On Tue, Jul 05, 2005 at 02:31:15AM -0700, Roland McGrath wrote: > > When the 32-bit vDSO is used to make a system call, the %ebp register for > the 6th syscall arg has to be loaded from the user stack (where it's pushed > by the vDSO user code). The native i386 kernel always does this before > stopping for syscall tracing, so %ebp can be seen and modified via ptrace > to access the 6th syscall argument. The x86-64 kernel fails to do this, > presenting the stack address to ptrace instead. This makes the %rbp value > seen by 64-bit ptrace of a 32-bit process, and the %ebp value seen by a > 32-bit caller of ptrace, both differ from the native i386 behavior. > > This patch fixes the problem by putting the word loaded from the user stack > into %rbp before calling syscall_trace_enter, and reloading the 6th syscall > argument from there afterwards (so ptrace can change it). This makes the > behavior match that of i386 kernels.
Wouldn't this to botch a debugger which supported both backtracing and PTRACE_SYSCALL, when stopped in a syscall? We have unwind information for the VDSO and it's not going to tell us that the kernel has done something clever to the value of %ebp. -- Daniel Jacobowitz CodeSourcery, LLC - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
