[lld] 025b309 - Revert D126950 "[lld][WebAssembly] Retain data segments referenced via __start/__stop"

[Fangrui Song via llvm-commits]

Author: Fangrui Song
Date: 2022-06-03T22:18:06-07:00
New Revision: 025b309631e996f48b8367a7a2fa1032fa04a77c

URL: https://github.com/llvm/llvm-project/commit/025b309631e996f48b8367a7a2fa1032fa04a77c
DIFF: https://github.com/llvm/llvm-project/commit/025b309631e996f48b8367a7a2fa1032fa04a77c.diff

LOG: Revert D126950 "[lld][WebAssembly] Retain data segments referenced via __start/__stop"

This reverts commit dcf3368e33c3a01bd21b692d3be5dc1ecee587f4.

It breaks -DLLVM_ENABLE_ASSERTIONS=on builds. In addition, the description is
incorrect about ld.lld behavior. For wasm, there should be justification to add
the new mode.

Added: 
    

Modified: 
    lld/wasm/MarkLive.cpp

Removed: 
    lld/test/wasm/gc-sections-startstop.s


################################################################################
diff  --git a/lld/test/wasm/gc-sections-startstop.s b/lld/test/wasm/gc-sections-startstop.s
deleted file mode 100644
index f90164d743a9c..0000000000000
--- a/lld/test/wasm/gc-sections-startstop.s
+++ /dev/null
@@ -1,89 +0,0 @@
-# RUN: llvm-mc -triple=wasm32-unknown-unknown -filetype=obj -o %t.o %s
-# RUN: wasm-ld %t.o -o %t.wasm
-# RUN: llvm-objdump -d --no-show-raw-insn %t.wasm | FileCheck %s
-
-# FOO_MD symbol is not used directly, but is referenced through __start/__stop_foo_md
-foo_md_size:
-	.functype	foo_md_size () -> (i32)
-	i32.const	__stop_foo_md
-	i32.const	__start_foo_md
-	i32.sub
-	end_function
-
-# CHECK: <foo_md_size>:
-# CHECK-EMPTY:
-# CHECK-NEXT: i32.const [[#STOP_ADDR:]]
-# CHECK-NEXT: i32.const [[#STOP_ADDR - 4]]
-# CHECK-NEXT: i32.sub
-
-# All segments in concat_section section are marked as live.
-concat_section_size:
-	.functype	concat_section_size () -> (i32)
-	i32.const	__stop_concat_section
-	i32.const	__start_concat_section
-	i32.sub
-	end_function
-
-# CHECK: <concat_section_size>:
-# CHECK-EMPTY:
-# CHECK-NEXT: i32.const [[#STOP_ADDR:]]
-# CHECK-NEXT: i32.const [[#STOP_ADDR - 8]]
-# CHECK-NEXT: i32.sub
-
-
-# __start/__stop symbols don't retain invalid C name sections
-invalid_name_section_size:
-	.functype	invalid_name_section_size () -> (i32)
-	i32.const	__stop_invalid.dot.name
-	i32.const	__start_invalid.dot.name
-	i32.sub
-	end_function
-
-# CHECK: <invalid_name_section_size>:
-# CHECK-EMPTY:
-# CHECK-NEXT: i32.const 0
-# CHECK-NEXT: i32.const 0
-# CHECK-NEXT: i32.sub
-
-
-	.globl	_start
-_start:
-	.functype	_start () -> ()
-	call	foo_md_size
-	drop
-	call	concat_section_size
-	drop
-	call	invalid_name_section_size
-	drop
-	end_function
-
-
-	.section	foo_md,"",@
-FOO_MD:
-	.asciz	"bar"
-	.size	FOO_MD, 4
-
-	.size	__start_foo_md, 4
-	.size	__stop_foo_md, 4
-
-
-	.section	concat_section,"",@
-concat_segment_1:
-	.asciz	"xxx"
-	.size	concat_segment_1, 4
-
-concat_segment_2:
-	.asciz	"yyy"
-	.size	concat_segment_2, 4
-
-	.size	__start_concat_section, 4
-	.size	__stop_concat_section, 4
-
-
-	.section	invalid.dot.name,"",@
-invalid_name_section:
-	.asciz	"fizz"
-	.size	invalid_name_section, 5
-
-	.weak	__start_invalid.dot.name
-	.weak	__stop_invalid.dot.name

diff  --git a/lld/wasm/MarkLive.cpp b/lld/wasm/MarkLive.cpp
index c811dd4d2226b..3e5d234eeccc0 100644
--- a/lld/wasm/MarkLive.cpp
+++ b/lld/wasm/MarkLive.cpp
@@ -24,7 +24,6 @@
 #include "InputElement.h"
 #include "SymbolTable.h"
 #include "Symbols.h"
-#include "lld/Common/Strings.h"
 
 #define DEBUG_TYPE "lld"
 
@@ -42,7 +41,6 @@ class MarkLive {
 
 private:
   void enqueue(Symbol *sym);
-  void enqueue(InputChunk *chunk);
   void enqueueInitFunctions(const ObjFile *sym);
   void mark();
   bool isCallCtorsLive();
@@ -86,12 +84,6 @@ void MarkLive::enqueueInitFunctions(const ObjFile *obj) {
   }
 }
 
-void MarkLive::enqueue(InputChunk *chunk) {
-  LLVM_DEBUG(dbgs() << "markLive: " << chunk->getName() << "\n");
-  chunk->live = true;
-  queue.push_back(chunk);
-}
-
 void MarkLive::run() {
   // Add GC root symbols.
   if (!config->entry.empty())
@@ -105,24 +97,10 @@ void MarkLive::run() {
   if (WasmSym::callDtors)
     enqueue(WasmSym::callDtors);
 
-  for (const ObjFile *obj : symtab->objectFiles) {
-    if (!obj->isLive()) {
-      continue;
-    }
-    // Enqueue constructors in objects explicitly live from the command-line.
-    enqueueInitFunctions(obj);
-
-    // Enqueue data segments referenced through __start/__stop symbols.
-    for (InputChunk *segment : obj->segments) {
-      auto name = segment->name;
-      if (!isValidCIdentifier(name))
-        continue;
-      if (symtab->find(("__start_" + name).str()) ||
-          symtab->find(("__stop_" + name).str())) {
-        enqueue(segment);
-      }
-    }
-  }
+  // Enqueue constructors in objects explicitly live from the command-line.
+  for (const ObjFile *obj : symtab->objectFiles)
+    if (obj->isLive())
+      enqueueInitFunctions(obj);
 
   mark();