Re: [Xen-devel] [PATCH v2] build: provide option to disambiguate symbol names

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Fri, Nov 08, 2019 at 12:18:40PM +0100, Jan Beulich wrote:
> The .file assembler directives generated by the compiler do not include
> any path components (gcc) or just the ones specified on the command line
> (clang, at least version 5), and hence multiple identically named source
> files (in different directories) may produce identically named static
> symbols (in their kallsyms representation). The binary diffing algorithm
> used by xen-livepatch, however, depends on having unique symbols.
> 
> Make the ENFORCE_UNIQUE_SYMBOLS Kconfig option control the (build)
> behavior, and if enabled use objcopy to prepend the (relative to the
> xen/ subdirectory) path to the compiler invoked STT_FILE symbols. Note
> that this build option is made no longer depend on LIVEPATCH, but merely
> defaults to its setting now.
> 
> Conditionalize explicit .file directive insertion in C files where it
> exists just to disambiguate names in a less generic manner; note that
> at the same time the redundant emission of STT_FILE symbols gets
> suppressed for clang. Assembler files as well as multiply compiled C
> ones using __OBJECT_FILE__ are left alone for the time being.
> 
> Since we now expect there not to be any duplicates anymore, also don't
> force the selection of the option to 'n' anymore in allrandom.config.
> Similarly COVERAGE no longer suppresses duplicate symbol warnings if
> enforcement is in effect, which in turn allows
> SUPPRESS_DUPLICATE_SYMBOL_WARNINGS to simply depend on
> !ENFORCE_UNIQUE_SYMBOLS.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

And tested on FreeBSD with clang 8 and elftoolchain objcopy.

Thanks, Roger.

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