Re: [PATCH 5/5] x86/asm/entry/32: Simplify ptrace register shuffling

From: Ingo Molnar
Date: Thu Jun 18 2015 - 05:33:34 EST

* Denys Vlasenko <dvlasenk@xxxxxxxxxx> wrote:

> Before this patch, we were clearing pt_regs->r8..r11 on stack.
> We can as well just store actual r8..r11 registers there:
> they came from userspace, we leak no information by showing them to ptrace.
> This allows to get rid of one insn ("xor %eax,%eax").
> Not a big deal, but still...
> After call to syscall_trace_enter(), before this patch we were restoring
> clobbered registers and jump to code which converts 32-bit syscall
> ABI to 64-bit C ABI. This is unnecessary work, we can combine both
> steps into one (similar to what audit code does already).

So this really needs a description about what kind of testing was done, as
technically this changes the ABI. Heavy ptrace users should be tried: strace,
UML, etc.

I don't expect any problems, but still it needs to be tested.


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