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Date: Tue, 31 Dec 2019 20:25:00 -0800 From: Paul Burton <paulburton@...nel.org> To: "Jason A. Donenfeld" <Jason@...c4.com> Cc: Arnd Bergmann <arnd@...db.de>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "open list:BROADCOM NVRAM DRIVER" <linux-mips@...r.kernel.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 Hi Jason, On Tue, Dec 31, 2019 at 08:10:56PM -0800, Paul Burton wrote: > I'm still not quite sure *why* this happens; perhaps GCC just decides it > doesn't need to save & restore $gp/$28 when it spots that it's being > "used" for __current_thread_info (even though that's never actually > referenced in the VDSO)? Ah: > After defining a global register variable, for the current compilation > unit: > > - If the register is a call-saved register, call ABI is affected: the > register will not be restored in function epilogue sequences after > the variable has been assigned. Therefore, functions cannot safely > return to callers that assume standard ABI. https://gcc.gnu.org/onlinedocs/gcc/Global-Register-Variables.html That makes sense then. What doesn't make sense is how this ever worked. A question for another day... Thanks, Paul
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