diff options
| author | Denys Vlasenko <[email protected]> | 2015-06-03 15:58:49 +0200 |
|---|---|---|
| committer | Ingo Molnar <[email protected]> | 2015-06-05 13:41:27 +0200 |
| commit | 5cdc683b7d8b3341a3d18e0c5498bc1e4f3fb990 (patch) | |
| tree | cc8ec7d947f0554eee69c86b8bab16f82ed6fd5b | |
| parent | 54ad726c51b7f7dffcc1dc379bedadee19f742f7 (diff) | |
x86/asm/entry/32: Explain the stub32_clone logic
The reason for copying of %r8 to %rcx is quite non-obvious.
Add a comment which explains why it is done.
Signed-off-by: Denys Vlasenko <[email protected]>
Cc: Alexei Starovoitov <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Will Drewry <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
| -rw-r--r-- | arch/x86/entry/ia32entry.S | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/arch/x86/entry/ia32entry.S b/arch/x86/entry/ia32entry.S index 4bb9f7b2bc9c..d0c7b28d5670 100644 --- a/arch/x86/entry/ia32entry.S +++ b/arch/x86/entry/ia32entry.S @@ -528,6 +528,14 @@ GLOBAL(\label) ALIGN GLOBAL(stub32_clone) 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 |