[llvm] [llvm-objdump][ELF]Fix crash when reading strings from .dynstr (PR #125679)

[James Henderson via llvm-commits]

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@@ -470,3 +473,34 @@ Sections:
        Value: 0x1
      - Tag:   DT_NULL
        Value: 0x0
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_EXEC
+  Machine: EM_X86_64
+Sections:
+  - Name:    .dynstr
+    Type:    SHT_STRTAB
+    Address: 0x1000
+    Size:    0x10
+    Content: "004400550066007700"
+  - Name: .dynamic
+    Type: SHT_DYNAMIC
+    Entries:
+     - Tag:   DT_NEEDED
+       Value: 0x1245657656
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jh7370 wrote:

You shouldn't be reading memory outside the file image, or you could end up trying to read memory belonging e.g. to another a process entirely (depending on how memory safety works on your particular OS). A crash is just one of possible behaviours. For example, it's not impossible you'd print something that appears meaningful but is actually completely bogus.

As a valid virtual address will depend on the host OS, that isn't something that is worth targeting. Instead, the thing you should be targeting is where the behaviour changes - namely when the address points at or past the end of the string table. In that way, you can show you get the warning when the value reaches the bad point, but not when it is just before. We don't need to trigger a crash, showing that we don't read bogus data is good enough, since it's the same problem.

https://github.com/llvm/llvm-project/pull/125679