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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - When compiling for arch armv6kz, __ARM_FEATURE_LDREX predefined incorrectly"
href="https://bugs.llvm.org/show_bug.cgi?id=38553">38553</a>
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<th>Summary</th>
<td>When compiling for arch armv6kz, __ARM_FEATURE_LDREX predefined incorrectly
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Driver
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>sethml@ofb.net
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>When compiling with arch armv6kz, __ARM_FEATURE_LDREX is predefined to 0x4,
while when compiling for armv6k it's predefined to 0xf:
% clang++ -E -dM --target=arm-linux-gnueabihf -march=armv6kz - </dev/null |
grep LDREX
#define __ARM_FEATURE_LDREX 0x4
% clang++ -E -dM --target=arm-linux-gnueabihf -march=armv6k - </dev/null | grep
LDREX
#define __ARM_FEATURE_LDREX 0xf
According to ARM's document "ARM® C Language Extensions Release 2.0":
<a href="http://infocenter.arm.com/help/topic/com.arm.doc.ihi0053c/IHI0053C_acle_2_0.pdf">http://infocenter.arm.com/help/topic/com.arm.doc.ihi0053c/IHI0053C_acle_2_0.pdf</a>
The following values of __ARM_FEATURE_LDREX may occur:
Macro value | Access widths | Example architecture
(undefined) | none | ARM v5, ARM v6-M
0x04 | word | ARM v6
0x07 | word, halfword, byte | ARM v7-M
0x0F | doubleword, word, halfword, byte | ARM v6K, ARM v7-A/R
The "armv6kz" architecture is a synonym for "armv6z" and "armv6zk". It's the
architecture implemented by the ARM1176JZF-S CPU which is used in all older
Raspberry Pis, so it's a surprisingly common architecture. It's a bit hard to
find an authoritative reference in ARM's documentation, but armv6kz is a
superset of armv6k. The "ARM® Architecture Reference Manual ARMv7-A and ARMv7-R
edition" on page 1156 says:
<a href="https://static.docs.arm.com/ddi0406/c/DDI0406C_C_arm_architecture_reference_manual.pdf">https://static.docs.arm.com/ddi0406/c/DDI0406C_C_arm_architecture_reference_manual.pdf</a>
Note:
The Security Extensions are also permitted as an extension to the ARMv6K
architecture. The resulting combination is sometimes called the ARMv6Z or
ARMv6KZ
architecture.
As such, on this architecture __ARM_FEATURE_LDREX should be defined to 0xf.
I'm not in a position to test and submit a patch, but I think the fix is
simple. In lib/Basic/Targets/ARM.cpp ARMTargetInfo::handleTargetFeatures(),
change:
else if (ArchKind == llvm::ARM::ArchKind::ARMV6K)
LDREX = LDREX_D | LDREX_W | LDREX_H | LDREX_B;
to:
else if (ArchKind == llvm::ARM::ArchKind::ARMV6K ||
ArchKind == llvm::ARM::ArchKind::ARMV6KZ)
LDREX = LDREX_D | LDREX_W | LDREX_H | LDREX_B;</pre>
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