linux-kernel - Re: [PATCH] mips: vdso: conditionalize 32-bit time functions on COMPAT_32BIT

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Date:   Mon, 30 Dec 2019 16:58:17 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@...r.kernel.org>,
        Paul Burton <paulburton@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Christian Brauner <christian.brauner@...onical.com>
Subject: Re: [PATCH] mips: vdso: conditionalize 32-bit time functions on COMPAT_32BIT_TIME

Makes sense w.r.t. time32 situation.

I still think that in spite of that there's still something weird
happening with the mips VDSO.

Here's a register dump before the call:

 $ 0   : 0000000000000000 0000000000000001 0000000010000000 fffffffffffffffc
 $ 4   : 0000000000000002 000000007fff2e40 0000000000000000 0000000000000001
 $ 8   : 0000000000000000 0000000000000000 0000000000000000 0000000000000000
 $12   : 0000000000000000 000000000000000a ffffffff80000000 000000007fffffda
 $16   : 0000000010001ba8 0000005800000015 0000000010000000 0000000010000000
 $20   : 0000000010000000 0000000010000000 0000000000000000 0000000077ff2ae8
 $24   : 0000000000000005 0000000077fa1d18
 $28   : 0000000010019cf0 000000007fff2e40 0000000000000000 0000000010000c30
 Hi    : 0000000000000000
 Lo    : 0000000000000000
 epc   : 0000000077fa1d18 0x77fa1d18
 ra    : 0000000010000c30 0x10000c30

And here it is immediately after:

 $ 0   : 0000000000000000 0000000000000001 ffffffffffffffa7 000000007fff5000
 $ 4   : 0000000000000002 000000007fff2e40 0000000077ff2000 0000000000000001
 $ 8   : 0000000000000006 0000000000000020 0000000000000002 0000000000000000
 $12   : 0000000000000000 0000000000001852 ffffffff80156160 000000007fffffda
 $16   : 0000000010001ba8 0000005800000015 0000000010000000 0000000010000000
 $20   : 0000000010000000 0000000010000000 0000000000000000 0000000077ff2b00
 $24   : 0000000000000005 0000000000000000
 $28   : 000000007fff5000 000000007fff2e30 0000000000000000 0000000077fa1e00
 Hi    : 0000000000000000
 Lo    : 0000000000000000
 epc   : 0000000077fa1e00 0x77fa1e00
 ra    : 0000000077fa1e00 0x77fa1e00

I wonder if a toolchain option or compiler bug or something is causing
the vdso to not restore certain registers (gp? ra?).