This is the mail archive of the mailing list for the binutils project.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: Preventing preemption of 'protected' symbols in GNU ld 2.26

> On Mar 28, 2016, at 3:21 PM, Cary Coutant <> wrote:
>> Did you look at what the costs were in startup time and dirty pages by using
>> copy relocations? What do you do if the size of the definition changes in a
>> new version of the library?
> There wouldn't be a measurable cost in dirty pages; the copied objects
> are simply allocated in bss in the executable.

Wouldn't references to the symbol from within the .so need to be relocated to reference the now-canonical copy in the executable?


> Startup time wasn't a concern either, simply because COPY relocations
> weren't the real issue. We had to support an *occasional* COPY
> relocation in order to enable -fPIE to access globals directly rather
> than through the GOT. These would be the same COPY relocations that
> the apps would have already been using in non-PIE mode (things like
> stdin, stdout, and stderr, e.g.).
> The size of an object is baked into the ABI when a COPY relocation is
> used, so any change in size is an ABI change (often handled, as HJ
> pointed out, with versioning). For a lot of common COPY relocations,
> that's not really an issue, because both the size and the layout are
> baked in through macros like putc() and getc().
> -cary

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]