Messages in this thread Patch in this message | | | From | Denys Vlasenko <> | Subject | [PATCH 1/2] x86/asm/entry/32: Explain stub32_clone logic | Date | Wed, 22 Apr 2015 18:40:07 +0200 |
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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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