Re: [PATCH v2 4/5] linux-user: Add x86_64 vsyscall page to /proc/self/maps

["Alex Bennée" <alex.bennee@linaro.org>]

Richard Henderson <richard.henderson@linaro.org> writes:

> The page isn't (necessarily) present in the host /proc/self/maps,
> and even if it might be it isn't present in page_flags, and even
> if it was it might not have the same set of page permissions.
>
> The easiest thing to do, particularly when it comes to the
> "[vsyscall]" note at the end of line, is to special case it.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  linux-user/syscall.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/linux-user/syscall.c b/linux-user/syscall.c
> index 171c0caef3..eb867a5296 100644
> --- a/linux-user/syscall.c
> +++ b/linux-user/syscall.c
> @@ -7005,6 +7005,15 @@ static int open_self_maps(void *cpu_env, int fd)
>          }
>      }
>  
> +#ifdef TARGET_X86_64
> +    /*
> +     * We only support execution from the vsyscall page.
> +     * This is as if CONFIG_LEGACY_VSYSCALL_XONLY=y from v5.3.
> +     */
> +    dprintf(fd, "ffffffffff600000-ffffffffff601000 --xp 00000000 00:00 0"
> +                "          [vsyscall]\n");
> +#endif
> +

I'm not sure what whitespace is wrong - tabs maybe? But looking at a
real vsyscall system vs emulated things line up better:

  Welcome to Buildroot
  buildroot login: root
  # uname -a
  Linux buildroot 5.4.13 #1 SMP Mon Jan 20 14:36:20 GMT 2020 x86_64 GNU/Linux
  # cat /proc/self/maps
  00400000-004ab000 r-xp 00000000 00:02 7635                               /bin/busybox
  004ab000-004ac000 r-xp 000aa000 00:02 7635                               /bin/busybox
  004ac000-004ad000 rwxp 000ab000 00:02 7635                               /bin/busybox
  004ad000-004ae000 rwxp 00000000 00:00 0
  7fcc91566000-7fcc91567000 rwxp 00000000 00:00 0
  7fcc91567000-7fcc915de000 r-xp 00000000 00:02 7475                       /lib/libuClibc-1.0.32.so
  7fcc915de000-7fcc915df000 ---p 00000000 00:00 0
  7fcc915df000-7fcc915e0000 r-xp 00077000 00:02 7475                       /lib/libuClibc-1.0.32.so
  7fcc915e0000-7fcc915e1000 rwxp 00078000 00:02 7475                       /lib/libuClibc-1.0.32.so
  7fcc915e1000-7fcc915fc000 rwxp 00000000 00:00 0
  7fcc915fc000-7fcc91603000 r-xp 00000000 00:02 7480                       /lib/ld64-uClibc-1.0.32.so
  7fcc91603000-7fcc91604000 r-xp 00006000 00:02 7480                       /lib/ld64-uClibc-1.0.32.so
  7fcc91604000-7fcc91605000 rwxp 00007000 00:02 7480                       /lib/ld64-uClibc-1.0.32.so
  7ffd92001000-7ffd92022000 rwxp 00000000 00:00 0                          [stack]
  7ffd920c3000-7ffd920c6000 r--p 00000000 00:00 0                          [vvar]
  7ffd920c6000-7ffd920c7000 r-xp 00000000 00:00 0                          [vdso]
  ffffffffff600000-ffffffffff601000 r-xp 00000000 00:00 0                  [vsyscall]
  # QEMU 4.2.50 monitor - type 'help' for more information
  (qemu) quit
  14:38:52 [alex.bennee@hackbox2:~/l/q/b/all] review/fix-user-brk|… + ./x86_64-linux-user/qemu-x86_64 /bin/cat /proc/self/maps
  4000000000-4000008000 r-xp 00000000 00:19 8131          /bin/cat
  4000008000-4000207000 ---p 00000000 00:00 0
  4000207000-4000208000 r--p 00007000 00:19 8131          /bin/cat
  4000208000-4000209000 rw-p 00008000 00:19 8131          /bin/cat
  4000209000-400022a000 rw-p 00000000 00:00 0
  4001209000-400120a000 ---p 00000000 00:00 0
  400120a000-4001a0a000 rw-p 00000000 00:00 0                [stack]
  4001a0a000-4001a31000 r-xp 00000000 00:19 3644          /lib/x86_64-linux-gnu/ld-2.27.so
  4001a31000-4001c31000 ---p 00000000 00:00 0
  4001c31000-4001c32000 r--p 00027000 00:19 3644          /lib/x86_64-linux-gnu/ld-2.27.so
  4001c32000-4001c33000 rw-p 00028000 00:19 3644          /lib/x86_64-linux-gnu/ld-2.27.so
  4001c33000-4001c36000 rw-p 00000000 00:00 0
  4001c6d000-4001e54000 r-xp 00000000 00:19 3648          /lib/x86_64-linux-gnu/libc-2.27.so
  4001e54000-4002054000 ---p 001e7000 00:19 3648          /lib/x86_64-linux-gnu/libc-2.27.so
  4002054000-4002058000 r--p 001e7000 00:19 3648          /lib/x86_64-linux-gnu/libc-2.27.so
  4002058000-400205a000 rw-p 001eb000 00:19 3648          /lib/x86_64-linux-gnu/libc-2.27.so
  400205a000-4002060000 rw-p 00000000 00:00 0
  4002060000-40023d2000 r--p 00000000 00:19 195276          /usr/lib/locale/locale-archive
  ffffffffff600000-ffffffffff601000 --xp 00000000 00:00 0          [vsyscall]

>      free(line);
>      fclose(fp);


-- 
Alex Bennée