Commit-ID: 5cdc683b7d8b3341a3d18e0c5498bc1e4f3fb990 Gitweb: http://git.kernel.org/tip/5cdc683b7d8b3341a3d18e0c5498bc1e4f3fb990 Author: Denys Vlasenko <dvlasenk@xxxxxxxxxx> AuthorDate: Wed, 3 Jun 2015 15:58:49 +0200 Committer: Ingo Molnar <mingo@xxxxxxxxxx> CommitDate: Fri, 5 Jun 2015 13:41:27 +0200 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@xxxxxxxxxx> Cc: Alexei Starovoitov <ast@xxxxxxxxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Brian Gerst <brgerst@xxxxxxxxx> Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx> Cc: H. Peter Anvin <hpa@xxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Oleg Nesterov <oleg@xxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Will Drewry <wad@xxxxxxxxxxxx> Link: http://lkml.kernel.org/r/1433339930-20880-1-git-send-email-dvlasenk@xxxxxxxxxx Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx> --- arch/x86/entry/ia32entry.S | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/arch/x86/entry/ia32entry.S b/arch/x86/entry/ia32entry.S index 4bb9f7b..d0c7b28 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 -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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