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Subject[PATCH 1/2] x86/asm/entry/32: Explain stub32_clone logic
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The reason for copying of %r8 to %rcx is quite non-obvious.
Add a comment which explains why it is done.

Fix indentation and trailing whitespace while at it.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
---
CC: Linus Torvalds <torvalds@linux-foundation.org>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Ingo Molnar <mingo@kernel.org>
CC: Borislav Petkov <bp@alien8.de>
CC: "H. Peter Anvin" <hpa@zytor.com>
CC: Andy Lutomirski <luto@amacapital.net>
CC: Oleg Nesterov <oleg@redhat.com>
CC: Frederic Weisbecker <fweisbec@gmail.com>
CC: Alexei Starovoitov <ast@plumgrid.com>
CC: Will Drewry <wad@chromium.org>
CC: Kees Cook <keescook@chromium.org>
CC: x86@kernel.org
CC: linux-kernel@vger.kernel.org
arch/x86/ia32/ia32entry.S | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S
index 2ca052e..8e72256 100644
--- a/arch/x86/ia32/ia32entry.S
+++ b/arch/x86/ia32/ia32entry.S
@@ -562,9 +562,17 @@ GLOBAL(\label)

ALIGN
GLOBAL(stub32_clone)
- leaq sys_clone(%rip),%rax
+ leaq sys_clone(%rip), %rax
+ /*
+ * 32-bit clone API is clone(..., int tls_val, int *child_tidptr).
+ * 64-bit clone API is clone(..., int *child_tidptr, int tls_val).
+ * Native 64-bit kernel's sys_clone() implements the latter.
+ * We need to swap args here. But since tls_val is in fact ignored
+ * by sys_clone(), we can get away with an assignment
+ * (arg4 = arg5) instead of a full swap:
+ */
mov %r8, %rcx
- jmp ia32_ptregs_common
+ jmp ia32_ptregs_common

ALIGN
ia32_ptregs_common:
--
1.8.1.4


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