From: JIANG Muhui <1925512@bugs.launchpad.net>
To: qemu-devel@nongnu.org
Subject: [Bug 1925512] Re: UNDEFINED case for instruction BLX
Date: Thu, 22 Apr 2021 19:29:59 -0000 [thread overview]
Message-ID: <161911980004.9771.6887610667740746888.malone@wampee.canonical.com> (raw)
In-Reply-To: 161909962601.31655.7052824363126074861.malonedeb@soybean.canonical.com
Hi
I still feel QEMU's implementation is not right. Could you please check
it again.
According to https://developer.arm.com/documentation/ddi0406/c
/Application-Level-Architecture/Instruction-Details/Alphabetical-list-
of-instructions/BL--BLX--immediate-?lang=en
The encoding T2 for BLX is below:
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
1 1 1 1 0 S | imm10H | 1 1 J1 0 J2 | imm10L |H
In the ASL of ARM, we have H == '1' then UNDEFINED;
Symbol *H* represents the last bit of this instruction. I am not sure
whether a->imm includes the symbol *H*. I double checked the file
`t32.decode` and it seems so (It would be great if you can tell me what
a->imm indeed represents in BLX).
However, UNDEFINED means unallocated encoding in ARM manual. The right
behavior might be something like below:
if (s->thumb && (a->imm & 2)) {
unallocated_encoding(s);
return true;
}
Correct me if I am wrong. I can also provide test case if you need. Many
Thanks
Regards
Muhui
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https://bugs.launchpad.net/bugs/1925512
Title:
UNDEFINED case for instruction BLX
Status in QEMU:
Invalid
Bug description:
Hi
I refer to the instruction BLX imm (T2 encoding) in ARMv7 (Thumb
mode).
11110 S imm10H 11 J1 0 J2 imm10L H
if H == '1' then UNDEFINED;
I1 = NOT(J1 EOR S); I2 = NOT(J2 EOR S); imm32 = SignExtend(S:I1:I2:imm10H:imm10L:'00', 32);
targetInstrSet = InstrSet_A32;
if InITBlock() && !LastInITBlock() then UNPREDICTABLE;
According to the manual, if H equals to 1, this instruction should be
an UNDEFINED instruction. However, it seems QEMU does not check this
constraint in function trans_BLX_i. Thanks
Regards
Muhui
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next prev parent reply other threads:[~2021-04-22 19:36 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-22 13:53 [Bug 1925512] [NEW] UNDEFINED case for instruction BLX JIANG Muhui
2021-04-22 15:00 ` [Bug 1925512] " Philippe Mathieu-Daudé
2021-04-22 16:06 ` Richard Henderson
2021-04-22 19:29 ` JIANG Muhui [this message]
2021-04-22 21:38 ` Richard Henderson
2021-04-23 6:52 ` JIANG Muhui
2021-04-23 15:20 ` Richard Henderson
2021-04-23 17:14 ` Richard Henderson
2021-05-26 15:38 ` Thomas Huth
2021-08-25 7:11 ` Thomas Huth
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