, r8
+ movq_cfi_restore 4*8, rax
+ movq_cfi_restore 5*8, rcx
+ movq_cfi_restore 6*8, rdx
+ movq_cfi_restore 7*8, rsi
+ movq_cfi_restore 8*8, rdi
+ addq 9*8, %rsp
+ CFI_ADJUST_CFA_OFFSET -9*8
ret
CFI_ENDPROC
_ASM_NOKPROBE(restore)
--
1.8.1.4

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