Alex Richardson has uploaded this change for review. (
https://gem5-review.googlesource.com/c/public/gem5/+/56103 )
Change subject: arch-riscv: Fix (c.)addiw sign-extension behaviour
......................................................................
arch-riscv: Fix (c.)addiw sign-extension behaviour
Previously calling a function with an INT_MAX argument would result in
the following (incorrectly extended) trace:
```
lui a1, 524288 : IntAlu : D=0xffffffff80000000
c_addiw a1, -1 : IntAlu : D=0xffffffff7fffffff
```
I noticed this due to a kernel assertion that checked the second argument
was bigger than the first. Since INT_MAX was incorrectly being extended to
0xffffffff7fffffff, the generated slt comparison instruction was returning
1 instead of the expected zero (which would have happened with 0x7fffffff).
The problem in the current addiw logic is that the immediate value is an
int64_t, so the 32-bit Rs1/Rc1 values are promoted to 64-bit for the
aritmetic operation, thereby making the current cast redundant.
Fix this by placing parens around the whole expression and truncating
that to 32 bits.
Change-Id: I7b18a8101b1c2614b9f056004e6a7f87b66b64c9
---
M src/arch/riscv/isa/decoder.isa
1 file changed, 28 insertions(+), 2 deletions(-)
diff --git a/src/arch/riscv/isa/decoder.isa b/src/arch/riscv/isa/decoder.isa
index 3cbba5a..e512e08 100644
--- a/src/arch/riscv/isa/decoder.isa
+++ b/src/arch/riscv/isa/decoder.isa
@@ -135,7 +135,7 @@
return std::make_shared<IllegalInstFault>(
"source reg x0", machInst);
}
- Rc1_sd = (int32_t)Rc1_sd + imm;
+ Rc1_sw = (int32_t)(Rc1_sw + imm);
}});
0x2: c_li({{
imm = CIMM5;
@@ -471,7 +471,7 @@
0x06: decode FUNCT3 {
format IOp {
0x0: addiw({{
- Rd_sd = Rs1_sw + imm;
+ Rd_sw = (int32_t)(Rs1_sw + imm);
}}, int32_t);
0x1: slliw({{
Rd_sd = Rs1_sw << imm;
--
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Gerrit-Project: public/gem5
Gerrit-Branch: develop
Gerrit-Change-Id: I7b18a8101b1c2614b9f056004e6a7f87b66b64c9
Gerrit-Change-Number: 56103
Gerrit-PatchSet: 1
Gerrit-Owner: Alex Richardson <[email protected]>
Gerrit-MessageType: newchange
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