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* [Bug sim/19447] mips sim fails some tests when using 64-bit address space
[not found] <bug-19447-4717@http.sourceware.org/bugzilla/>
@ 2021-04-16 11:38 ` fshahbazker at wavecomp dot com
2021-05-22 6:03 ` cvs-commit at gcc dot gnu.org
` (2 subsequent siblings)
3 siblings, 0 replies; 4+ messages in thread
From: fshahbazker at wavecomp dot com @ 2021-04-16 11:38 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=19447
Faraz Shahbazker <fshahbazker at wavecomp dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |fshahbazker at wavecomp dot com,
| |macro@linux-mips.org
--- Comment #1 from Faraz Shahbazker <fshahbazker at wavecomp dot com> ---
The sign-extension logic modeled by BFD is an integral part of the MIPS64
architecture spec. It appears in the virtual address map, where sign extension
allows for 32-bit compatibility segments [1] with 64-bit addressing. Truncating
these addresses prematurely in PC space breaks 64-bit builds
(-DWITH_TARGET_WORD_BITSIZE=64).
In the ISA itself, direct addressing (Load-Upper-Immediate) and indirect
addressing (Load-Word) both automatically sign-extend their results. These
instructions regenerate the sign-extended addresses even if we don't start with
one. That's what causes the failures in the report above.
Moreover, some instructions like ADD*/SUB* have unpredictable behaviour when an
operand is not correctly sign extended [3]. This affects PC-relative addressing
in particular. So arithmetic on the link-address generated in the return
address register by a jump-and-link is no longer possible, neither is the use
of the PC-relative addressing instructions provided by MIPSR6. I am preparing
upstream submission for R6, which is
where I first hit the problem.
As you might have seen, if we undo the PC address truncation, the earlier
common-read/write commit becomes problematic. Simple stuff like setting a
software breakpoint is no longer possible without some address translation for
MIPS. Even though I agree with the general premise that there is no MMU based
mapping, there is still a translation happening when addressing 32-bit memory
from 64-bit mode. This might be as trivial in h/w as leaving the upper address
lines unconnected, but it must be explicitly modeled in software by masking, if
not by a call to AddressTranslation, then elsewhere.
We might be able to work-around this by creating shadow memory in the
sign-extended space, but I think that is to over-wrought a solution. IN the
immeidiate term, I'd like to remove truncation of PC address and re-instate the
truncation on pAddr prior to calling to load_memory and store_memory
(sim/mips/sim-main.h). I am open to better suggestions.
[1] "MIPS64 Architecture for Programmers Volume III: The MIPS64
Privileged Resource Architecture", Document Number: MD00091,
Revision 6.02, December 10, 2015, Section 4.3 "Virtual Address
Spaces", pp. 29-31
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwjkk_jryv3vAhWDbysKHT4nDtIQFjACegQIAhAD&url=https%3A%2F%2Fs3-eu-west-1.amazonaws.com%2Fdownloads-mips%2Fdocuments%2FMD00091-2B-MIPS64PRA-AFP-06.03.pdf&usg=AOvVaw3bd2eW-vrsex-1URAFfeQT
[2] "MIPS64 Architecture for Programmers Volume II-A: The MIPS64
Instruction Set Reference Manual", Document Number: MD00087,
Revision 6.06, December 15, 2016, Section 3.2 "Alphabetical
List of Instructions", pp. 321
[3] "MIPS64 Architecture for Programmers Volume II-A: The MIPS64
Instruction Set Reference Manual", Document Number: MD00087,
Revision 6.06, December 15, 2016, Section 3.2 "Alphabetical
List of Instructions", pp. 56
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwje5dGMkf7vAhWEyDgGHU-jA8UQFjACegQIAxAD&url=https%3A%2F%2Fs3-eu-west-1.amazonaws.com%2Fdownloads-mips%2Fdocuments%2FMD00087-2B-MIPS64BIS-AFP-6.06.pdf&usg=AOvVaw2VR4VX1XSWo6efzaC6TxKH
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* [Bug sim/19447] mips sim fails some tests when using 64-bit address space
[not found] <bug-19447-4717@http.sourceware.org/bugzilla/>
2021-04-16 11:38 ` [Bug sim/19447] mips sim fails some tests when using 64-bit address space fshahbazker at wavecomp dot com
@ 2021-05-22 6:03 ` cvs-commit at gcc dot gnu.org
2021-10-03 15:39 ` vapier at gentoo dot org
2021-10-31 17:08 ` vapier at gentoo dot org
3 siblings, 0 replies; 4+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2021-05-22 6:03 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=19447
--- Comment #2 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Faraz Shahbazker <farazs@sourceware.org>:
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=b312488f1046a1b837561a4adf4323e29377cf12
commit b312488f1046a1b837561a4adf4323e29377cf12
Author: Faraz Shahbazker <fshahbazker@wavecomp.com>
Date: Wed May 5 04:51:16 2021 +0530
sim: mips: Only truncate sign extension bits for 32-bit target models
64-bit BFD for MIPS applies a standard sign extension on all addresses
assuming 64-bit target. These bits are required for 64-bit and can only
be safely truncated for 32-bit target models. This partially reverts commit
b36d953bced0a4fecdde1823abac70ed7038ee95
The sign-extension logic modeled by BFD is an integral part of the
MIPS64 architecture spec. It appears in the virtual address map, where
sign extension allows for 32-bit compatibility segments [1] with 64-bit
addressing. Truncating these addresses prematurely (commit
models (-DWITH_TARGET_WORD_BITSIZE=64).
