[llvm-dwarfdump] - Do not error out on R_X86_64_DTPOFF64/R_X86_64_DTPOFF32 relocations.

[grimar]

Summary

This is https://bugs.llvm.org/show_bug.cgi?id=39992,

If we have the following code (test.cpp):

thread_local int tdata = 24;

and build an .o file with debug information:

clang --target=x86_64-pc-linux -c bar.cpp -g

Then object produced may have R_X86_64_DTPOFF64/R_X86_64_DTPOFF32 relocations.
(clang emits R_X86_64_DTPOFF64 and gcc emits R_X86_64_DTPOFF32 for the code above for me)

Currently, llvm-dwarfdump fails to compute this TLS relocation when dumping object and reports an
error:
failed to compute relocation: R_X86_64_DTPOFF64, Invalid data was encountered while parsing the file

This relocation represents the offset in the TLS block and resolved by the linker, but this info is unavailable at the
point when the object file is dumped by this tool.

The patch adds the simple evaluation for such relocations to avoid emitting errors. Resulting behavior seems to
be equal to GNU dwarfdump, it dumps the locations without errors in the same way:

< 1><0x00000016>    DW_TAG_variable
                      DW_AT_name                  X
                      DW_AT_type                  <0x00000000>
                      DW_AT_external              yes(1)
                      DW_AT_location              len 0x000a: 0e0000000000000000e0: DW_OP_const8u 0 DW_OP_GNU_push_tls_address
< 1><0x0000002a>    DW_TAG_variable
                      DW_AT_name                  X
                      DW_AT_type                  <0x00000000>
                      DW_AT_external              yes(1)
                      DW_AT_location              len 0x0006: 0c00000000e0: DW_OP_const4u 0 DW_OP_GNU_push_tls_address

[grimar]

Note that if addends are involved, i.e. we have:

	.quad	tdata1 + 0x11@DTPOFF
...
	.long	tdata2 + 0x22@DTPOFF

Then GNU dwarfdump prints them:

LOCAL_SYMBOLS:
< 1><0x00000016>    DW_TAG_variable
                      DW_AT_name                  X
                      DW_AT_type                  <0x00000000>
                      DW_AT_external              yes(1)
                      DW_AT_location              len 0x000a: 0e1100000000000000e0: DW_OP_const8u 17 DW_OP_GNU_push_tls_address
< 1><0x0000002a>    DW_TAG_variable
                      DW_AT_name                  X
                      DW_AT_type                  <0x00000000>
                      DW_AT_external              yes(1)
                      DW_AT_location              len 0x0006: 0c22000000e0: DW_OP_const4u 34 DW_OP_GNU_push_tls_address

But llvm-dwarfdump don't. This might be a separate issue perhaps. I did not include addends into the test case.

[dblaikie]

Sounds alright to me - thanks!

include/llvm/Object/RelocVisitor.h

int64_t getELFAddend(RelocationRef R) {
     return *AddendOrErr;
   }
 
   uint64_t visitX86_64(uint32_t Rel, RelocationRef R, uint64_t Value) {
     switch (Rel) {
     case ELF::R_X86_64_NONE:
       return 0;
     case ELF::R_X86_64_64:
+    case ELF::R_X86_64_DTPOFF32:
+    case ELF::R_X86_64_DTPOFF64:
       return Value + getELFAddend(R);
     case ELF::R_X86_64_PC32:
       return Value + getELFAddend(R) - R.getOffset();
     case ELF::R_X86_64_32:
     case ELF::R_X86_64_32S:
       return (Value + getELFAddend(R)) & 0xFFFFFFFF;
     }
     HasError = true;

test/tools/llvm-dwarfdump/X86/debug_tls_relocs.s

+# RUN: llvm-mc %s -filetype obj -triple x86_64-pc-linux -o %t.o
+# RUN: llvm-dwarfdump -v %t.o | FileCheck %s
+
+# CHECK-NOT: error
+# CHECK: DW_AT_location [DW_FORM_exprloc] (DW_OP_const8u 0x0, DW_OP_GNU_push_tls_address)
+# CHECK: DW_AT_location [DW_FORM_exprloc] (DW_OP_const4u 0x0, DW_OP_GNU_push_tls_address)
+
+.section .debug_str,"MS",@progbits,1
+.Linfo_string0:
+ .asciz "X"
+
+.section .debug_abbrev,"",@progbits
+ .byte 1                # Abbreviation Code
+ .byte 17               # DW_TAG_compile_unit
+ .byte 1                # DW_CHILDREN_yes
+ .byte 37               # DW_AT_producer
+ .byte 14               # DW_FORM_strp
+ .byte 19               # DW_AT_language
+ .byte 5                # DW_FORM_data2
+
+ .byte 3                # DW_AT_name
+ .byte 14               # DW_FORM_strp
+ .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 73               # DW_AT_type
+ .byte 19               # DW_FORM_ref4
+ .byte 63               # DW_AT_external
+ .byte 25               # DW_FORM_flag_present
+
+ .byte 2                # DW_AT_location
+ .byte 24               # DW_FORM_exprloc
+ .byte 0                # EOM(1)
+ .byte 0                # EOM(2)
+
+ .byte 0                # EOM(3)
+
+.section .debug_info,"",@progbits
+ .long 49               # Length of Unit
+ .short 4               # DWARF version number
+ .long .debug_abbrev    # Offset Into Abbrev. Section
+ .byte 8                # Address Size (in bytes)
+ .byte 1                # Abbrev [1] 0xb:0x6c DW_TAG_compile_unit
+ .long .Linfo_string0   # DW_AT_producer
+ .short 4               # DW_AT_language
+ .long .Linfo_string0   # DW_AT_name
+                        
+ .byte 2                # Abbrev [2] 0x2a:0x16 DW_TAG_variable
+ .long .Linfo_string0   # DW_AT_name
+ .long 0                # DW_AT_type
+ .byte 10               # DW_AT_location
+ .byte 14
+ .quad tdata1@DTPOFF
+ .byte 224
+
+ .byte 2                # Abbrev [2] 0x47:0x16 DW_TAG_variable
+ .long .Linfo_string0   # DW_AT_name
+ .long 0                # DW_AT_type
+ .byte 6                # DW_AT_location
+ .byte 12
+ .long tdata2@DTPOFF
+ .byte 224
+
+ .byte 0                # End Of Children Mark
+ .byte 0                # End Of Children Mark