diff options
Diffstat (limited to 'devel/llvm60/files/lld/patch-head-r338251.diff')
| -rw-r--r-- | devel/llvm60/files/lld/patch-head-r338251.diff | 123 |
1 files changed, 0 insertions, 123 deletions
diff --git a/devel/llvm60/files/lld/patch-head-r338251.diff b/devel/llvm60/files/lld/patch-head-r338251.diff deleted file mode 100644 index 1c3df02100cd..000000000000 --- a/devel/llvm60/files/lld/patch-head-r338251.diff +++ /dev/null @@ -1,123 +0,0 @@ -r338251 | markj | 2018-08-23 16:58:19 +0200 (Thu, 23 Aug 2018) | 29 lines - -Add an lld option to emit PC-relative relocations for ifunc calls. - -The current kernel ifunc implementation creates a PLT entry for each -ifunc definition. ifunc calls therefore consist of a call to the -PLT entry followed by an indirect jump. The jump target is written -during boot when the kernel linker resolves R_[*]_IRELATIVE relocations. -This implementation is defined by requirements for userland code, where -text relocations are avoided. This requirement is not present for the -kernel, so the implementation has avoidable overhead (namely, an extra -indirect jump per call). - -Address this for now by adding a special option to the static linker -to inhibit PLT creation for ifuncs. Instead, relocations to ifunc call -sites are passed through to the output file, so the kernel linker can -enumerate such call sites and apply PC-relative relocations directly -to the text section. Thus the overhead of an ifunc call becomes exactly -the same as that of an ordinary function call. This option is only for -use by the kernel and will not work for regular programs. - -The final form of this optimization is up for debate; for now, this -change is simple and static enough to be acceptable as an interim -solution. - -Reviewed by: emaste -Discussed with: arichardson, dim -MFC after: 1 month -Sponsored by: The FreeBSD Foundation -Differential Revision: https://reviews.freebsd.org/D16748 - -Index: tools/lld/ELF/Config.h -=================================================================== ---- tools/lld/ELF/Config.h (revision 338250) -+++ tools/lld/ELF/Config.h (revision 338251) -@@ -155,6 +155,7 @@ struct Configuration { - bool ZCombreloc; - bool ZExecstack; - bool ZHazardplt; -+ bool ZIfuncnoplt; - bool ZNocopyreloc; - bool ZNodelete; - bool ZNodlopen; -Index: tools/lld/ELF/Driver.cpp -=================================================================== ---- tools/lld/ELF/Driver.cpp (revision 338250) -+++ tools/lld/ELF/Driver.cpp (revision 338251) -@@ -669,6 +669,7 @@ void LinkerDriver::readConfigs(opt::InputArgList & - Config->ZCombreloc = !hasZOption(Args, "nocombreloc"); - Config->ZExecstack = hasZOption(Args, "execstack"); - Config->ZHazardplt = hasZOption(Args, "hazardplt"); -+ Config->ZIfuncnoplt = hasZOption(Args, "ifunc-noplt"); - Config->ZNocopyreloc = hasZOption(Args, "nocopyreloc"); - Config->ZNodelete = hasZOption(Args, "nodelete"); - Config->ZNodlopen = hasZOption(Args, "nodlopen"); -Index: tools/lld/ELF/Relocations.cpp -=================================================================== ---- tools/lld/ELF/Relocations.cpp (revision 338250) -+++ tools/lld/ELF/Relocations.cpp (revision 338251) -@@ -374,6 +374,9 @@ static bool isStaticLinkTimeConstant(RelExpr E, Re - R_PPC_PLT_OPD, R_TLSDESC_CALL, R_TLSDESC_PAGE, R_HINT>(E)) - return true; - -+ if (Sym.isGnuIFunc() && Config->ZIfuncnoplt) -+ return false; -+ - // These never do, except if the entire file is position dependent or if - // only the low bits are used. - if (E == R_GOT || E == R_PLT || E == R_TLSDESC) -@@ -921,7 +924,9 @@ static void scanRelocs(InputSectionBase &Sec, Arra - // Strenghten or relax a PLT access. - // - // GNU ifunc symbols must be accessed via PLT because their addresses -- // are determined by runtime. -+ // are determined by runtime. If the -z ifunc-noplt option is specified, -+ // we permit the optimization of ifunc calls by omitting the PLT entry -+ // and preserving relocations at ifunc call sites. - // - // On the other hand, if we know that a PLT entry will be resolved within - // the same ELF module, we can skip PLT access and directly jump to the -@@ -929,7 +934,7 @@ static void scanRelocs(InputSectionBase &Sec, Arra - // all dynamic symbols that can be resolved within the executable will - // actually be resolved that way at runtime, because the main exectuable - // is always at the beginning of a search list. We can leverage that fact. -- if (Sym.isGnuIFunc()) -+ if (Sym.isGnuIFunc() && !Config->ZIfuncnoplt) - Expr = toPlt(Expr); - else if (!Preemptible && Expr == R_GOT_PC && !isAbsoluteValue(Sym)) - Expr = -@@ -1034,6 +1039,16 @@ static void scanRelocs(InputSectionBase &Sec, Arra - continue; - } - -+ // Preserve relocations against ifuncs if we were asked to do so. -+ if (Sym.isGnuIFunc() && Config->ZIfuncnoplt) { -+ if (Config->IsRela) -+ InX::RelaDyn->addReloc({Type, &Sec, Offset, false, &Sym, Addend}); -+ else -+ // Preserve the existing addend. -+ InX::RelaDyn->addReloc({Type, &Sec, Offset, false, &Sym, 0}); -+ continue; -+ } -+ - // If the output being produced is position independent, the final value - // is still not known. In that case we still need some help from the - // dynamic linker. We can however do better than just copying the incoming -Index: tools/lld/ELF/Writer.cpp -=================================================================== ---- tools/lld/ELF/Writer.cpp (revision 338250) -+++ tools/lld/ELF/Writer.cpp (revision 338251) -@@ -1400,8 +1400,11 @@ template <class ELFT> void Writer<ELFT>::finalizeS - applySynthetic({InX::EhFrame}, - [](SyntheticSection *SS) { SS->finalizeContents(); }); - -- for (Symbol *S : Symtab->getSymbols()) -+ for (Symbol *S : Symtab->getSymbols()) { - S->IsPreemptible |= computeIsPreemptible(*S); -+ if (S->isGnuIFunc() && Config->ZIfuncnoplt) -+ S->ExportDynamic = true; -+ } - - // Scan relocations. This must be done after every symbol is declared so that - // we can correctly decide if a dynamic relocation is needed. |