DISASSEMBLE can display wrong code section (sbcl-2.4.0)

[Fedorov Alexander]

* (labels ((f (val) (when val (g nil)))
           (g (val) (when val (f nil))))
    (defun foo (x)
      (if x #'f #'g)))
FOO
* (disassemble (foo t))
; disassembly for (LABELS F)
; Size: 41 bytes. Origin: #x549CD1C0
; C0: .ENTRY (LABELS F)(VAL)
; D0: 8F4508 POP QWORD PTR [RBP+8]
; D3: 83F902 CMP ECX, 2
; D6: 750F JNE L0
; D8: 488D65E0 LEA RSP, [RBP-32]
; DC: 488BF2 MOV RSI, RDX
; DF: EBBA JMP #x549CD19B
; E1: CC10 INT3 16 ; Invalid argument count trap
; E3: CC10 INT3 16 ; Invalid argument count trap
; E5: CC10 INT3 16 ; Invalid argument count trap
; E7: L0: CC10 INT3 16 ; Invalid argument count trap
NIL

The shown code segment is a stripped version of (XEP (LABELS F)), as can be seen from

* (sb-disassem:disassemble-code-component #'foo)
; Size: 297 bytes. Origin: #x549CD0C0 (segment 1 of 8) ; (XEP (LAMBDA ()))
; 0C0: .ENTRY (LAMBDA NIL)
; 0D0: 8F4508 POP QWORD PTR [RBP+8]
; 0D3: 85C9 TEST ECX, ECX
; 0D5: 0F8506010000 JNE L9
; 0DB: 488D65E0 LEA RSP, [RBP-32]
; Origin #x549CD0DF (segment 2 of 8) ; (LAMBDA ())
; 0DF: 498B4510 MOV RAX, [R13+16] ; thread.binding-stack-pointer
; 0E3: 488945F8 MOV [RBP-8], RAX
; 0E7: 488D3D2D000000 LEA RDI, [RIP+45] ; = L0
; 0EE: 488B15B3FFFFFF MOV RDX, [RIP-77] ; 'FOO
; 0F5: B904000000 MOV ECX, 4
; 0FA: FF7508 PUSH QWORD PTR [RBP+8]
; 0FD: B8C2E12550 MOV EAX, #x5025E1C2 ; #<FDEFN SB-IMPL::%DEFUN>
; 102: FFE0 JMP RAX
; Origin #x549CD104 (segment 3 of 8) ; (XEP FOO)
; 104: .SKIP 12
; 110: L0: .ENTRY FOO(X)
; 120: 8F4508 POP QWORD PTR [RBP+8]
; 123: 83F902 CMP ECX, 2
; 126: 0F85B7000000 JNE L10
; 12C: 488D65E0 LEA RSP, [RBP-32]
; 130: 488BF2 MOV RSI, RDX
; Origin #x549CD133 (segment 4 of 8) ; FOO
; 133: 498B4510 MOV RAX, [R13+16] ; thread.binding-stack-pointer
; 137: 488945F0 MOV [RBP-16], RAX
; 13B: 4881FE17010050 CMP RSI, #x50000117 ; NIL
; 142: 750A JNE L2
; 144: 488D1520000000 LEA RDX, [RIP+32] ; = L3
; 14B: L1: C9 LEAVE
; 14C: F8 CLC
; 14D: C3 RET
; 14E: L2: 488D1576000000 LEA RDX, [RIP+118] ; = L8
; 155: EBF4 JMP L1
; Origin #x549CD157 (segment 5 of 8) ; (XEP (LABELS G))
; 157: .SKIP 9
; 160: L3: .ENTRY (LABELS G)(VAL)
; 170: 8F4508 POP QWORD PTR [RBP+8]
; 173: 83F902 CMP ECX, 2
; 176: 756D JNE L11
; 178: 488D65E0 LEA RSP, [RBP-32]
; 17C: 4C8BC2 MOV R8, RDX
; Origin #x549CD17F (segment 6 of 8) ; (LABELS G)
; 17F: L4: 498B4510 MOV RAX, [R13+16] ; thread.binding-stack-pointer
; 183: 488945E8 MOV [RBP-24], RAX
; 187: 4981F817010050 CMP R8, #x50000117 ; NIL
; 18E: 7506 JNE L5
; 190: 498BD0 MOV RDX, R8
; 193: C9 LEAVE
; 194: F8 CLC
; 195: C3 RET
; 196: L5: BE17010050 MOV ESI, #x50000117 ; NIL
; Origin #x549CD19B (segment 7 of 8) ; (LABELS F)
; 19B: L6: 498B4510 MOV RAX, [R13+16] ; thread.binding-stack-pointer
; 19F: 488945E0 MOV [RBP-32], RAX
; 1A3: 4881FE17010050 CMP RSI, #x50000117 ; NIL
; 1AA: 7506 JNE L7
; 1AC: 488BD6 MOV RDX, RSI
; 1AF: C9 LEAVE
; 1B0: F8 CLC
; 1B1: C3 RET
; 1B2: L7: 41B817010050 MOV R8D, #x50000117 ; NIL
; 1B8: EBC5 JMP L4
; Origin #x549CD1BA (segment 8 of 8) ; (XEP (LABELS F))
; 1BA: .SKIP 6
; 1C0: L8: .ENTRY (LABELS F)(VAL) <------------------------------------------------- HERE
; 1D0: 8F4508 POP QWORD PTR [RBP+8]
; 1D3: 83F902 CMP ECX, 2
; 1D6: 750F JNE L12
; 1D8: 488D65E0 LEA RSP, [RBP-32]
; 1DC: 488BF2 MOV RSI, RDX
; 1DF: EBBA JMP L6
; 1E1: L9: CC10 INT3 16 ; Invalid argument count trap
; 1E3: L10: CC10 INT3 16 ; Invalid argument count trap
; 1E5: L11: CC10 INT3 16 ; Invalid argument count trap
; 1E7: L12: CC10 INT3 16 ; Invalid argument count trap
NIL

This is a regression, this behavior started in sbcl-2.2.1 (starting with this commit: https://github.com/sbcl/sbcl/commit/be5c6d037ba032717638f21d515444cf255e4cbd)

Tested on sbcl-2.4.0 (and on HEAD: sbcl-2.4.0.239-28ab0f952)

uname -a
Linux grolter-T16 6.2.0-39-generic #40-Ubuntu SMP PREEMPT_DYNAMIC Tue Nov 14 14:18:00 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux

* *features*
(:ARENA-ALLOCATOR :X86-64 :GENCGC :64-BIT :ANSI-CL :COMMON-LISP :ELF
 :IEEE-FLOATING-POINT :LINUX :LITTLE-ENDIAN :PACKAGE-LOCAL-NICKNAMES
 :SB-CORE-COMPRESSION :SB-LDB :SB-PACKAGE-LOCKS :SB-THREAD :SB-UNICODE :SBCL
 :UNIX)

[Stas Boukarev (stassats)]

It's because they are unusually laid out in memory, xep follows the function, so probably it's better to just change the layout.

And it's not really a regression from be5c6d037ba032717638f21d515444cf255e4cbd, because before that (disassemble (foo t)) shows just one function, but (disassemble (foo nil)) shows two functions, so it was just as non-consistent before.