| Message ID | 20190410134517.63896-1-bruce.richardson@intel.com |
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| Headers | show |
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Hello, On Wed, Apr 10, 2019 at 3:45 PM Bruce Richardson <bruce.richardson@intel.com> wrote: > Weak functions don't work well with static library builds as the linker > always picks the first version of a function irrespective of whether it is > weak or not. The solution to this is to use the "whole-archive" flag when > linking, but this has the nasty side-effect that it causes the resulting > binary to be larger than it needs to be. > > > A further problem with this approach of using "whole-archive" is that one > either needs to link all libraries with this flag or track what libraries > need it or not - the latter being especially a problem for apps not using > the DPDK build system itself (i.e. most apps not shipped with DPDK itself). > For meson builds this information needs to make its way all the way through > to the pkgconfig file generated - not a trivial undertaking. > > Thankfully, though, the use of weak functions is limited to use for > multiple functions within a single library, meaning that when the lib is > being built, the build system itself can know whether the "weak" function > is needed or not. This allows us to change the weak function to a > conditionally compiled regular function used in fallback case. This makes > the need for "whole-archive" flag, and any special linking measures for the > library, go away. > > [This set does not touch the drivers, only the libraries, since there are > other special linker flags needed for drivers in general, making the > problem less severe for driver .a files.] > > Was there something preventing this patchset from getting merged ?
On Mon, May 27, 2019 at 04:13:53PM +0200, David Marchand wrote: > Hello, > On Wed, Apr 10, 2019 at 3:45 PM Bruce Richardson > <[1]bruce.richardson@intel.com> wrote: > > Weak functions don't work well with static library builds as the > linker > always picks the first version of a function irrespective of whether > it is > weak or not. The solution to this is to use the "whole-archive" flag > when > linking, but this has the nasty side-effect that it causes the > resulting > binary to be larger than it needs to be. > A further problem with this approach of using "whole-archive" is > that one > either needs to link all libraries with this flag or track what > libraries > need it or not - the latter being especially a problem for apps not > using > the DPDK build system itself (i.e. most apps not shipped with DPDK > itself). > For meson builds this information needs to make its way all the way > through > to the pkgconfig file generated - not a trivial undertaking. > Thankfully, though, the use of weak functions is limited to use for > multiple functions within a single library, meaning that when the > lib is > being built, the build system itself can know whether the "weak" > function > is needed or not. This allows us to change the weak function to a > conditionally compiled regular function used in fallback case. This > makes > the need for "whole-archive" flag, and any special linking measures > for the > library, go away. > [This set does not touch the drivers, only the libraries, since > there are > other special linker flags needed for drivers in general, making the > problem less severe for driver .a files.] > > Was there something preventing this patchset from getting merged ? > -- > David Marchand > I believe Aaron Conole had some changes in the same area and was looking to roll these changes into a bigger patchset of his. Aaron, can you please confirm? /Bruce
Bruce Richardson <bruce.richardson@intel.com> writes: > On Mon, May 27, 2019 at 04:13:53PM +0200, David Marchand wrote: >> Hello, >> On Wed, Apr 10, 2019 at 3:45 PM Bruce Richardson >> <[1]bruce.richardson@intel.com> wrote: >> >> Weak functions don't work well with static library builds as the >> linker >> always picks the first version of a function irrespective of whether >> it is >> weak or not. The solution to this is to use the "whole-archive" flag >> when >> linking, but this has the nasty side-effect that it causes the >> resulting >> binary to be larger than it needs to be. >> A further problem with this approach of using "whole-archive" is >> that one >> either needs to link all libraries with this flag or track what >> libraries >> need it or not - the latter being especially a problem for apps not >> using >> the DPDK build system itself (i.e. most apps not shipped with DPDK >> itself). >> For meson builds this information needs to make its way all the way >> through >> to the pkgconfig file generated - not a trivial undertaking. >> Thankfully, though, the use of weak functions is limited to use for >> multiple functions