Re: [Xen-devel] [PATCH for-4.13] clang: do not enable live-patching support

[Jan Beulich <jbeulich@xxxxxxxx>]

On 27.11.2019 17:01, Roger Pau Monne wrote:
> Live-patching requires unique symbols, and sadly the clang build
> generates a lot of duplicate symbols:
> 
> Duplicate symbol 'asid.c#get_cpu_info' (ffff82d0803032c0 != ffff82d0802e0f50)
> Duplicate symbol 'asid.c#get_cpu_info_from_stack' (ffff82d0802e1080 != 
> ffff82d0803032f0)
> Duplicate symbol 'ats.c#__list_add' (ffff82d080260a00 != ffff82d080267c70)
> Duplicate symbol 'boot.c#constant_test_bit' (ffff82d08040ea60 != 
> ffff82d0804372f0)
> Duplicate symbol 'common.c#clear_bit' (ffff82d080332440 != ffff82d0802d33b0)
> Duplicate symbol 'common.c#constant_test_bit' (ffff82d080332340 != 
> ffff82d0802d2220)
> Duplicate symbol 'common.c#cpumask_check' (ffff82d0802d3370 != 
> ffff82d080337b60)
> Duplicate symbol 'common.c#get_cpu_info' (ffff82d0802d22b0 != 
> ffff82d080331590)
> Duplicate symbol 'common.c#get_cpu_info_from_stack' (ffff82d0802d31c0 != 
> ffff82d0803374b0)
> Duplicate symbol 'common.c#pfn_to_pdx' (ffff82d0802d3270 != ffff82d080331e00)
> Duplicate symbol 'common.c#test_and_set_bit' (ffff82d0802d3360 != 
> ffff82d080332250)
> Duplicate symbol 'common.c#variable_clear_bit' (ffff82d0802d2270 != 
> ffff82d080337b50)
> Duplicate symbol 'compat.c#get_cpu_info' (ffff82d08026eab0 != 
> ffff82d080200460)
> Duplicate symbol 'compat.c#get_cpu_info_from_stack' (ffff82d08026ebd0 != 
> ffff82d080200f70)
> Duplicate symbol 'cpu_idle.c#get_cpu_info' (ffff82d0802ccb00 != 
> ffff82d08035fcc0)
> [...]
> 
> For the time being disable live-patching when building with clang,
> since duplicate symbols will trigger a build failure because
> ENFORCE_UNIQUE_SYMBOLS is now also enabled by default in conjunction
> with live-patching.
> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

To be honest, as indicated before I'm inclined to nak this patch
on the basis that a proper solution has been posted almost 3 weeks
ago (and this was already v2). Nevertheless a remark here:

> --- a/xen/common/Kconfig
> +++ b/xen/common/Kconfig
> @@ -80,6 +80,10 @@ config HAS_CHECKPOLICY
>       string
>       option env="XEN_HAS_CHECKPOLICY"
>  
> +config BUILD_WITH_CLANG
> +     string
> +     option env="XEN_BUILD_WITH_CLANG"

Instead of introducing a new option here, ...

> @@ -350,7 +354,7 @@ config CRYPTO
>  config LIVEPATCH
>       bool "Live patching support"
>       default X86
> -     depends on HAS_BUILD_ID = "y"
> +     depends on HAS_BUILD_ID = "y" && BUILD_WITH_CLANG != "y"

... seeing this, why don't you simply suppress HAS_BUILD_ID acquiring
a value of y in ./Config.mk (accompanied by a suitable comment)?

Jan

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