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pan/bi: Fix M1/M2 decoding in disassembler

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C's definition of the % operator has a footgun around sign conversion.
Avoid it and just use bitwise arithemtic instead like the hardware
would, fixing the disassembly and making buggy assembly more obvious.

Fixes: 08a9e5e3e8 ("pan/bi: Decode M values in disasm")
Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8723>
(cherry picked from commit a69c73988b)
This commit is contained in:
Alyssa Rosenzweig 2021-01-08 21:38:09 -05:00 • committed by Dylan Baker
parent 26f5850810
commit 4169bef1b6
2 changed files with 10 additions and 8 deletions
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2
.pick_status.json
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@ -1093,7 +1093,7 @@
"description": "pan/bi: Fix M1/M2 decoding in disassembler",
"nominated": true,
"nomination_type": 1,
"resolution": 0,
"resolution": 1,
"master_sha": null,
"because_sha": "08a9e5e3e892e9acc7fcfc2cefb45990efa62e40"
},

16
src/panfrost/bifrost/disassemble.c
View file

@ -614,15 +614,17 @@ static bool dump_clause(FILE *fp, uint32_t *words, unsigned *size, unsigned offs
consts.raw[const_idx + 1] = const1;
/* Calculate M values from A, B and 4-bit
* unsigned arithmetic */
* unsigned arithmetic. Mathematically it
* should be (A - B) % 16 but we use this
* alternate form to avoid sign issues */
signed A1 = bits(words[2], 0, 4);
signed B1 = bits(words[3], 28, 32);
signed A2 = bits(words[1], 0, 4);
signed B2 = bits(words[2], 28, 32);
unsigned A1 = bits(words[2], 0, 4);
unsigned B1 = bits(words[3], 28, 32);
unsigned A2 = bits(words[1], 0, 4);
unsigned B2 = bits(words[2], 28, 32);
unsigned M1 = (A1 - B1) % 16;
unsigned M2 = (A2 - B2) % 16;
unsigned M1 = (16 + A1 - B1) & 0xF;
unsigned M2 = (16 + A2 - B2) & 0xF;
decode_M(&consts.mods[const_idx], M1, M2, false);