From 84c6f6046c5a2189160a8f0dca8b90427bf690ea Mon Sep 17 00:00:00 2001 From: Roland McGrath Date: Fri, 7 Mar 2008 14:56:02 -0800 Subject: [PATCH] x86_64: make ptrace always sign-extend orig_ax to 64 bits This makes 64-bit ptrace calls setting the 64-bit orig_ax field for a 32-bit task sign-extend the low 32 bits up to 64. This matches what a 64-bit debugger expects when tracing a 32-bit task. This follows on my "x86_64 ia32 syscall restart fix". This didn't matter until that was fixed. The debugger ignores or zeros the high half of every register slot it sets (including the orig_rax pseudo-register) uniformly. It expects that the setting of the low 32 bits always has the same meaning as a 32-bit debugger setting those same 32 bits with native 32-bit facilities. This never arose before because the syscall restart check never matched any -ERESTART* values due to lack of sign extension. Before that fix, even 32-bit ptrace setting orig_eax to -1 failed to trigger the restart check anyway. So this was never noticed as a regression of 64-bit debuggers vs 32-bit debuggers on the same 64-bit kernel. Signed-off-by: Roland McGrath [ Changed to just do the sign-extension unconditionally on x86-64, since orig_ax is always just a small integer and doesn't need the full 64-bit range ] Signed-off-by: Linus Torvalds --- arch/x86/kernel/ptrace.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c index f41fdc98efb1..8f64abe699fd 100644 --- a/arch/x86/kernel/ptrace.c +++ b/arch/x86/kernel/ptrace.c @@ -323,6 +323,16 @@ static int putreg(struct task_struct *child, return set_flags(child, value); #ifdef CONFIG_X86_64 + /* + * Orig_ax is really just a flag with small positive and + * negative values, so make sure to always sign-extend it + * from 32 bits so that it works correctly regardless of + * whether we come from a 32-bit environment or not. + */ + case offsetof(struct user_regs_struct, orig_ax): + value = (long) (s32) value; + break; + case offsetof(struct user_regs_struct,fs_base): if (value >= TASK_SIZE_OF(child)) return -EIO; -- 2.20.1