On Fri, May 29, 2020 at 06:25:14PM -0300, Luis Machado wrote: > I have a question about siginfo MTE information. I suppose SEGV_MTESERR will > be the most useful setting for debugging, right? Does si_addr contain the > tagged pointer with the logical tag, a zero-tagged memory address or a > tagged pointer with the allocation tag? The si_addr is zero-tagged currently. We were planning to expose the tag in FAR_EL1 as a separate siginfo field. See these discussions: https://lore.kernel.org/linux-arm-kernel/20200513180914.50892-1-pcc@xxxxxxxxxx/ https://lore.kernel.org/linux-arm-kernel/20200521022943.195898-1-pcc@xxxxxxxxxx/ In theory, we could add the tag to si_addr for SEGV_MTESERR, it shouldn't break the existing ABI (well, it depends on how you look at it). > From the debugger user's perspective, one would want to see both the logical > tag and the allocation tag. And it would be handy to have both available in > siginfo. Does that make sense? The debugger can access the allocation tag via PTRACE_PEEKMTETAGS. I don't think the kernel should provide this in siginfo. Also, the signal handler can do an LDG and read the allocation tag directly, no need for it to be in siginfo. > Also, when would we see SEGV_MTEAERR, for example? That would provide no > additional information about a particular memory address, which is not that > useful for the debugger. Yeah, we can't really do much here since the hardware doesn't provide us such information. The async mode is only useful as a general test to see if your program has MTE faults but for actual debugging you'd have to switch to synchronous. For glibc at least, I think the mode can be driven by an environment variable. -- Catalin
