https://llvm.org/bugs/show_bug.cgi?id=26129
Bug ID: 26129
Summary: [Mips] backend emits JAL instructions truncating the
jump address
Product: new-bugs
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: normal
Priority: P
Component: new bugs
Assignee: unassignedb...@nondot.org
Reporter: d...@codeplay.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
Hi,
when invoking a function through an absolute address, the mips backend emits
the JAL instruction. This is fine only when the address happens to be in the
same "PC-region branch", as the most significant part of the address is based
on the PC. Otherwise truncation happens and the behaviour is incorrect.
Repro, consider this snippet:
define i32 @foo(i32 signext %a, i32 signext %b) #0 {
%1 = tail call i32 inttoptr (i32 1073741824 to i32 (i32, i32)*)(i32 signext
%a, i32 signext %b) #1
ret i32 0
}
obtained by clang --target=mipsel--linux-android -O2 -c -emit-llvm -o sample.bc
sample.c
int foo(int a, int b){
int (*f) (int, int) = (int (*) (int, int)) 0x40000000; // 1 Gb
f(a, b); // Jumps to 0!
return 0;
}
Compile with llc -filetype=obj -mtriple=mipsel--linux-android sample.bc -o
sample.o:
Disassembly of section .text:
foo:
0: e8 ff bd 27 addiu $sp, $sp, -24
4: 14 00 bf af sw $ra, 20($sp)
8: 00 00 00 0c jal 0 // boom
c: 00 00 00 00 nop
10: 00 00 02 24 addiu $2, $zero, 0
14: 14 00 bf 8f lw $ra, 20($sp)
18: 08 00 e0 03 jr $ra
1c: 18 00 bd 27 addiu $sp, $sp, 24
This is a bug being around for some time affecting the JIT capability of LLDB
for Mips.
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