[PATCH] D27712: [ELF] - Do not crash when move location counter backward.

[George Rimar via Phabricator via llvm-commits]

grimar created this revision.
grimar added reviewers: ruiu, rafael.
grimar added subscribers: llvm-commits, evgeny777, grimar.

PR31335 shows that we do that in next case:
SECTIONS { .text 0x2000 : {. = 0x100 ; *(.text) } }

though documentations says that "If . is used inside a section description however, it refers to the byte offset from the start of that section, not an absolute address. " looks does not work as documented in bfd (as mentioned in comments for PR31335).
Until we find out the expected behavior was suggested at least not to 'crash', what we do after trying to generate huge file.


https://reviews.llvm.org/D27712

Files:
  ELF/LinkerScript.cpp
  test/ELF/linkerscript/locationcountererr.s


Index: test/ELF/linkerscript/locationcountererr.s
===================================================================
--- test/ELF/linkerscript/locationcountererr.s
+++ test/ELF/linkerscript/locationcountererr.s
@@ -0,0 +1,9 @@
+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: echo "SECTIONS { .text 0x2000 : {. = 0x10 ; *(.text) } }" > %t.script
+# RUN: not ld.lld %t --script %t.script -o %t1 2>&1 | FileCheck %s
+# CHECK: unable to move location counter backward for: .text
+
+.globl _start
+_start:
+nop
Index: ELF/LinkerScript.cpp
===================================================================
--- ELF/LinkerScript.cpp
+++ ELF/LinkerScript.cpp
@@ -464,7 +464,10 @@
   if (auto *AssignCmd = dyn_cast<SymbolAssignment>(&Base)) {
     if (AssignCmd->Name == ".") {
       // Update to location counter means update to section size.
-      Dot = AssignCmd->Expression(Dot);
+      uintX_t Val = AssignCmd->Expression(Dot);
+      if (Val < Dot)
+        error("unable to move location counter backward for: " + CurOutSec->Name);
+      Dot = Val;
       CurOutSec->Size = Dot - CurOutSec->Addr;
       return;
     }


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