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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [ARM] Thumb `__builtin_longjmp` back to ARM broken for Linux"
href="https://bugs.llvm.org/show_bug.cgi?id=51681">51681</a>
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<th>Summary</th>
<td>[ARM] Thumb `__builtin_longjmp` back to ARM broken for Linux
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Backend: ARM
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>xtkoba@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, smithp352@googlemail.com, Ties.Stuij@arm.com
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<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=25205" name="attach_25205" title="Repro">attachment 25205</a> <a href="attachment.cgi?id=25205&action=edit" title="Repro">[details]</a></span>
Repro
$ cat thumb-blj.c
void blj(void *jmp_buf[5])
{
__asm__ __volatile__ ("movs r2, #0\n\t"
"mov r11, r2" : : : "r2", "r11");
__builtin_longjmp(jmp_buf, 1);
return;
}
$ cat arm-bsj.c
void *jmp_buf[5];
void blj(void *[5]);
int foo(void)
{
volatile int i = 0;
if (__builtin_setjmp(jmp_buf) == 0) {
i++;
blj(jmp_buf);
} else {
i++;
}
return i;
}
int main(void)
{
return foo() - 2;
}
$ clang -mthumb thumb-blj.c -c
$ clang -marm arm-bsj.c thumb-blj.o
Then
$ ./a.out
will segfault.
This is because R11 is not restored from the jump buffer. Let's look at the
disassembly of thumb-blj.o:
$ llvm-objdump thumb-blj.o -d
thumb-blj.o: file format elf32-littlearm
Disassembly of section .text:
00000000 <blj>:
0: 80 b5 push {r7, lr}
2: 6f 46 mov r7, sp
4: 4d f8 04 bd str r11, [sp, #-4]!
8: 81 b0 sub sp, #4
a: 00 90 str r0, [sp]
c: 00 22 movs r2, #0
e: 93 46 mov r11, r2
10: 00 98 ldr r0, [sp]
12: 00 21 movs r1, #0
14: 81 68 ldr r1, [r0, #8]
16: 8d 46 mov sp, r1
18: 41 68 ldr r1, [r0, #4]
1a: 07 68 ldr r7, [r0]
1c: 03 68 ldr r3, [r0]
1e: 08 47 bx r1
I suppose the instruction at 0x1c is intended to be something like
ldr r11, [r0]
but this is illegal for Thumb because R11 is a high register.</pre>
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