With arm32, the ABI gives us 8-byte alignment for the stack.
While it's possible to realign the stack to provide 16-byte alignment,
it's far easier to simply not encode 16-byte alignment in the
VLD1 and VST1 instructions that we emit.
Remove the assertion in temp_allocate_frame, limit natural alignment
to the provided stack alignment, and add a comment.
Reported-by: Richard W.M. Jones <rjo...@redhat.com>
Signed-off-by: Richard Henderson <richard.hender...@linaro.org>
---
I haven't seen the assertion with the various arm kernels that I happen
to have laying about. I have not taken the time to build the combo
from the bug report:
[ 0.000000] Linux version 5.14.0-60.fc36.armv7hl
(mockbu...@buildvm-a32-12.iad2.fedoraproject.org) (gcc (GCC) 11.2.1 20210728
(Red Hat 11.2.1-1), GNU ld version 2.37-9.fc36) #1 SMP Mon Aug 30 14:08:34 UTC
2021
I thought about parameterizing this patch further, but I can't think of
another ISA that would be affected. (i686 clumsily changed its abi 20
years ago to avoid faulting on vector spills; other isas so far have
allowed vectors to be unaligned.)
r~
---
tcg/tcg.c | 8 +++++++-
tcg/arm/tcg-target.c.inc | 13 +++++++++----
2 files changed, 16 insertions(+), 5 deletions(-)
diff --git a/tcg/tcg.c b/tcg/tcg.c
index 4142d42d77..ca5bcc4635 100644
--- a/tcg/tcg.c
+++ b/tcg/tcg.c
@@ -3060,7 +3060,13 @@ static void temp_allocate_frame(TCGContext *s, TCGTemp
*ts)
g_assert_not_reached();
}
- assert(align <= TCG_TARGET_STACK_ALIGN);
+ /*
+ * Assume the stack is sufficiently aligned.
+ * This affects e.g. ARM NEON, where we have 8 byte stack alignment
+ * and do not require 16 byte vector alignment. This seems slightly
+ * easier than fully parameterizing the above switch statement.
+ */
+ align = MIN(TCG_TARGET_STACK_ALIGN, align);
off = ROUND_UP(s->current_frame_offset, align);
/* If we've exhausted the stack frame, restart with a smaller TB. */
diff --git a/tcg/arm/tcg-target.c.inc b/tcg/arm/tcg-target.c.inc
index e5b4f86841..8515717435 100644
--- a/tcg/arm/tcg-target.c.inc
+++ b/tcg/arm/tcg-target.c.inc
@@ -2477,8 +2477,13 @@ static void tcg_out_ld(TCGContext *s, TCGType type,
TCGReg arg,
tcg_out_vldst(s, INSN_VLD1 | 0x7d0, arg, arg1, arg2);
return;
case TCG_TYPE_V128:
- /* regs 2; size 8; align 16 */
- tcg_out_vldst(s, INSN_VLD1 | 0xae0, arg, arg1, arg2);
+ /*
+ * We have only 8-byte alignment for the stack per the ABI.
+ * Rather than dynamically re-align the stack, it's easier
+ * to simply not request alignment beyond that. So:
+ * regs 2; size 8; align 8
+ */
+ tcg_out_vldst(s, INSN_VLD1 | 0xad0, arg, arg1, arg2);
return;
default:
g_assert_not_reached();
@@ -2497,8 +2502,8 @@ static void tcg_out_st(TCGContext *s, TCGType type,
TCGReg arg,
tcg_out_vldst(s, INSN_VST1 | 0x7d0, arg, arg1, arg2);
return;
case TCG_TYPE_V128:
- /* regs 2; size 8; align 16 */
- tcg_out_vldst(s, INSN_VST1 | 0xae0, arg, arg1, arg2);
+ /* See tcg_out_ld re alignment: regs 2; size 8; align 8 */
+ tcg_out_vldst(s, INSN_VST1 | 0xad0, arg, arg1, arg2);
return;
default:
g_assert_not_reached();
--
2.25.1
