[lld] ELF: Introduce --randomize-section-padding option. (PR #117653)

[via llvm-commits]

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+# REQUIRES: x86
+# RUN: split-file %s %t
+# RUN: llvm-mc -filetype=obj -triple=x86_64 %t/a.s -o %t/a.o
+
+## --randomize-section-padding= inserts segment offset padding and pre-section
+## padding, and does not affect flags. Segment offset padding is only inserted
+## when PT_LOAD changes, as shown by .bss size (.data and .bss share a PT_LOAD).
+
+# RUN: ld.lld --randomize-section-padding=6 %t/a.o -o %t/a.out
+# RUN: llvm-readelf -sS -x .rodata -x .text -x .data %t/a.out | FileCheck --check-prefix=PAD6 %s
+
+# PAD6: .rodata           PROGBITS        0000000000200158 000158 000b8d 00   A  0   0  1
+# PAD6: .text             PROGBITS        0000000000201ce8 000ce8 000270 00  AX  0   0  4
+# PAD6: .data             PROGBITS        0000000000202f58 000f58 000941 00  WA  0   0  1
+# PAD6: .bss              NOBITS          0000000000203899 001899 000003 00  WA  0   0  1
+
+# PAD6: 0000000000203899     0 NOTYPE  LOCAL  DEFAULT     4 a
+# PAD6: 000000000020389a     0 NOTYPE  LOCAL  DEFAULT     4 b
+# PAD6: 000000000020389b     0 NOTYPE  LOCAL  DEFAULT     4 c
+
+# PAD6: Hex dump of section '.rodata':
+# PAD6: 0x00200cd8 00000000 00000000 00000102 03
+# PAD6: Hex dump of section '.text':
+# PAD6: 0x00201f48 cccccccc cccccccc cccccccc 0405cc06
+# PAD6: Hex dump of section '.data':
+# PAD6: 0x00203888 00000000 00000000 00000000 00000708
+# PAD6: 0x00203898 09
+
+## Size of segment offset padding and location of pre-section padding is
+## dependent on the seed.
+
+# RUN: ld.lld --randomize-section-padding=46 %t/a.o -o %t/a.out
+# RUN: llvm-readelf -sS -x .rodata -x .text -x .data %t/a.out | FileCheck --check-prefix=PAD46 %s
+
+# PAD46: .rodata           PROGBITS        0000000000200158 000158 000cc0 00   A  0   0  1
+# PAD46: .text             PROGBITS        0000000000201e18 000e18 0009bf 00  AX  0   0  4
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pcc wrote:

Done

https://github.com/llvm/llvm-project/pull/117653