Re: [PATCH 5/5] target/ppc/kvm: Replace alloca() by g_malloc()

[Greg Kurz <groug@xxxxxxxx>]

On Wed,  5 May 2021 19:00:55 +0200
Philippe Mathieu-Daudé <philmd@xxxxxxxxxx> wrote:

> The ALLOCA(3) man-page mentions its "use is discouraged".
> 
> Replace it by a g_malloc() call.
> 
> Signed-off-by: Philippe Mathieu-Daudé <philmd@xxxxxxxxxx>
> ---
>  target/ppc/kvm.c | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/target/ppc/kvm.c b/target/ppc/kvm.c
> index 104a308abb5..ae62daddf7d 100644
> --- a/target/ppc/kvm.c
> +++ b/target/ppc/kvm.c
> @@ -2698,11 +2698,11 @@ int kvmppc_save_htab(QEMUFile *f, int fd, size_t bufsize, int64_t max_ns)
>  int kvmppc_load_htab_chunk(QEMUFile *f, int fd, uint32_t index,
>                             uint16_t n_valid, uint16_t n_invalid, Error **errp)
>  {
> -    struct kvm_get_htab_header *buf;
> -    size_t chunksize = sizeof(*buf) + n_valid * HASH_PTE_SIZE_64;
> +    size_t chunksize = sizeof(struct kvm_get_htab_header)

It is a bit unfortunate to introduce a new dependency on the struct type.

What about the following ?

-    struct kvm_get_htab_header *buf;
+    g_autofree struct kvm_get_htab_header *buf = NULL;
     size_t chunksize = sizeof(*buf) + n_valid * HASH_PTE_SIZE_64;
     ssize_t rc;
 
-    buf = alloca(chunksize);
+    buf = g_malloc(chunksize);


    g_autofree struct kvm_get_htab_header *buf = NULL;
    size_t chunksize = sizeof(*buf) + n_valid * HASH_PTE_SIZE_64;

> +                       + n_valid * HASH_PTE_SIZE_64;
>      ssize_t rc;
> +    g_autofree struct kvm_get_htab_header *buf = g_malloc(chunksize);
>  
> -    buf = alloca(chunksize);
>      buf->index = index;
>      buf->n_valid = n_valid;
>      buf->n_invalid = n_invalid;
> @@ -2741,10 +2741,10 @@ void kvmppc_read_hptes(ppc_hash_pte64_t *hptes, hwaddr ptex, int n)
>      i = 0;
>      while (i < n) {
>          struct kvm_get_htab_header *hdr;
> +        char buf[sizeof(*hdr) + HPTES_PER_GROUP * HASH_PTE_SIZE_64];
>          int m = n < HPTES_PER_GROUP ? n : HPTES_PER_GROUP;
> -        char buf[sizeof(*hdr) + m * HASH_PTE_SIZE_64];
>  
> -        rc = read(fd, buf, sizeof(buf));
> +        rc = read(fd, buf, sizeof(*hdr) + m * HASH_PTE_SIZE_64);
>          if (rc < 0) {
>              hw_error("kvmppc_read_hptes: Unable to read HPTEs");
>          }