[ELF] Mention section name for STT_SECTION in reportRangeError()

[MaskRay]

Summary

D73518 mentioned non-STT_SECTION symbol names. This patch extends the code to
handle STT_SECTION symbols, where we report the section name.
This change helps at least the following cases with very little code.

• Whether a out-of-range relocation is due to code or data.
• For a relocation in .debug_info, which referenced .debug_* section (due to DWARF32 limitation) causes the problem.

[dblaikie]

So this:

(.text+0x3): relocation R_X86_64_PC32 out of range: 2147483648 is not in [-2147483648, 2147483647]; references .bss+0

Says that we're trying to write into .text+0x3 (3 bytes into the .text section) the value 2147483648 as an offset, relative to .bss+0? (are there cases where the offset would be non-zero and the +N on the second part (the .bss+0) would be non-zero as well?)

The +0 on the .bss is the bit I find surprising/not sure I understand - I'd have thought it'd just be .bss & the +N is in the "N is not in [...];"?

[MaskRay]

In D145199#4165987, @dblaikie wrote:

So this:

(.text+0x3): relocation R_X86_64_PC32 out of range: 2147483648 is not in [-2147483648, 2147483647]; references .bss+0

Says that we're trying to write into .text+0x3 (3 bytes into the .text section) the value 2147483648 as an offset, relative to .bss+0? (are there cases where the offset would be non-zero and the +N on the second part (the .bss+0) would be non-zero as well?)

Yes.

The +0 on the .bss is the bit I find surprising/not sure I understand - I'd have thought it'd just be .bss & the +N is in the "N is not in [...];"?

A non-zero offset is possible. For example an C/C++ internal linkage function may have a non-zero offset relative to its section. A reference against the local symbol will be converted to a relocation against the section symbol.

[peter.smith]

Looks like a good improvement, one small suggestion on the text, but no strong opinion on it if you prefer the original.

lld/ELF/Relocations.cpp

106

One small suggestion, could use `"; references section " as that makes the +0 form a bit less surprising. I guess for cases like .text, .data etc. it will be obvious that it is a section symbol, but for some user defined names it might be less obvious.

[MaskRay]

remove offset (since it's always zero for the STT_SECTION symbol)

[dblaikie]

In D145199#4167966, @MaskRay wrote:

remove offset (since it's always zero for the STT_SECTION symbol)

Oh, nice!

lld/ELF/Relocations.cpp

if (!src.empty())
     msg += src + "\n>>>               ";
   return msg + s.getObjMsg(off);
 }
 
 void elf::reportRangeError(uint8_t *loc, const Relocation &rel, const Twine &v,
                            int64_t min, uint64_t max) {
   ErrorPlace errPlace = getErrorPlace(loc);
   std::string hint;
-  if (rel.sym && !rel.sym->isSection())
+  if (rel.sym) {
+    if (!rel.sym->isSection())
       hint = "; references " + lld::toString(*rel.sym);
+    else if (auto *d = dyn_cast<Defined>(rel.sym))
+      hint = ("; references section '" + d->section->name + "'").str();
+  }
   if (!errPlace.srcLoc.empty())
     hint += "\n>>> referenced by " + errPlace.srcLoc;
   if (rel.sym && !rel.sym->isSection())
     hint += getDefinedLocation(*rel.sym);
 
   if (errPlace.isec && errPlace.isec->name.startswith(".debug"))
     hint += "; consider recompiling with -fdebug-types-section to reduce size "
             "of debug sections";

lld/test/ELF/aarch64-movw-error.s

 movn x0, #:abs_g2_s:zero+0x1000000000000
 # CHECK: relocation R_AARCH64_MOVW_SABS_G0 out of range: -65537 is not in [-65536, 65535]
 movn x0, #:abs_g0_s:zero-0x10001
 # CHECK: relocation R_AARCH64_MOVW_SABS_G1 out of range: -4295032832 is not in [-4294967296, 4294967295]
 movn x0, #:abs_g1_s:zero-0x100010000
 # CHECK: relocation R_AARCH64_MOVW_SABS_G2 out of range: -281479271677952 is not in [-281474976710656, 281474976710655]
 movn x0, #:abs_g2_s:zero-0x1000100000000
 
