Change the warning message for -warn-ifunc-textrel.

[ruiu]

Summary

I don't think you can fix the issue by recompiling it without -fPIC
(is it?). This patch also change the man page description because that's
too detailed. Technical details of the glibc's bug should be noted in a
commit message, but that doesn't have to be written in a man page.

[emaste]

I don't think you can fix the issue by recompiling it without -fPIC

I would think a fix would be compiling with -fPIC.

lld/ELF/Relocations.cpp

991

I'm not sure about advice to link without -z text - that's the default, and so linking with or without it should have the same effect, disallowing text relocations?

[ruiu]

• update the warning message

[MaskRay]

lld/ELF/Relocations.cpp

991

I wonder if this option is still needed...

lld/ELF/Relocations.cpp

static void scanReloc(InputSectionBase &Sec, OffsetGetter &GetOffset, RelTy *&I,
   // 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
   // destination function. For example, if we are linking a main exectuable,
   // 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 (!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." +
+      warn("We detected that your program uses both ifunc symbols and text "
+           "relocations, which is not compatible with glibc released in 2018 "
+           "or earlier (version 2.28 or earlier) due to a bug in glibc. As a "
+           "result, your program may crash on startup on a system that uses "
+           "glibc as a libc (i.e. most Linux systems). If this applies to you, "
+           "consider recompiling with `-fPIC` or link your program without "
+           "`-z notext`. Use `-no-warn-ifunc-textrel` to disable this warning." +
            getLocation(Sec, Sym, Offset));
     }
     Expr = toPlt(Expr);
   } else if (!Sym.IsPreemptible && Expr == R_GOT_PC && !isAbsoluteValue(Sym)) {
     Expr = Target->adjustRelaxExpr(Type, RelocatedAddr, Expr);
   } else if (!Sym.IsPreemptible) {
     Expr = fromPlt(Expr);
   }

lld/docs/ld.lld.1

 .Ar file .
 .It Fl -warn-backrefs
 Warn about reverse or cyclic dependencies to or between static archives.
 This can be used to ensure linker invocation remains compatible with
 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.
+Warn if both ifunc symbols and text relocations are used. glibc
+released in 2018 or earlier (version 2.28 or earlier) has a bug that
+causes programs to crash on startup if both features are used.
 .It Fl -warn-unresolved-symbols
 Report unresolved symbols as warnings.
 .It Fl -whole-archive
 Force load of all members in a static library.
 .It Fl -wrap Ns = Ns Ar symbol
 Use wrapper functions for symbol.
 .It Fl z Ar option
 Linker option extensions.

lld/test/ELF/textrel.s

 # 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: We detected that your program uses both ifunc symbols and
 # 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