In the ISA itself, direct addressing (Load-Upper-Immediate) and indirect
addressing (Load-Word) both automatically sign-extend their results. These
instructions regenerate the sign-extended addresses even if we don't start
with one (see pr gdb/19447).
Moreover, some instructions like ADD*/SUB* have unpredictable behaviour
when
an operand is not correctly sign extended [3]. This affects PC-relative
addressing in particular, so arithmetic on the link-address generated in
the
return address register by a jump-and-link is no longer possible, neither
is
the use of the PC-relative addressing instructions provided by MIPSR6.
[1] "MIPS64 Architecture for Programmers Volume III: The MIPS64
Privileged Resource Architecture", Document Number: MD00091,
Revision 6.02, December 10, 2015, Section 4.3 "Virtual Address
Spaces", pp. 29-31
https://s3-eu-west-1.amazonaws.com/downloads-mips/documents/MD00091-2B-MIPS64PRA-AFP-06.03.pdf
[2] "MIPS64 Architecture for Programmers Volume II-A: The MIPS64
Instruction Set Reference Manual", Document Number: MD00087,
Revision 6.06, December 15, 2016, Section 3.2 "Alphabetical
List of Instructions", pp. 321
https://s3-eu-west-1.amazonaws.com/downloads-mips/documents/MD00087-2B-MIPS64BIS-AFP-6.06.pdf
[3] "MIPS64 Architecture for Programmers Volume II-A: The MIPS64
Instruction Set Reference Manual", Document Number: MD00087,
Revision 6.06, December 15, 2016, Section 3.2 "Alphabetical
List of Instructions", pp. 56
https://s3-eu-west-1.amazonaws.com/downloads-mips/documents/MD00087-2B-MIPS64BIS-AFP-6.06.pdf
2021-04-23 Faraz Shahbazker <fshahbazker@wavecomp.com>
sim/mips/ChangeLog:
* interp.c (sim_create_inferior): Only truncate sign extension
bits for 32-bit target models
.
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* [Bug sim/19447] mips sim fails some tests when using 64-bit address space
[not found] <bug-19447-4717@http.sourceware.org/bugzilla/>
2021-04-16 11:38 ` [Bug sim/19447] mips sim fails some tests when using 64-bit address space fshahbazker at wavecomp dot com
2021-05-22 6:03 ` cvs-commit at gcc dot gnu.org
@ 2021-10-03 15:39 ` vapier at gentoo dot org
2021-10-31 17:08 ` vapier at gentoo dot org
3 siblings, 0 replies; 4+ messages in thread
From: vapier at gentoo dot org @ 2021-10-03 15:39 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=19447
--- Comment #3 from Mike Frysinger <vapier at gentoo dot org> ---
Faraz: is this bug fixed now with your changes ?
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* [Bug sim/19447] mips sim fails some tests when using 64-bit address space
[not found] <bug-19447-4717@http.sourceware.org/bugzilla/>
` (2 preceding siblings ...)
2021-10-03 15:39 ` vapier at gentoo dot org
@ 2021-10-31 17:08 ` vapier at gentoo dot org
3 siblings, 0 replies; 4+ messages in thread
From: vapier at gentoo dot org @ 2021-10-31 17:08 UTC (permalink / raw)
To: gdb-prs
https://sourceware.org/bugzilla/show_bug.cgi?id=19447
Mike Frysinger <vapier at gentoo dot org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |FIXED
Status|NEW |RESOLVED
--- Comment #4 from Mike Frysinger <vapier at gentoo dot org> ---
tests are passing, so assuming it's OK now
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[not found] <bug-19447-4717@http.sourceware.org/bugzilla/>
2021-04-16 11:38 ` [Bug sim/19447] mips sim fails some tests when using 64-bit address space fshahbazker at wavecomp dot com
2021-05-22 6:03 ` cvs-commit at gcc dot gnu.org
2021-10-03 15:39 ` vapier at gentoo dot org
2021-10-31 17:08 ` vapier at gentoo dot org
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