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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 - Incorrect debug values for parameters that are smaller than stack slots"
href="https://bugs.llvm.org/show_bug.cgi?id=40973">40973</a>
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<th>Summary</th>
<td>Incorrect debug values for parameters that are smaller than stack slots
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>DebugInfo
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>david.stenberg@ericsson.com
</td>
</tr>
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<th>CC</th>
<td>jdevlieghere@apple.com, keith.walker@arm.com, llvm-bugs@lists.llvm.org, paul_robinson@playstation.sony.com
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<pre>Spawned out from D58831.
When compiling the following test case:
extern void bar(short);
void foo(int p0, int p1, int p2, int p3, short p4, short p5) {
bar(p4);
}
using clang from trunk (r355379):
$ clang --target=arm -mbig-endian -O2 -g
we land up with the following debug information for p4 and p5:
0x0000006d: DW_TAG_formal_parameter
DW_AT_name ("p4")
DW_AT_decl_file
("/home/user/upstream/master/stack_dbg_values.c")
DW_AT_decl_line (3)
DW_AT_type (0x0000008e "short")
0x00000078: DW_TAG_formal_parameter
DW_AT_location (DW_OP_breg13 SP+4)
DW_AT_name ("p5")
DW_AT_decl_file
("/home/user/upstream/master/stack_dbg_values.c")
DW_AT_decl_line (3)
DW_AT_type (0x0000008e "short")
I think there are two issues here. For p4, we do not consider truncates when
searching for the FI in SelectionDAGBuilder::EmitFuncArgumentDbgValue(),
meaning that we are left with a $noreg DBG_VALUE, ultimately leading to no
location being emitted for the parameter. For p5, we say that it is located on
the stack at offset 4, but as we are on a big-endian target the two-byte short
parameter is located in the lower two bytes of the 4-byte stack slot, meaning
that the offset should really be 6.
Compare this with the output from GCC (5.4.1):
$ arm-none-eabi-gcc -O1 -g -mbig-endian stack_dbg_values.c -c
0x00000072: DW_TAG_formal_parameter
DW_AT_name ("p4")
DW_AT_decl_file
("/home/user/upstream/master/stack_dbg_values.c")
DW_AT_decl_line (3)
DW_AT_type (0x000000a6 "short int")
DW_AT_location (DW_OP_fbreg +2)
0x0000007f: DW_TAG_formal_parameter
DW_AT_name ("p5")
DW_AT_decl_file
("/home/user/upstream/master/stack_dbg_values.c")
DW_AT_decl_line (3)
DW_AT_type (0x000000a6 "short int")
DW_AT_location (DW_OP_fbreg +6)</pre>
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