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Re: [Xen-devel] Ping: [PATCH] build: provide option to disambiguate symbol names
- To: Jan Beulich <jbeulich@xxxxxxxx>, Julien Grall <julien.grall@xxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, "Stefano Stabellini" <sstabellini@xxxxxxxxxx>, Konrad Wilk <konrad.wilk@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
- From: George Dunlap <george.dunlap@xxxxxxxxxx>
- Date: Thu, 7 Nov 2019 11:03:54 +0000
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- Cc: Juergen Gross <jgross@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 07 Nov 2019 11:04:11 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 11/7/19 7:20 AM, Jan Beulich wrote:
> On 24.10.2019 15:31, 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.
>>
>> Provide a Kconfig option to 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.
This is a good explanation, and I think the changes make sense. But
unfortunately...
>> 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.
...I don't follow this at all. What does the .file directive do in
those places, and why is it an issue? And why do we always disable it
in clang?
-George
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