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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [ms] clang-cl emits code that causes link.exe /incremental to write broken binaries, related to function pointers"
href="https://llvm.org/bugs/show_bug.cgi?id=25891">25891</a>
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</tr>
<tr>
<th>Summary</th>
<td>[ms] clang-cl emits code that causes link.exe /incremental to write broken binaries, related to function pointers
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Windows NT
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>LLVM Codegen
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>nicolasweber@gmx.de
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>First, create these 3 files:
C:\src\chrome\src\net>type s3.h
typedef struct ssl_st SSL;
struct ssl_st {
void* f[21]; // <- !
int (*handshake_func)(SSL *);
void (*info_callback)();
};
C:\src\chrome\src\net>type s3_clnt.c
#include "s3.h"
#include <stddef.h>
void f();
#define FOO0 f(); f();
#define FOO1 FOO0 FOO0
#define FOO2 FOO1 FOO1
#define FOO3 FOO2 FOO2
#define FOO4 FOO3 FOO3
#define FOO5 FOO4 FOO4
#define FOO6 FOO5 FOO5
#define FOO7 FOO6 FOO6
#define FOO8 FOO7 FOO7
#define FOO9 FOO8 FOO8
#define FOO10 FOO9 FOO9
#define FOO11 FOO10 FOO10
int ssl3_connect(SSL *s) {
if (s->info_callback != NULL)
s->info_callback();
// Bloat code size a bit so it's more likely link.exe writes a new version
// of this function.
FOO11
return 0;
}
C:\src\chrome\src\net>type s3_lib.c
#include <stdlib.h>
#include <string.h>
#include "s3.h"
int ssl3_connect(SSL *s);
void f() {}
int main() {
SSL *s = (SSL *)malloc(sizeof(SSL));
memset(s, 0, sizeof(SSL));
s->handshake_func = ssl3_connect;
s->handshake_func(s);
}
Then build them like so:
C:\src\chrome\src\net>"..\third_party\llvm-build\Release+Asserts\bin\clang-cl.exe"
/c s3_clnt.c /O2
C:\src\chrome\src\net>"..\third_party\llvm-build\Release+Asserts\bin\clang-cl.exe"
/c s3_lib.c /O2
C:\src\chrome\src\net>link /incremental s3_clnt.obj s3_lib.obj
/out:net_repro.exe
Microsoft (R) Incremental Linker Version 12.00.31101.0
Copyright (C) Microsoft Corporation. All rights reserved.
Now run net_repro.exe. It should exit fine.
Now increment the number in the line marked "// <- !" by one, rerun the three
build commands, and run the executable again. You my need to do this 2-5 times,
but sometimes once is enough. Eventually, the executable will crash with a
stack overflow. It looks like `s->handshake_func(s)` jumps to an old version of
ssl3_connect() where the offset is 8 bytes too low, so that `s->info_callback`
isn't NULL but points ot `s->handshake_func` again.</pre>
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