[lld][ELF] Do not emit warning for NOLOAD output sections

Much of NOLOAD's intended use is to explicitly change the type of an
output section, so we shouldn't flag these as warnings.

Differential Revision: https://reviews.llvm.org/D151144

lld/ELF/OutputSections.cpp

@@ -116,16 +116,18 @@ void OutputSection::commitSection(InputSection *isec) {
     if (hasInputSections || typeIsSet) {
       if (typeIsSet || !canMergeToProgbits(type) ||
           !canMergeToProgbits(isec->type)) {
-        // Changing the type of a (NOLOAD) section is fishy, but some projects
-        // (e.g. https://github.com/ClangBuiltLinux/linux/issues/1597)
-        // traditionally rely on the behavior. Issue a warning to not break
-        // them. Other types get an error.
-        auto diagnose = type == SHT_NOBITS ? warn : errorOrWarn;
-        diagnose("section type mismatch for " + isec->name + "\n>>> " +
-                 toString(isec) + ": " +
-                 getELFSectionTypeName(config->emachine, isec->type) +
-                 "\n>>> output section " + name + ": " +
-                 getELFSectionTypeName(config->emachine, type));
+        // The (NOLOAD) changes the section type to SHT_NOBITS, the intention is
+        // that the contents at that address is provided by some other means.
+        // Some projects (e.g.
+        // https://github.com/ClangBuiltLinux/linux/issues/1597) rely on the
+        // behavior. Other types get an error.
+        if (type != SHT_NOBITS) {
+          errorOrWarn("section type mismatch for " + isec->name + "\n>>> " +
+                      toString(isec) + ": " +
+                      getELFSectionTypeName(config->emachine, isec->type) +
+                      "\n>>> output section " + name + ": " +
+                      getELFSectionTypeName(config->emachine, type));
+        }
       }
       if (!typeIsSet)
         type = SHT_PROGBITS;

lld/test/ELF/linkerscript/noload.s

@@ -19,10 +19,10 @@
 
 ## The output SHT_PROBITS is contrary to the user expectation of SHT_NOBITS.
 ## Issue a warning. See https://github.com/ClangBuiltLinux/linux/issues/1597
-# RUN: ld.lld --script %t/lds %t.o %t/mismatch.o -o %t/out 2>&1 | FileCheck %s --check-prefix=WARN
+# RUN: ld.lld --script %t/lds %t.o %t/mismatch.o -o %t/out 2>&1 | FileCheck %s --check-prefix=WARN --allow-empty
 # RUN: llvm-readelf -S -l %t/out | FileCheck %s --check-prefix=CHECK2
 
-# WARN:   warning: section type mismatch for .data_noload_a
+# WARN-NOT:   warning:
 # CHECK2:      Name                 Type     Address          Off               Size
 # CHECK2:      .data_noload_a       NOBITS   0000000000000000 [[OFF:[0-9a-f]+]] 001001
 
@@ -45,5 +45,8 @@ SECTIONS {
   .data_noload_a (NOLOAD) : { *(.data_noload_a) }
   .data_noload_b (0x10000) (NOLOAD) : { *(.data_noload_b) }
   .no_input_sec_noload (NOLOAD) : { . += 1; }
-  .text (0x20000) : { *(.text) }
+  .text (0x20000) : {
+    *(.text);
+    _start = .;
+  }
 }