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Re: [PATCH v5 5/7] xen/riscv: introduce trap_init()
- To: Julien Grall <julien@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 22 Mar 2023 15:02:28 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Gianluca Guida <gianluca@xxxxxxxxxxxx>, Bob Eshleman <bobbyeshleman@xxxxxxxxx>, Alistair Francis <alistair.francis@xxxxxxx>, Connor Davis <connojdavis@xxxxxxxxx>, Oleksii <oleksii.kurochko@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Wed, 22 Mar 2023 14:02:47 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 22.03.2023 14:51, Julien Grall wrote:
> I am a bit puzzled with what you wrote. From my understanding, with
> -noPIE, the compiler would be free to use absolute address rather than
> pc-relative one. Do you have any pointer to documentation that would
> back your reasoning?
It might for RV32 (using lui), but for 64-bit the ISA simply doesn't
have any halfway efficient means to load addresses in other than a
PC-relative manner [1]. -nopie really suppresses the compiler emitting
code going through .got (which then indeed would mean using absolute
addresses). I understand that at least for now RV32 isn't really of
interest; if it were, I guess the concern would be more significant.
Jan
[1] There aren't even suitable relocations to express such in ELF,
because you'd need to have a way to get at the top 32 bits of an
address. The only alternative would be .got-like indirection without
actually using .got.
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