[llvm] [DWARFVerifier] Verify that DW_AT_LLVM_stmt_sequence is set correctly (PR #152807)

[David Blaikie via llvm-commits]

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+# Object file copied from llvm/test/tools/dsymutil/ARM/stmt-seq-macho.test
+# Then manually tempered with some of the value of the attribute
+# I hope there are easier ways to construct tests like this.
+
+# RUN: yaml2obj %s -o verify_stmt_seq.o
+# RUN: not llvm-dwarfdump -verify -debug-info verify_stmt_seq.o | FileCheck %s --check-prefix=CHECK_INVALID --implicit-check-not=error:
+# RUN: llvm-dwarfdump -debug-line -verbose -debug-info verify_stmt_seq.o | FileCheck %s --check-prefix=CHECK_DEBUG_LINE
+
+
+# CHECK_INVALID: error: DW_AT_LLVM_stmt_sequence offset 0x00000000 is not within the line table bounds [0x0000002e, 0x000000fd)
+# CHECK_INVALID: DW_AT_LLVM_stmt_sequence [DW_FORM_sec_offset]     (0x00000000)
+
+# 0xd3 would be a valid offset, if the line table wan't ill formed with two rows having the same PC (0x8c).
+# CHECK_INVALID: error: DW_AT_LLVM_stmt_sequence offset 0x000000d3 does not point to a valid sequence offset in the line table
+# CHECK_INVALID: DW_AT_LLVM_stmt_sequence [DW_FORM_sec_offset]     (0x000000d3)
+
+# CHECK_DEBUG_LINE:      0x000000d3: 05 DW_LNS_set_column (85)
+# CHECK_DEBUG_LINE-NEXT: 0x000000d5: 0a DW_LNS_set_prologue_end
+# CHECK_DEBUG_LINE-NEXT: 0x000000d6: 00 DW_LNE_set_address (0x000000000000008c)
+# CHECK_DEBUG_LINE-NEXT: 0x000000e1: 03 DW_LNS_advance_line (30)
+# CHECK_DEBUG_LINE-NEXT: 0x000000e3: 01 DW_LNS_copy
+# CHECK_DEBUG_LINE-NEXT:             0x000000000000008c     30     85      1   0             0       0  is_stmt prologue_end
+# CHECK_DEBUG_LINE-NEXT: 0x000000e4: 00 DW_LNE_end_sequence
+# CHECK_DEBUG_LINE-NEXT:             0x000000000000008c     30     85      1   0             0       0  is_stmt end_sequence
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dwblaikie wrote:

I'd say there's some extra nuance here:

* Agreed it's incorrect to describe a function of length 1 with a sequence of length 0
* But it /may/ be sort of valid to describe a function as having length 0 (in which case two functions could have the same address) - this can happen in UB situations for C++ (well, not technically UB if th efunction is never called), like this: https://godbolt.org/z/efhK69TMG (f1 has an address range [0, 0), f2 has an address range [0, 1)) - we /probably/ want to get rid of these as they break DWARF in other ways, and are more of a hazard than they need to be (it's not especially expensive to have such functions include a trap instruction rather than be truly zero-length) but it is a thing that exists today

https://github.com/llvm/llvm-project/pull/152807