-# CHECK: relocation R_AARCH64_MOVW_PREL_G0 out of range: 65536 is not in [-65536, 65535]
+# CHECK: relocation R_AARCH64_MOVW_PREL_G0 out of range: 65536 is not in [-65536, 65535]; references section '.text'
 movn x0, #:prel_g0:.+0x10000
 # CHECK: relocation R_AARCH64_MOVW_PREL_G1 out of range: 4294967296 is not in [-4294967296, 4294967295]
 movn x0, #:prel_g1:.+0x100000000
 # CHECK: relocation R_AARCH64_MOVW_PREL_G2 out of range: 281474976710656 is not in [-281474976710656, 281474976710655]
 movn x0, #:prel_g2:.+0x1000000000000
 # CHECK: relocation R_AARCH64_MOVW_PREL_G0 out of range: -65537 is not in [-65536, 65535]
 movn x0, #:prel_g0:.-0x10001
 # CHECK: relocation R_AARCH64_MOVW_PREL_G1 out of range: -4295032832 is not in [-4294967296, 4294967295]

lld/test/ELF/linkerscript/eh-frame-reloc-out-of-range.test

 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %p/Inputs/eh-frame-reloc-out-of-range.s -o %t.o
 # RUN: not ld.lld %t.o -T %s -o /dev/null 2>&1 | FileCheck %s
 
 PHDRS { eh PT_LOAD; text PT_LOAD; }
 SECTIONS { . = 0x10000;
   .eh_frame_hdr : { *(.eh_frame_hdr*) } : eh
   .eh_frame : { *(.eh_frame) } : eh
   . = 0xF00000000;
   .text : { *(.text*) } : text
 }
 
-# CHECK: error: {{.*}}:(.eh_frame+0x20): relocation R_X86_64_PC32 out of range: 64424443872 is not in [-2147483648, 2147483647]
+# CHECK: error: {{.*}}:(.eh_frame+0x20): relocation R_X86_64_PC32 out of range: 64424443872 is not in [-2147483648, 2147483647]; references section '.text'

lld/test/ELF/ppc64-reloc-pcrel34-overflow.s

 # REQUIRES: ppc
 # RUN: echo 'SECTIONS { \
 # RUN:   .text 0x10000: { *(.text) } \
 # RUN:   .data 0x200010000 : { *(.data) } \
 # RUN: }' > %t.script
 
 # RUN: llvm-mc -filetype=obj -triple=powerpc64le %s -o %t.o
 # RUN: not ld.lld -T %t.script %t.o -o /dev/null 2>&1 | FileCheck %s
 
 # RUN: llvm-mc -filetype=obj -triple=powerpc64 %s -o %t.o
 # RUN: not ld.lld -T %t.script %t.o -o /dev/null 2>&1 | FileCheck %s
 
-# CHECK: relocation R_PPC64_PCREL34 out of range: 8589934592 is not in [-8589934592, 8589934591]
+# CHECK: relocation R_PPC64_PCREL34 out of range: 8589934592 is not in [-8589934592, 8589934591]; references section '.data'
   plwa 3, glob_overflow@PCREL(0), 1
 
 # CHECK-NOT: relocation
   plwa 3, .data@PCREL(0), 1
 
 .data
 glob_overflow:
   .long 0
   .size glob_overflow, 4

lld/test/ELF/x86-64-reloc-range.s

 // REQUIRES: x86
 // RUN: llvm-mc %s -o %t.o -triple x86_64-pc-linux -filetype=obj
 // RUN: not ld.lld %t.o -o /dev/null -shared 2>&1 | FileCheck %s
 // RUN: ld.lld --noinhibit-exec -shared %t.o -o %t 2>&1 | FileCheck %s
 // RUN: ls %t
 
-// CHECK: {{.*}}:(.text+0x3): relocation R_X86_64_PC32 out of range: 2147483648 is not in [-2147483648, 2147483647]
+// CHECK: {{.*}}:(.text+0x3): relocation R_X86_64_PC32 out of range: 2147483648 is not in [-2147483648, 2147483647]; references section '.bss'
 // CHECK-NOT: relocation
 
         lea     foo(%rip), %rax
         lea     foo(%rip), %rax
 
         .hidden foo
         .bss
         .zero 0x7fffdf87
 foo: