Re: [PATCH 17/22] Implement do_obreak function

[Warner Losh <imp@bsdimp.com>]

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On Sat, Aug 19, 2023 at 3:49 AM Karim Taha <kariem.taha2.7@gmail.com> wrote:

> From: Stacey Son <sson@FreeBSD.org>
>
> Co-authored-by: Mikaël Urankar <mikael.urankar@gmail.com>
>
> Signed-off-by: Mikaël Urankar <mikael.urankar@gmail.com>
> Signed-off-by: Stacey Son <sson@FreeBSD.org>
> Signed-off-by: Karim Taha <kariem.taha2.7@gmail.com>
> ---
>  bsd-user/bsd-mem.h            | 85 +++++++++++++++++++++++++++++++++++
>  bsd-user/freebsd/os-syscall.c |  7 +++
>  2 files changed, 92 insertions(+)
>

emacs works with this, iirc, and it's super picky about brk being
pedantically correct.
This also doesn't match current linux-user. Perhaps the caution it uses is
no longer
needed? I think it's another area we should invite the linux-user
maintainers to
comment.

Warner



> diff --git a/bsd-user/bsd-mem.h b/bsd-user/bsd-mem.h
> index edbccd3111..6f33148eb7 100644
> --- a/bsd-user/bsd-mem.h
> +++ b/bsd-user/bsd-mem.h
> @@ -167,4 +167,89 @@ static inline abi_long do_bsd_mincore(abi_ulong
> target_addr, abi_ulong len,
>      return ret;
>  }
>
> +#ifdef DO_DEBUG
> +#define DEBUGF_BRK(message, args...) \
> +    do { fprintf(stderr, (message), ## args); } while (0)
> +#else
> +#define DEBUGF_BRK(message, args...)
> +#endif
> +
> +/* do_brk() must return target values and target errnos. */
> +static inline abi_long do_obreak(abi_ulong new_brk)
> +{
> +    abi_long mapped_addr;
> +    int new_alloc_size;
> +
> +    DEBUGF_BRK("do_brk(" TARGET_ABI_FMT_lx ") -> ", new_brk);
> +
> +    if (!new_brk) {
> +        DEBUGF_BRK(TARGET_ABI_FMT_lx " (!new_brk)\n", bsd_target_brk);
> +        return bsd_target_brk;
> +    }
> +    if (new_brk < bsd_target_original_brk) {
> +        DEBUGF_BRK(TARGET_ABI_FMT_lx " (new_brk <
> bsd_target_original_brk)\n",
> +                   bsd_target_brk);
> +        return bsd_target_brk;
> +    }
> +
> +    /*
> +     * If the new brk is less than the highest page reserved to the
> target heap
> +     * allocation, set it and we're almost done...
> +     */
> +    if (new_brk <= brk_page) {
> +        /*
> +         * Heap contents are initialized to zero, as for anonymous mapped
> pages.
> +         */
> +        if (new_brk > bsd_target_brk) {
> +            memset(g2h_untagged(bsd_target_brk), 0, new_brk -
> bsd_target_brk);
> +        }
> +        bsd_target_brk = new_brk;
> +        DEBUGF_BRK(TARGET_ABI_FMT_lx " (new_brk <= brk_page)\n",
> +                   bsd_target_brk);
> +        return bsd_target_brk;
> +    }
> +
> +    /*
> +     * We need to allocate more memory after the brk... Note that we
> don't use
> +     * MAP_FIXED because that will map over the top of any existing
> mapping
> +     * (like the one with the host libc or qemu itself); instead we treat
> +     * "mapped but at wrong address" as a failure and unmap again.
> +     */
> +    new_alloc_size = HOST_PAGE_ALIGN(new_brk - brk_page);
> +    mapped_addr = get_errno(target_mmap(brk_page, new_alloc_size,
> +                                        PROT_READ | PROT_WRITE,
> +                                        MAP_ANON | MAP_PRIVATE, -1, 0));
> +
> +    if (mapped_addr == brk_page) {
> +        /*
> +         * Heap contents are initialized to zero, as for anonymous mapped
> pages.
> +         * Technically the new pages are already initialized to zero
> since they
> +         * *are* anonymous mapped pages, however we have to take care
> with the
> +         * contents that come from the remaining part of the previous
> page: it
> +         * may contains garbage data due to a previous heap usage (grown
> then
> +         * shrunken).
> +         */
> +        memset(g2h_untagged(bsd_target_brk), 0, brk_page -
> bsd_target_brk);
> +
> +        bsd_target_brk = new_brk;
> +        brk_page = HOST_PAGE_ALIGN(bsd_target_brk);
> +        DEBUGF_BRK(TARGET_ABI_FMT_lx " (mapped_addr == brk_page)\n",
> +            bsd_target_brk);
> +        return bsd_target_brk;
> +    } else if (mapped_addr != -1) {
> +        /*
> +         * Mapped but at wrong address, meaning there wasn't actually
> enough
> +         * space for this brk.
> +         */
> +        target_munmap(mapped_addr, new_alloc_size);
> +        mapped_addr = -1;
> +        DEBUGF_BRK(TARGET_ABI_FMT_lx " (mapped_addr != -1)\n",
> bsd_target_brk);
> +    } else {
> +        DEBUGF_BRK(TARGET_ABI_FMT_lx " (otherwise)\n", bsd_target_brk);
> +    }
> +
> +    /* For everything else, return the previous break. */
> +    return bsd_target_brk;
> +}
> +
>  #endif /* BSD_USER_BSD_MEM_H */
> diff --git a/bsd-user/freebsd/os-syscall.c b/bsd-user/freebsd/os-syscall.c
> index 1db0907504..1b9dca9164 100644
> --- a/bsd-user/freebsd/os-syscall.c
> +++ b/bsd-user/freebsd/os-syscall.c
> @@ -543,6 +543,13 @@ static abi_long freebsd_syscall(void *cpu_env, int
> num, abi_long arg1,
>          break;
>  #endif
>
> +        /*
> +         * Misc
> +         */
> +    case TARGET_FREEBSD_NR_break:
> +        ret = do_obreak(arg1);
> +        break;
> +
>          /*
>           * sys{ctl, arch, call}
>           */
> --
> 2.40.0
>
>

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