Hi Andy, On 04/28/2016 02:53 PM, Andy Lutomirski wrote: > On 04/28/2016 08:18 AM, Christopher Covington wrote: >> Please take a look at the following prototype of sharing the PowerPC >> VDSO unmap and remap code with other architectures. I've only hooked >> up arm64 to begin with. If folks think this is a reasonable approach I >> can work on 32 bit ARM as well. Not hearing back from an earlier >> request for guidance [1], I simply dove in and started hacking. >> Laurent's test case [2][3] is a compelling illustration of whether VDSO >> remap works or not on a given architecture. > > I think there's a much nicer way: > > https://lkml.kernel.org/r/1461584223-9418-1-git-send-email-dsafonov@xxxxxxxxxxxxx > > Could arm64 and ppc use this approach? These arch_xyz hooks are gross. Thanks for the pointer. Any thoughts on how to keep essentially identical definitions of vdso_mremap from proliferating into every architecture and variant? > Also, at some point, possibly quite soon, x86 will want a way for > user code to ask the kernel to map a specific vdso variant at a specific > address. Could we perhaps add a new pair of syscalls: > > struct vdso_info { > unsigned long space_needed_before; > unsigned long space_needed_after; > unsigned long alignment; > }; > > long vdso_get_info(unsigned int vdso_type, struct vdso_info *info); > > long vdso_remap(unsigned int vdso_type, unsigned long addr, unsigned int flags); > > #define VDSO_X86_I386 0 > #define VDSO_X86_64 1 > #define VDSO_X86_X32 2 > // etc. > > vdso_remap will map the vdso of the chosen type such at > AT_SYSINFO_EHDR lines up with addr. It will use up to > space_needed_before bytes before that address and space_needed_after > after than address. It will also unmap the old vdso (or maybe only do > that if some flag is set). > > On x86, mremap is *not* sufficient for everything that's needed, > because some programs will need to change the vdso type. I don't I understand. Why can't people just exec() the ELF type that corresponds to the VDSO they want? Thanks, Cov -- Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
