[TargetLoweringObjectFileImpl] Produce .text.hot. instead of .text.hot for -fno-unique-section-names

GNU ld's internal linker script uses (https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=add44f8d5c5c05e08b11e033127a744d61c26aee)

  .text           :
  {
    *(.text.unlikely .text.*_unlikely .text.unlikely.*)
    *(.text.exit .text.exit.*)
    *(.text.startup .text.startup.*)
    *(.text.hot .text.hot.*)
    *(SORT(.text.sorted.*))
    *(.text .stub .text.* .gnu.linkonce.t.*)
    /* .gnu.warning sections are handled specially by elf.em.  */
    *(.gnu.warning)
  }

Because `*(.text.exit .text.exit.*)` is ordered before `*(.text .text.*)`, in a -ffunction-sections build, the C library function `exit` will be placed before other functions.
gold's `-z keep-text-section-prefix` has the same problem.

In lld, `-z keep-text-section-prefix` recognizes `.text.{exit,hot,startup,unlikely,unknown}.*`, but not `.text.{exit,hot,startup,unlikely,unknown}`, to avoid the strange placement problem.

In -fno-function-sections or -fno-unique-section-names mode, a function whose `function_section_prefix` is set to `.exit"`
will go to the output section `.text` instead of `.text.exit` when linked by lld.
To address the problem, append a dot to become `.text.exit.`

Reviewed By: grimar

Differential Revision: https://reviews.llvm.org/D79600

1 files changed, 6 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
index a9b1455..a3bfd65 100644
--- a/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringObjectFileImpl.cpp
@@ -611,15 +611,19 @@ getELFSectionNameForGlobal(const GlobalObject *GO, SectionKind Kind,
     Name = getSectionPrefixForGlobal(Kind);
   }
 
+  bool HasPrefix = false;
   if (const auto *F = dyn_cast<Function>(GO)) {
-    if (Optional<StringRef> Prefix = F->getSectionPrefix())
+    if (Optional<StringRef> Prefix = F->getSectionPrefix()) {
       Name += *Prefix;
+      HasPrefix = true;
+    }
   }
 
   if (UniqueSectionName) {
     Name.push_back('.');
     TM.getNameWithPrefix(Name, GO, Mang, /*MayAlwaysUsePrivate*/true);
-  }
+  } else if (HasPrefix)
+    Name.push_back('.');
   return Name;
 }