[PATCH] D44205: [ELF] Prevent crash when reporting error messages if debug line cannot be parsed

[James Henderson via Phabricator via llvm-commits]

jhenderson created this revision.
jhenderson added reviewers: espindola, ruiu, grimar.
Herald added subscribers: JDevlieghere, arichardson, aprantl, emaste.

I noticed this whilst doing some work on the debug line parser. LLD uses the debug info and debug line sections to determine the location of e.g. references to undefined symbols, when producing error messages. In the event that debug info was present, but debug line parsing failed for some reason, then a nullptr would end up being dereferenced by the location-lookup code.


Repository:
  rLLD LLVM Linker

https://reviews.llvm.org/D44205

Files:
  ELF/InputFiles.cpp
  test/ELF/Inputs/undef-bad-debug.s
  test/ELF/undef.s


Index: test/ELF/undef.s
===================================================================
--- test/ELF/undef.s
+++ test/ELF/undef.s
@@ -2,9 +2,10 @@
 # RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %s -o %t.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %p/Inputs/undef.s -o %t2.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %p/Inputs/undef-debug.s -o %t3.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-pc-linux %p/Inputs/undef-bad-debug.s -o %t4.o
 # RUN: llvm-ar rc %t2.a %t2.o
-# RUN: not ld.lld %t.o %t2.a %t3.o -o %t.exe 2>&1 | FileCheck %s
-# RUN: not ld.lld -pie %t.o %t2.a %t3.o -o %t.exe 2>&1 | FileCheck %s
+# RUN: not ld.lld %t.o %t2.a %t3.o %t4.o -o %t.exe 2>&1 | FileCheck %s
+# RUN: not ld.lld -pie %t.o %t2.a %t3.o %t4.o -o %t.exe 2>&1 | FileCheck %s
 
 # CHECK: error: undefined symbol: foo
 # CHECK: >>> referenced by undef.s
@@ -33,6 +34,9 @@
 # CHECK: >>> referenced by undef-debug.s:11 (dir{{/|\\}}undef-debug.s:11)
 # CHECK: >>>               {{.*}}.o:(.text.2+0x0)
 
+# CHECK: error: undefined symbol: zed6
+# CHECK: >>> referenced by {{.*}}tmp4.o:(.text+0x0)
+
 # RUN: not ld.lld %t.o %t2.a -o %t.exe -no-demangle 2>&1 | \
 # RUN:   FileCheck -check-prefix=NO-DEMANGLE %s
 # NO-DEMANGLE: error: undefined symbol: _Z3fooi
Index: test/ELF/Inputs/undef-bad-debug.s
===================================================================
--- test/ELF/Inputs/undef-bad-debug.s
+++ test/ELF/Inputs/undef-bad-debug.s
@@ -0,0 +1,44 @@
+.section .text,"ax"
+sym:
+    .quad zed6
+    
+.section .debug_info,"", at progbits
+    .long   .Lcu_end - .Lcu_start   # Length of Unit
+.Lcu_start:
+    .short  4                       # DWARF version number
+    .long   .Lsection_abbrev        # Offset Into Abbrev. Section
+    .byte   8                       # Address Size (in bytes)
+    .byte   1                       # Abbrev [1] 0xb:0x79 DW_TAG_compile_unit
+    .byte   2                       # Abbrev [2] 0x2a:0x15 DW_TAG_variable
+    .long   .Linfo_string           # DW_AT_name
+                                        # DW_AT_external
+    .byte   1                       # DW_AT_decl_file
+    .byte   3                       # DW_AT_decl_line
+    .byte   0                       # End Of Children Mark
+.Lcu_end:
+
+.section .debug_abbrev,"", at progbits
+.Lsection_abbrev:
+    .byte   1                       # Abbreviation Code
+    .byte   17                      # DW_TAG_compile_unit
+    .byte   1                       # DW_CHILDREN_yes
+    .byte   0                       # EOM(1)
+    .byte   0                       # EOM(2)
+    .byte   2                       # Abbreviation Code
+    .byte   52                      # DW_TAG_variable
+    .byte   0                       # DW_CHILDREN_no
+    .byte   3                       # DW_AT_name
+    .byte   14                      # DW_FORM_strp
+    .byte   63                      # DW_AT_external
+    .byte   25                      # DW_FORM_flag_present
+    .byte   58                      # DW_AT_decl_file
+    .byte   11                      # DW_FORM_data1
+    .byte   59                      # DW_AT_decl_line
+    .byte   11                      # DW_FORM_data1
+    .byte   0                       # EOM(1)
+    .byte   0                       # EOM(2)
+    .byte   0                       # EOM(3)
+
+.section .debug_str,"MS", at progbits,1
+.Linfo_string:
+    .asciz "sym"
Index: ELF/InputFiles.cpp
===================================================================
--- ELF/InputFiles.cpp
+++ ELF/InputFiles.cpp
@@ -146,7 +146,7 @@
 
     // Get the source filename index for the variable.
     unsigned File = dwarf::toUnsigned(Die.find(dwarf::DW_AT_decl_file), 0);
-    if (!LT->hasFileAtIndex(File))
+    if (!LT || !LT->hasFileAtIndex(File))
       continue;
 
     // Get the line number on which the variable is declared.


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