[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
bug#41357: 28.0.50; GC may miss to mark calle safe register content
From: |
Paul Eggert |
Subject: |
bug#41357: 28.0.50; GC may miss to mark calle safe register content |
Date: |
Sun, 17 May 2020 14:21:49 -0700 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 |
On 5/17/20 12:26 PM, Eli Zaretskii wrote:
> And where's GC in this picture? If it's called directly from 'f', can
> you show me such code in Emacs? Then we could disassembly it and see
> what we've got.
>
> Usually the code that calls GC is much deeper, and thus the chance of
> that temporary to stay in a register is very small, to say the least.
The probability is not that small, unfortunately. Compilers often have a habit
of running through the same set of callee-save registers in the same order.
Let's say you're on the x86 and your compiler consumes the four callee-save
registers in the order ebx, esi, edi, ebp. Then if we call f which calls g which
calls h which calls the GC, it's likely that f will save just ebx, then g will
save just ebx, esi, edi, then h will save just ebx and esi. Hence if the caller
has assigned a local variable to ebp, the GC won't see the variable's contents.
We should give Andrea a big round of applause for catching this bug.
- bug#41357: 28.0.50; GC may miss to mark calle safe register content, (continued)
- bug#41357: 28.0.50; GC may miss to mark calle safe register content, Andrea Corallo, 2020/05/17
- bug#41357: 28.0.50; GC may miss to mark calle safe register content, Eli Zaretskii, 2020/05/17
- bug#41357: 28.0.50; GC may miss to mark calle safe register content, Andrea Corallo, 2020/05/17
- bug#41357: 28.0.50; GC may miss to mark calle safe register content, Eli Zaretskii, 2020/05/17
- bug#41357: 28.0.50; GC may miss to mark calle safe register content, Andrea Corallo, 2020/05/17
- bug#41357: 28.0.50; GC may miss to mark calle safe register content, Paul Eggert, 2020/05/17
- bug#41357: 28.0.50; GC may miss to mark calle safe register content, Eli Zaretskii, 2020/05/17
- bug#41357: 28.0.50; GC may miss to mark calle safe register content, Paul Eggert, 2020/05/17
- bug#41357: 28.0.50; GC may miss to mark calle safe register content, Eli Zaretskii, 2020/05/17
- bug#41357: 28.0.50; GC may miss to mark calle safe register content, Andrea Corallo, 2020/05/17
- bug#41357: 28.0.50; GC may miss to mark calle safe register content,
Paul Eggert <=
bug#41357: 28.0.50; GC may miss to mark calle safe register content, Tom Tromey, 2020/05/24