From: Helge Deller <deller@gmx.de>
To: Richard Henderson <richard.henderson@linaro.org>,
Laurent Vivier <laurent@vivier.eu>,
qemu-devel@nongnu.org
Subject: [PATCH] target/hppa: Fix boot with old Linux installation CDs
Date: Sun, 30 Aug 2020 15:21:10 +0200 [thread overview]
Message-ID: <20200830132110.GA31329@ls3530.fritz.box> (raw)
The current qemu hppa emulation emulates a PA1.1 CPU, which can only
execute the 32-bit instruction set. For unknown 64-bit instructions, a
instruction trap is sent to the virtual CPU.
This behaviour is correct in the sense that we emulate what the PA1.1
specification says.
But when trying to boot older Linux installation images, e.g.
ftp://parisc.parisc-linux.org/debian-cd/debian-5.0/lenny-5.0.10-hppa-iso-cd/cdimage.debian.org/debian-5010-hppa-netinst.iso
one finds that qemu fails to boot those images.
This can be verified with:
qemu-system-hppa -cdrom debian-5010-hppa-netinst.iso -nographic
The problem is, that in the Linux kernel (e.g. 2.6.26) of those old
images 64-bit instructions were used by mistake in the fault handlers.
The relevant instructions (the ",*" indicates that it's a 64-bit
instruction) I see are:
0: 09 3e 04 29 sub,* sp,r9,r9
0: 08 3d 06 3d add,* ret1,r1,ret1
0: 0a 09 02 61 or,* r9,r16,r1
0: 0a ba 00 3a andcm,* r26,r21,r26
0: 08 33 02 33 and,* r19,r1,r19
The interesting part is, that real physical 32-bit machines (like the
700/64 and B160L - which is the one we emulate) do boot those images and
thus seem to simply ignore the 64-bit flag on those instructions.
The patch below modifies the qemu instruction decoder to ignore the
64-bit flag too - which is what real 32-bit hardware seems to do as
well. With this modification qemu now successfully boots those older
images too.
I suggest to apply the patch below - even if it does not reflect what
the SPEC says. Instead it increases the compatibility to really
existing hardware and seem to not create problems if we add real PA2.0
support anytime later.
Signed-off-by: Helge Deller <deller@gmx.de>
diff --git a/target/hppa/insns.decode b/target/hppa/insns.decode
index f0dd71dd08..dceaad65e9 100644
--- a/target/hppa/insns.decode
+++ b/target/hppa/insns.decode
@@ -149,9 +149,9 @@ lci 000001 ----- ----- -- 01001100 0 t:5
# Arith/Log
####
-andcm 000010 ..... ..... .... 000000 0 ..... @rrr_cf
-and 000010 ..... ..... .... 001000 0 ..... @rrr_cf
-or 000010 ..... ..... .... 001001 0 ..... @rrr_cf
+andcm 000010 ..... ..... .... 000000 - ..... @rrr_cf
+and 000010 ..... ..... .... 001000 - ..... @rrr_cf
+or 000010 ..... ..... .... 001001 - ..... @rrr_cf
xor 000010 ..... ..... .... 001010 0 ..... @rrr_cf
uxor 000010 ..... ..... .... 001110 0 ..... @rrr_cf
ds 000010 ..... ..... .... 010001 0 ..... @rrr_cf
@@ -161,13 +161,13 @@ uaddcm_tc 000010 ..... ..... .... 100111 0 ..... @rrr_cf
dcor 000010 ..... 00000 .... 101110 0 ..... @rr_cf
dcor_i 000010 ..... 00000 .... 101111 0 ..... @rr_cf
-add 000010 ..... ..... .... 0110.. 0 ..... @rrr_cf_sh
+add 000010 ..... ..... .... 0110.. - ..... @rrr_cf_sh
add_l 000010 ..... ..... .... 1010.. 0 ..... @rrr_cf_sh
add_tsv 000010 ..... ..... .... 1110.. 0 ..... @rrr_cf_sh
add_c 000010 ..... ..... .... 011100 0 ..... @rrr_cf_sh0
add_c_tsv 000010 ..... ..... .... 111100 0 ..... @rrr_cf_sh0
-sub 000010 ..... ..... .... 010000 0 ..... @rrr_cf
+sub 000010 ..... ..... .... 010000 - ..... @rrr_cf
sub_tsv 000010 ..... ..... .... 110000 0 ..... @rrr_cf
sub_tc 000010 ..... ..... .... 010011 0 ..... @rrr_cf
sub_tsv_tc 000010 ..... ..... .... 110011 0 ..... @rrr_cf
next reply other threads:[~2020-08-30 13:25 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-30 13:21 Helge Deller [this message]
2020-08-30 15:05 ` [PATCH] target/hppa: Fix boot with old Linux installation CDs Richard Henderson
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