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marfrit 00d655187a benchmark/: three-way RE-tool comparison + first real C-lift

Three small functions extracted from the v1.19 conservative blob with
ground-truth C and per-tool (Ghidra / retdec / decomp.me) docs:
  01_memset        — byte memset, 28 B
  02_memcpy32      — word-aligned memcpy, 36 B
  03_magic_memset  — magic check + tail-call to memset, 40 B
  04_train_phy_block — first real poll-site function (104 B, 26 insts),
                       contains poll sites 12-15

Results in RESULTS.md:
  - Ghidra: A on all four. Auto-decompile is close to final.
  - retdec: A on #3, F on #1 and #2 (no register-arg inference on raw),
    C on #4 (mistakes & 0xF0000000 for < 0x10000000).

GRIND_LOG.md (in 04_train_phy_block/) records the matching-decomp
iteration: 116-byte candidate.c at -Os vs vendor 104 bytes = 89.7%
size match on first real iteration. Remaining gap is GCC's choice of
`cmp w, w_const; b.ls` over vendor's `tst w, #imm; b.eq` for the
mask tests.

gdb_debug/ holds a native-aarch64 GDB single-stepper for the three
benchmark functions — boltzmann smoke test passed (memset:
buf[10] 0x00→0xab).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

2026-04-15 07:26:23 +02:00

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decomp.me recipe — 01_memset

Create a scratch

Open https://decomp.me/ (or your self-hosted instance at http://192.168.88.64 if available). Click New scratch.

Platform / Compiler: gcc 12.x aarch64-linux-gnu (or whatever aarch64-gcc is offered — exact version doesn't matter much for this size).
Compiler flags: -O2 -ffreestanding -nostdlib
Diff label: memset_byte

Target asm

Paste the following into the "Target asm" box:

memset_byte:
    mov     x3, #0x0
.Lloop:
    cmp     x2, x3
    b.ne    .Lbody
    ret
.Lbody:
    strb    w1, [x0, x3]
    add     x3, x3, #0x1
    b       .Lloop

Context (headers/decls)

#include <stddef.h>
#include <stdint.h>

Source

Paste the ground-truth C from reference.c (or write your own first and iterate).

Expected workflow

First compile: scorer usually reports a high similarity (>= 80%) if the compiler picks the same while (i != n) pattern.
Fine-tune: try i++ vs i+=1, try while vs for, try uint8_t * cast placement. Each yields a distinct register-allocation order the scorer rewards or punishes.
Perfect match possible if you hit the exact code shape GCC chose.

Benchmark notes

decomp.me's strength is the compile-and-diff feedback loop — every edit immediately shows the byte-delta against the target.
Weakness for this target: the real blob was likely built with a different compiler (ARMCC / Keil / vendor LLVM?). GCC may never match exactly even with perfect C. Similarity >= 90% is the realistic ceiling.

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