On Fri, May 13, 2011 at 5:54 AM, Paolo Bonzini <bonz...@gnu.org> wrote: > On 05/13/2011 03:03 AM, Rong Xu wrote: >> >> * gcc/coverage.c (revision 173717): set a flag if building >> for Linux kernel. >> * gcc/tree-profile.c (revision 173717): don't emit TLS >> declarations for Linux kernel builds. > > I think this should be done without touching at all the profiling machinery > in GCC. > > 1) add a new TLS model -ftls-model=none and make the kernel uses it. The > model would simply force targetm.have_tls to false. >
This is a good idea. > 2) as Richi mentioned, gcov-io and libgcov changes then can move to the > kernel, and GCC needs no change at all here. > In fact -- reuse gcc code profiling machinery for FDO is the KEY objective in this effort --- the effort tries to minimize gcc changes by refactoring gcc code and isolating/abstracting away part of gcc implementation that is user space program specific without using runtime hooks. Aside from the kernel FDO change -- the refactoring itself actually makes the libgcov code more readable -- the existing implementation has many huge functions etc. Kernel source has their implementation of coverage testing -- but it makes lots of data structure assumptions and hard coded -- it can easily out of sync with gcc and is considered unmaintainable. Rong will have more explanation on the design. Thanks, David > BTW, these parts of LIPO: > >> + if (!is_kernel_build) >> + DECL_TLS_MODEL (dc_gcov_type_ptr_var) = >> + decl_default_tls_model (dc_gcov_type_ptr_var); >> >> dc_void_ptr_var = >> build_decl (UNKNOWN_LOCATION, VAR_DECL, >> @@ -1488,8 +1493,9 @@ >> ptr_void); >> DECL_ARTIFICIAL (dc_void_ptr_var) = 1; >> DECL_EXTERNAL (dc_void_ptr_var) = 1; >> - DECL_TLS_MODEL (dc_void_ptr_var) = >> - decl_default_tls_model (dc_void_ptr_var); >> + if (!is_kernel_build) >> + DECL_TLS_MODEL (dc_void_ptr_var) = >> + decl_default_tls_model (dc_void_ptr_var); > > Probably are missing a !targetm.have_tls. > > Paolo >
