Will, On 15 January 2014 12:07, Will Deacon <[email protected]> wrote: > On Wed, Jan 15, 2014 at 10:30:48AM +0000, Jean Pihet wrote: >> Hi Will, > > Hi Jean, > >> On 6 January 2014 19:30, Will Deacon <[email protected]> wrote: >> > On Mon, Dec 30, 2013 at 04:25:30PM +0000, Jean Pihet wrote: >> >> From: Jean Pihet <[email protected]> >> >> >> >> This patch implements the functions required for the perf registers API, >> >> allowing the perf tool to interface kernel register dumps with libunwind >> >> in order to provide userspace backtracing. >> >> Compat mode is also supported. >> > >> > [...] >> > >> >> +u64 perf_reg_value(struct pt_regs *regs, int idx) >> >> +{ >> >> + if (WARN_ON_ONCE((u32)idx >= PERF_REG_ARM64_MAX)) >> >> + return 0; >> > >> > While this is probably fine, I'd feel more comfortable if you had separate >> > limit checks for native and compat... >> In fact in the native and compat modes the same set of registers are >> accessed, based on the native regs that are registered to the perf >> event core, cf. the definition of PERF_REGS_MASK in >> tools/perf/arch/arm64/include/perf_regs.h. >> >> The regs set could be registered differently based on the binary to >> trace, but unfortunately the perf core code does not allow that. >> >> I would leave the code as is, what do you think? > > Well, what business would a compat task have accessing registers beyond the > compat subset? Since we don't expose the PC, we can simply lower the limit > as the compat registers form a prefix of the native registers, no? Yes it is a good thing to clamp the range of registers, based on the compat mode. Unfortunately the perf core code does not handle the compat mode, instead it always accesses all _native_ registers.
Here is the proposal (after our discussion on IRC): - use the current patches on ARM64 so that we have a working solution that one can test/stress/use on real workloads, - re-factor the perf core code later to make able to handle multiple ABIs and corresponding registers sets. Are you ok with that? Regards, Jean > > Will -- 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/
