Index: ELF/Config.h =================================================================== --- ELF/Config.h +++ ELF/Config.h @@ -176,6 +176,7 @@ bool UseAndroidRelrTags = false; bool WarnBackrefs; bool WarnCommon; + bool WarnIfuncTextrel; bool WarnMissingEntry; bool WarnSymbolOrdering; bool WriteAddends; Index: ELF/Driver.cpp =================================================================== --- ELF/Driver.cpp +++ ELF/Driver.cpp @@ -836,6 +836,8 @@ Config->WarnBackrefs = Args.hasFlag(OPT_warn_backrefs, OPT_no_warn_backrefs, false); Config->WarnCommon = Args.hasFlag(OPT_warn_common, OPT_no_warn_common, false); + Config->WarnIfuncTextrel = + Args.hasFlag(OPT_warn_ifunc_textrel, OPT_no_warn_ifunc_textrel, false); Config->WarnSymbolOrdering = Args.hasFlag(OPT_warn_symbol_ordering, OPT_no_warn_symbol_ordering, true); Config->ZCombreloc = getZFlag(Args, "combreloc", "nocombreloc", true); Index: ELF/Options.td =================================================================== --- ELF/Options.td +++ ELF/Options.td @@ -352,6 +352,10 @@ "Warn about duplicate common symbols", "Do not warn about duplicate common symbols (default)">; +defm warn_ifunc_textrel: B<"warn-ifunc-textrel", + "Warn about using ifunc symbols with text relocations", + "Do not warn about using ifunc symbols with text relocations (default)">; + defm warn_symbol_ordering: B<"warn-symbol-ordering", "Warn about problems with the symbol ordering file (default)", "Do not warn about problems with the symbol ordering file">; Index: ELF/Relocations.cpp =================================================================== --- ELF/Relocations.cpp +++ ELF/Relocations.cpp @@ -50,6 +50,7 @@ #include "SyntheticSections.h" #include "Target.h" #include "Thunks.h" +#include "lld/Common/ErrorHandler.h" #include "lld/Common/Memory.h" #include "lld/Common/Strings.h" #include "llvm/ADT/SmallSet.h" @@ -979,12 +980,22 @@ // 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()) { + if (!Config->ZText && Config->WarnIfuncTextrel) { + warn("using ifunc symbols when text relocations are allowed may produce " + "a binary that will segfault, if the object file is linked with " + "old version of glibc (glibc 2.28 and earlier). If this applies to " + "you, consider recompiling the object files without -fPIC and " + "without -Wl,-z,notext option. Use -no-warn-ifunc-textrel to " + "turn off this warning." + + getLocation(Sec, Sym, Offset)); + } Expr = toPlt(Expr); - else if (!Sym.IsPreemptible && Expr == R_GOT_PC && !isAbsoluteValue(Sym)) + } else if (!Sym.IsPreemptible && Expr == R_GOT_PC && !isAbsoluteValue(Sym)) { Expr = Target->adjustRelaxExpr(Type, RelocatedAddr, Expr); - else if (!Sym.IsPreemptible) + } else if (!Sym.IsPreemptible) { Expr = fromPlt(Expr); + } // This relocation does not require got entry, but it is relative to got and // needs it to be created. Here we request for that. Index: docs/ld.lld.1 =================================================================== --- docs/ld.lld.1 +++ docs/ld.lld.1 @@ -431,6 +431,17 @@ traditional Unix-like linkers. .It Fl -warn-common Warn about duplicate common symbols. +.It Fl -warn-ifunc-textrel +Warn about using ifunc symbols in conjunction with text relocations. +Older versions of glibc library (2.28 and earlier) has a bug that causes +the segment that includes ifunc symbols to be marked as not executable when +they are relocated. As a result, although the program compiles and links +successfully, it gives segmentation fault when the instruction pointer reaches +an ifunc symbol. Use -warn-ifunc-textrel to let lld give a warning, if the +code may include ifunc symbols, may do text relocations and be linked with +an older glibc version. Otherwise, there is no need to use it, as the default +value does not give a warning. This flag has been introduced in late 2018, +has no counter part in ld and gold linkers, and may be removed in the future. .It Fl -warn-unresolved-symbols Report unresolved symbols as warnings. .It Fl -whole-archive Index: test/ELF/textrel.s =================================================================== --- /dev/null +++ test/ELF/textrel.s @@ -0,0 +1,40 @@ +# REQUIRES: x86 +# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux-gnu %s -o %t.o + +# Without --warn-text-ifunc, lld should run fine: +# RUN: ld.lld -z notext %t.o -o %t2 + +# With --warn-text-ifunc, lld should run with warnings: +# RUN: ld.lld --warn-ifunc-textrel -z notext %t.o -o /dev/null 2>&1 | FileCheck %s +# CHECK: using ifunc symbols when text relocations are allowed may produce +# CHECK-SAME: a binary that will segfault, if the object file is linked with +# CHECK-SAME: old version of glibc (glibc 2.28 and earlier). If this applies to +# CHECK-SAME: you, consider recompiling the object files without -fPIC and +# CHECK-SAME: without -Wl,-z,notext option. Use -no-warn-ifunc-textrel to +# CHECK-SAME: turn off this warning. +# CHECK: >>> defined in {{.*}} +# CHECK: >>> referenced by {{.*}}:(.text+0x8) + +# Without text relocations, lld should run fine: +# RUN: ld.lld --fatal-warnings %t.o -o /dev/null + +.text +.globl a_func_impl +a_func_impl: + nop + +.globl selector +.type selector,@function +selector: + movl $a_func_impl, %eax + retq + +.globl a_func +.type a_func,@gnu_indirect_function +.set a_func, selector + +.globl _start +.type _start,@function +main: + callq a_func + retq