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Re: [PATCH] Linux: Use mmap instead of malloc in dirent/tst-getdents64
- From: Adhemerval Zanella <adhemerval dot zanella at linaro dot org>
- To: libc-alpha at sourceware dot org
- Date: Fri, 28 Jun 2019 08:22:41 -0300
- Subject: Re: [PATCH] Linux: Use mmap instead of malloc in dirent/tst-getdents64
- References: <87a7e2p01f.fsf@oldenburg2.str.redhat.com>
On 28/06/2019 05:49, Florian Weimer wrote:
> malloc dirties the entire allocated memory region due to M_PERTURB
> in the test harness.
>
> 2019-06-28 Florian Weimer <fweimer@redhat.com>
>
> * sysdeps/unix/sysv/linux/tst-getdents64.c (large_buffer_checks):
> Use mmap instead of malloc. malloc with M_PERTURB writes to the
> entire allocated memory range.
LGTM.
Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
>
> diff --git a/sysdeps/unix/sysv/linux/tst-getdents64.c b/sysdeps/unix/sysv/linux/tst-getdents64.c
> index 24e77e04d8..8a28e6c67c 100644
> --- a/sysdeps/unix/sysv/linux/tst-getdents64.c
> +++ b/sysdeps/unix/sysv/linux/tst-getdents64.c
> @@ -27,6 +27,7 @@
> #include <support/check.h>
> #include <support/support.h>
> #include <support/xunistd.h>
> +#include <sys/mman.h>
> #include <unistd.h>
>
> /* Called by large_buffer_checks below. */
> @@ -53,8 +54,13 @@ large_buffer_checks (int fd)
> size_t large_buffer_size;
> if (!__builtin_add_overflow (UINT_MAX, 2, &large_buffer_size))
> {
> - char *large_buffer = malloc (large_buffer_size);
> - if (large_buffer == NULL)
> + int flags = MAP_ANONYMOUS | MAP_PRIVATE;
> +#ifdef MAP_NORESERVE
> + flags |= MAP_NORESERVE;
> +#endif
> + void *large_buffer = mmap (NULL, large_buffer_size,
> + PROT_READ | PROT_WRITE, flags, -1, 0);
> + if (large_buffer == MAP_FAILED)
Should we really skip the test instead of using xmmap? The only case I think of
that it might fail is if kernel can't allocate bookeeping memory for the page
table itself, but I really think it unlikely (sanitizer usually allocates a
lot of VMA as well).
> printf ("warning: could not allocate %zu bytes of memory,"
> " subtests skipped\n", large_buffer_size);
> else
> @@ -65,8 +71,8 @@ large_buffer_checks (int fd)
> large_buffer_check (fd, large_buffer, UINT_MAX);
> large_buffer_check (fd, large_buffer, (size_t) UINT_MAX + 1);
> large_buffer_check (fd, large_buffer, (size_t) UINT_MAX + 2);
> + xmunmap (large_buffer, large_buffer_size);
> }
> - free (large_buffer);
> }
> }
>
>