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<p>Hi, Sergey,</p>
<p>thanks for the patch!</p>
<p>See my comments below.</p>
<p>Sergey<br>
</p>
<div class="moz-cite-prefix">On 26.08.2024 13:25, Sergey Kaplun
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:20240826102520.29541-1-skaplun@tarantool.org">
<pre class="moz-quote-pre" wrap="">From: Mike Pall <mike>
Reported by pwnhacker0x18.
(cherry picked from commit 4fc48c50fe3f3f5a9680bada5c0c0d0d7eb345a3)
When compiling `string.format()` with a huge sequence of elements, it is
possible that too many KGC IRs underflow the IR buffer. This patch
limits the maximum number of `string.format()` elements to be compiled
to 100.
Sergey Kaplun:
* added the description and the test for the problem
Part of tarantool/tarantool#10199
---
Branch: <a class="moz-txt-link-freetext" href="https://github.com/tarantool/luajit/tree/skaplun/lj-1203-limit-format-elements">https://github.com/tarantool/luajit/tree/skaplun/lj-1203-limit-format-elements</a>
Related issues:
* <a class="moz-txt-link-freetext" href="https://github.com/tarantool/tarantool/issues/10199">https://github.com/tarantool/tarantool/issues/10199</a>
* <a class="moz-txt-link-freetext" href="https://github.com/LuaJIT/LuaJIT/issues/1203">https://github.com/LuaJIT/LuaJIT/issues/1203</a>
src/lj_ffrecord.c | 2 ++
.../lj-1203-limit-format-elements.test.lua | 28 +++++++++++++++++++
2 files changed, 30 insertions(+)
create mode 100644 test/tarantool-tests/lj-1203-limit-format-elements.test.lua
diff --git a/src/lj_ffrecord.c b/src/lj_ffrecord.c
index d5fc081e..3b82d044 100644
--- a/src/lj_ffrecord.c
+++ b/src/lj_ffrecord.c
@@ -962,6 +962,7 @@ static void LJ_FASTCALL recff_string_format(jit_State *J, RecordFFData *rd)
TRef hdr, tr;
FormatState fs;
SFormat sf;
+ int nfmt = 0;
/* Specialize to the format string. */
emitir(IRTG(IR_EQ, IRT_STR), trfmt, lj_ir_kstr(J, fmt));
tr = hdr = recff_bufhdr(J);
@@ -1031,6 +1032,7 @@ static void LJ_FASTCALL recff_string_format(jit_State *J, RecordFFData *rd)
recff_nyiu(J, rd);
return;
}
+ if (++nfmt > 100) lj_trace_err(J, LJ_TRERR_TRACEOV);
}
J->base[0] = emitir(IRT(IR_BUFSTR, IRT_STR), tr, hdr);
}
diff --git a/test/tarantool-tests/lj-1203-limit-format-elements.test.lua b/test/tarantool-tests/lj-1203-limit-format-elements.test.lua
new file mode 100644
index 00000000..f17d4e37
--- /dev/null
+++ b/test/tarantool-tests/lj-1203-limit-format-elements.test.lua
@@ -0,0 +1,28 @@
+local tap = require('tap')
+
+-- Test file to demonstrate LuaJIT incorrect recording of
+-- `string.format()` function with huge amount of elements.
+-- See also: <a class="moz-txt-link-freetext" href="https://github.com/LuaJIT/LuaJIT/issues/1173">https://github.com/LuaJIT/LuaJIT/issues/1173</a>.</pre>
</blockquote>
Seems a correct link is <a class="moz-txt-link-freetext" href="https://github.com/LuaJIT/LuaJIT/issues/1203">https://github.com/LuaJIT/LuaJIT/issues/1203</a><br>
<blockquote type="cite"
cite="mid:20240826102520.29541-1-skaplun@tarantool.org">
<pre class="moz-quote-pre" wrap="">
+
+local test = tap.test('lj-1203-limit-format-elements'):skipcond({
+ ['Test requires JIT enabled'] = not jit.status(),
+})
+
+test:plan(2)
+
+jit.opt.start('hotloop=1')
+
+-- XXX: Use a huge amount of format elements to process, which
+-- creates a lot of string constants.
+local NELEMENTS = 25000</pre>
</blockquote>
<p>Why 25000? It is reproduced with 10000 as well.<br>
</p>
<p><br>
</p>
<blockquote type="cite"
cite="mid:20240826102520.29541-1-skaplun@tarantool.org">
<pre class="moz-quote-pre" wrap="">
+local fmt = ('%'):rep(NELEMENTS * 2)
+local expected = ('%'):rep(NELEMENTS)
+local result
+for _ = 1, 4 do
+ result = fmt:format()
+end
+
+test:ok(true, 'no IR buffer underflow')</pre>
</blockquote>
Why do you need this check? Why the following check it not enough?<br>
<blockquote type="cite"
cite="mid:20240826102520.29541-1-skaplun@tarantool.org">
<pre class="moz-quote-pre" wrap="">
+test:is(result, expected, 'correct result')
+
+test:done(true)
</pre>
</blockquote>
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