[llvm-readobj][test] - unwind.test: add comments, document the current behavior.

[grimar]

Summary

Here I've added comments, added testing for llvm-readelf and documented
the behavior that we already have.

It was discussed in the D80380 thread that we want to improve the
"p_memsz does not match p_filesz for GNU_EH_FRAME" message reported
(and probably convert error to a warning). This patch is a preparation
for that.

[jhenderson]

LGTM, with comment suggestions.

llvm/test/tools/llvm-readobj/ELF/unwind.test

208

Not related to this change, but yuck, this is horrible. Probably this wants implementing in yaml2obj at some point (perhaps wait until @Higuoxing has done work on .debug_frame support though). Same sort of comment applies ot the content of the .eh_frame_hdr though.

241

we partially dump the unwind information when

to a truncated -> to truncated

The line probably wants splitting in two.

[grimar]

llvm/test/tools/llvm-readobj/ELF/unwind.test

208

Perhaps it worth to implement ContentArray for such temporarily tests, like we discussed before in D75123.

llvm/test/tools/llvm-readobj/ELF/unwind.test

-# RUN: yaml2obj --docnum=1 %s -o %t1.exe
-# RUN: llvm-readobj --unwind %t1.exe | FileCheck %s
+## In this test we check how the unwind information is dumped with the use of --unwind.
+
+## First, check that both llvm-readobj and llvm-readelf are able to dump a valid unwind information.
+## Check that the output is the same for these tools.
+## The memory size of the PT_GNU_EH_FRAME equals its file size and they both are equal to 0x3c.
+## 0x3c is the size of the .eh_frame_hdr section.
+# RUN: yaml2obj --docnum=1 %s -DMEMSIZE=0x3c -DFILESIZE=0x3c -o %t1.valid
+# RUN: llvm-readobj --unwind %t1.valid | FileCheck %s
+# RUN: llvm-readelf --sections --unwind %t1.valid | FileCheck %s --check-prefixes=SIZE,CHECK
+
+## Validate the size of the .eh_frame_hdr section.
+# SIZE: [Nr] Name          Type     Address          Off    Size
+# SIZE: [ 2] .eh_frame_hdr PROGBITS 00000000004013c0 0000bc 00003c
 
 # CHECK:      EHFrameHeader {
 # CHECK-NEXT:  Address: 0x4013c0
 # CHECK-NEXT:  Offset: 0xbc
 # CHECK-NEXT:  Size: 0x3c
 # CHECK-NEXT:  Corresponding Section: .eh_frame_hdr
 # CHECK-NEXT:  Header {
 # CHECK-NEXT:    version: 1
- Name:            .eh_frame_hdr
     Address:         0x00000000004013c0
     AddressAlign:    4
     Content:         011B033B3C00000006000000E0F0FFFF8800000010F1FFFF58000000F6F1FFFFB000000010F2FFFFD000000090FEFFFF0001000000FFFFFF30010000
   - Name:            .eh_frame
     Type:            SHT_PROGBITS
     Flags:           [ SHF_ALLOC ]
     Address:         0x0000000000401400
     AddressAlign:    8
     Content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
 Symbols:
   - Name:            myfunc
     Type:            STT_FUNC
     Section:         .text
     Value:           0x0000000000400000
     Binding:         STB_GLOBAL
 ProgramHeaders:
-  - Type: PT_LOAD
-    Flags: [ PF_X, PF_R ]
-    VAddr: 0x00400000
-    PAddr: 0x00400000
+  - Type:     PT_LOAD
+    Flags:    [ PF_X, PF_R ]
+    VAddr:    0x00400000
+    PAddr:    0x00400000
     Sections:
       - Section: .text
   - Type: PT_GNU_EH_FRAME
     Flags: [ PF_X, PF_R ]
     VAddr: 0x004013C0
     PAddr: 0x004013C0
+    MemSize:  [[MEMSIZE]]
+    FileSize: [[FILESIZE]]
     Sections:
       - Section: .eh_frame_hdr
-...
+
+## Document we report a error when the memory size of the PT_GNU_EH_FRAME does not match its file size.
+## TODO: we want to report a warning and continue dumping instead.
+# RUN: yaml2obj --docnum=1 %s -DMEMSIZE=0x3b -DFILESIZE=0x3c -o %t1.size.mismatch
+# RUN: not llvm-readobj --unwind %t1.size.mismatch 2>&1 | \
+# RUN:   FileCheck -DFILE=%t1.size.mismatch %s --check-prefix=SIZE-MISMATCH
+# RUN: not llvm-readelf --unwind %t1.size.mismatch 2>&1 | \
+# RUN:   FileCheck -DFILE=%t1.size.mismatch %s --check-prefix=SIZE-MISMATCH
+
+# SIZE-MISMATCH: error: '[[FILE]]': p_memsz does not match p_filesz for GNU_EH_FRAME
+
+## Check we partially dump the unwind information when the PT_GNU_EH_FRAME segment
+## points to truncated data.
+# RUN: yaml2obj --docnum=1 %s -DMEMSIZE=0x1 -DFILESIZE=0x1 -o %t1.truncated
+# RUN: not llvm-readobj --unwind %t1.truncated 2>&1 | FileCheck -DFILE=%t1.truncated %s --check-prefix=TRUNCATED
+# RUN: not llvm-readelf --unwind %t1.truncated 2>&1 | FileCheck -DFILE=%t1.truncated %s --check-prefix=TRUNCATED
+
+# TRUNCATED:      EHFrameHeader {
+# TRUNCATED-NEXT:   Address: 0x4013c0
+# TRUNCATED-NEXT:   Offset: 0xbc
+# TRUNCATED-NEXT:   Size: 0x1
+# TRUNCATED-NEXT:   Corresponding Section: .eh_frame_hdr
+# TRUNCATED-NEXT:   Header {
+# TRUNCATED-NEXT:     version: 1
+# TRUNCATED-NEXT:     eh_frame_ptr_enc: 0x0
+# TRUNCATED-NEXT: error: '[[FILE]]': unexpected encoding eh_frame_ptr_enc
 
 ## Check we report an error when the tool is unable to parse .eh_frame section.
 # RUN: yaml2obj --docnum=2 %s -o %t2.exe
 # RUN: not llvm-readobj --unwind %t2.exe 2>&1 | FileCheck %s -DFILE=%t2.exe --check-prefix=NO-CIE-ERR
 
 # NO-CIE-ERR:      .eh_frame section at offset 0x40 address 0x0:
 # NO-CIE-ERR-NEXT: error: '[[FILE]]': parsing FDE data at 0x0 failed due to missing CIE
 # NO-CIE-ERR-NOT:  {{.}}