within a single library, meaning that when the >> lib is >> being built, the build system itself can know whether the "weak" >> function >> is needed or not. This allows us to change the weak function to a >> conditionally compiled regular function used in fallback case. This >> makes >> the need for "whole-archive" flag, and any special linking measures >> for the >> library, go away. >> [This set does not touch the drivers, only the libraries, since >> there are >> other special linker flags needed for drivers in general, making the >> problem less severe for driver .a files.] >> >> Was there something preventing this patchset from getting merged ? >> -- >> David Marchand >> > I believe Aaron Conole had some changes in the same area and was looking to > roll these changes into a bigger patchset of his. Aaron, can you please > confirm? Yes - Sorry the patches are in my queue. Maybe it just makes sense to merge these though? > /Bruce
On Mon, May 27, 2019 at 04:57:15PM -0400, Aaron Conole wrote: > Bruce Richardson <bruce.richardson@intel.com> writes: > > > On Mon, May 27, 2019 at 04:13:53PM +0200, David Marchand wrote: > >> Hello, > >> On Wed, Apr 10, 2019 at 3:45 PM Bruce Richardson > >> <[1]bruce.richardson@intel.com> wrote: > >> > >> Weak functions don't work well with static library builds as the > >> linker > >> always picks the first version of a function irrespective of whether > >> it is > >> weak or not. The solution to this is to use the "whole-archive" flag > >> when > >> linking, but this has the nasty side-effect that it causes the > >> resulting > >> binary to be larger than it needs to be. > >> A further problem with this approach of using "whole-archive" is > >> that one > >> either needs to link all libraries with this flag or track what > >> libraries > >> need it or not - the latter being especially a problem for apps not > >> using > >> the DPDK build system itself (i.e. most apps not shipped with DPDK > >> itself). > >> For meson builds this information needs to make its way all the way > >> through > >> to the pkgconfig file generated - not a trivial undertaking. > >> Thankfully, though, the use of weak functions is limited to use for > >> multiple functions within a single library, meaning that when the > >> lib is > >> being built, the build system itself can know whether the "weak" > >> function > >> is needed or not. This allows us to change the weak function to a > >> conditionally compiled regular function used in fallback case. This > >> makes > >> the need for "whole-archive" flag, and any special linking measures > >> for the > >> library, go away. > >> [This set does not touch the drivers, only the libraries, since > >> there are > >> other special linker flags needed for drivers in general, making the > >> problem less severe for driver .a files.] > >> > >> Was there something preventing this patchset from getting merged ? > >> -- > >> David Marchand > >> > > I believe Aaron Conole had some changes in the same area and was looking to > > roll these changes into a bigger patchset of his. Aaron, can you please > > confirm? > > Yes - Sorry the patches are in my queue. Maybe it just makes sense to > merge these though? > Funnily enough, I've no objections to that :-)
10/04/2019 15:45, Bruce Richardson: > Weak functions don't work well with static library builds as the linker > always picks the first version of a function irrespective of whether it is > weak or not. The solution to this is to use the "whole-archive" flag when > linking, but this has the nasty side-effect that it causes the resulting > binary to be larger than it needs to be. > > > A further problem with this approach of using "whole-archive" is that one > either needs to link all libraries with this flag or track what libraries > need it or not - the latter being especially a problem for apps not using > the DPDK build system itself (i.e. most apps not shipped with DPDK itself). > For meson builds this information needs to make its way all the way through > to the pkgconfig file generated - not a trivial undertaking. > > Thankfully, though, the use of weak functions is limited to use for > multiple functions within a single library, meaning that when the lib is > being built, the build system itself can know whether the "weak" function > is needed or not. This allows us to change the weak function to a > conditionally compiled regular function used in fallback case. This makes > the need for "whole-archive" flag, and any special linking measures for the > library, go away. > > [This set does not touch the drivers, only the libraries, since there are > other special linker flags needed for drivers in general, making the > problem less severe for driver .a files.] > > Bruce Richardson (2): > acl: remove use of weak functions > bpf: remove use of weak functions Applied, thanks