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| author | Denys Vlasenko <dvlasenk@redhat.com> | 2015-06-03 16:58:49 +0300 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2015-06-05 14:41:27 +0300 |
| commit | 5cdc683b7d8b3341a3d18e0c5498bc1e4f3fb990 (patch) | |
| tree | cc8ec7d947f0554eee69c86b8bab16f82ed6fd5b /arch/x86/entry | |
| parent | 54ad726c51b7f7dffcc1dc379bedadee19f742f7 (diff) | |
| download | linux-5cdc683b7d8b3341a3d18e0c5498bc1e4f3fb990.tar.xz | |
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 <dvlasenk@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1433339930-20880-1-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/entry')
| -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 |