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target/arm/arm-semi: fix SYS_OPEN to return nonzero filehandle 

According to the specification "Semihosting for AArch32 and Aarch64",
the SYS_OPEN operation should return:

 - A nonzero handle if the call is successful
 - -1 if the call is not successful

So, it should never return 0.

Prior to commit 35e9a0a8ce ("target/arm/arm-semi: Make semihosting
code hand out its own file descriptors"), the guest fd matched to the
host fd. It returned a nonzero handle on success since the fd 0 is
already used for stdin.

Now that the guest fd is the index of guestfd_array, it starts from 0.

I noticed this issue particularly because Trusted Firmware-A built with
PLAT=qemu is no longer working. Its io_semihosting driver only handles
a positive return value as a valid filehandle.

Basically, there are two ways to fix this:

  - Use (guestfd - 1) as the index of guestfs_arrary. We need to insert
    increment/decrement to convert the guestfd and the array index back
    and forth.

  - Keep using guestfd as the index of guestfs_array. The first entry
    of guestfs_array is left unused.

I thought the latter is simpler. We end up with wasting a small piece
of memory for the unused first entry of guestfd_array, but this is
probably not a big deal.

Fixes: 35e9a0a8ce ("target/arm/arm-semi: Make semihosting code hand out its own file descriptors")
Cc: qemu-stable@nongnu.org
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20200109041228.10131-1-masahiroy@kernel.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Masahiro Yamada 2020-01-17 14:09:30 +00:00 committed by Peter Maydell
parent af4ba4ed13
commit 21bf9b06cb
1 changed files with 3 additions and 2 deletions
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5
target/arm/arm-semi.c
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@ -144,7 +144,8 @@ static int alloc_guestfd(void)
guestfd_array = g_array_new(FALSE, TRUE, sizeof(GuestFD));
}
for (i = 0; i < guestfd_array->len; i++) {
/* SYS_OPEN should return nonzero handle on success. Start guestfd from 1 */
for (i = 1; i < guestfd_array->len; i++) {
GuestFD *gf = &g_array_index(guestfd_array, GuestFD, i);
if (gf->type == GuestFDUnused) {
@ -168,7 +169,7 @@ static GuestFD *do_get_guestfd(int guestfd)
return NULL;
}
if (guestfd < 0 || guestfd >= guestfd_array->len) {
if (guestfd <= 0 || guestfd >= guestfd_array->len) {
return NULL;
}